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3 LIBRARY
”099 Michigan State
University

This is to certify that the
dissertation entitled

The Effect of MCP on the Quality of F resh-cut Apples and the
Development of MCP Controlled Release Devices

presented by

Krittika Tanprasert

has been accepted towards fulfillment
of the requirements for the

Ph. D. degree in Packaging

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THE EFFECT OF MCP ON THE QUALITY OF FRESH-CUT APPLES AND THE
DEVELOPMENT OF MCP CONTROLLED RELEASE DEVICES

By

Krittika Tanprasert

A DISSERTATION
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
DOCTOR OF PHILOSOPHY
School of Packaging

2005

ABSTRACT

THE EFFECT OF MCP ON THE QUALITY OF FRESH-CUT APPLES AND THE
DEVELOPMENT OF MCP CONTROLLED RELEASE DEVICES

By

Krittika Tanprasert

1-Methylcyclopropene (MCP), an ethylene antagonist, can be used to
extend the storage life and shelf life of horticultural crops. The cultural use of
MCP on fruits and vegetables is a single application after harvest. This
dissertation relates to two aspects of MCP: first, the potential of MCP-treated
apples as a raw material for fresh-cut apples and, second, development of a
controlled release device to enable continuous in-package application of MCP.

Fresh-cut apples are increasingly more popular and have the potential to
increase the revenue stream of the apple industry. One of the objectives of this
study is to evaluate how postharvest treatments such as MCP and controlled
atmosphere (CA) storage, individually and in combination, affect the subsequent
quality of fresh-cut apples over 9 month storage period. The combination of
MCP treatment and CA storage resulted in slices with superior firmness but were
highly susceptible to enzymatic browning. The combination treatment resulted in
apple slices having a different volatile profile from apples receiving either of the
individual treatments. MCP + CA storage apples are suitable as a raw material
for fresh-cut apples only when the enzymatic browning can be minimized. When
this is not the case, MCP treated apples and CA storage apples are the better

choice to use. At 3 and 9 months storage of intact apples, MCP-treated apples

were better than CA-storage apples. At 3 months, MCP treated apples had
greater firmness and less susceptibility to enzymatic browning. At 9 months, the
firmness of MCP treated apples was greater than the minimum threshold level
and the slices were less sensitive to enzymatic browning than CA storage
apples. At 5 and 7 month storage, CA storage apples and MCP treated apples
resulted in slices with a similar quality.

The other objective of this study was to develop controlled release devices
to enable a continuous in-package MCP treatment. Then, the release
characteristics of several developed devices were evaluated as a function of
temperature and relative humidity. In this study, four controlled release devices,
monolithic (LDPE and EVA matrices) and reservoir (LDPE and EVA membrane)
were developed. None of the devices released 100% of the available MCP.
Among them, the LDPE monolithic device had the most desirable characteristics.
The release characteristics of the device depended greatly on temperature and
relative humidity. The total amount of MCP released and the release rate
increased with increasing temperature. The effect of relative humidity at 22 and
5°C were different. The amount of MCP released and the release rate increased
with an increasing RH at 22°C but RH had little effect at 5°C. It is anticipated that
the device will to be used as a supplement to the single application after harvest
for produce such as tomatoes, apples, and avocados that benefit from repeated

or continuous treatment MCP treatment.

Copyright by
KRlTl'lKA TANPRASERT
2005

This dissertation is dedicated to

My late grandpa, Mr. Preecha Tanprasert,
My late grandma, Mrs. Sirilak Anomasiri
and

the late Dr. Ruben Hernandez

ACKNOWLEDGEMENTS

I am indebted to many people for their help and support throughout my
graduate study. Since this acknowledgement section is too short to adequately
express my appreciation to everyone, I hope those not mentioned here know
their contribution is no less appreciated and that they forgive me.

First of all I would like to thank my advisors and committees. Beginning in
chronological order, Dr. Ruben Hernandez, who was my advisor for my master
degree and the early part of my PhD, provided guidance and presented an
opportunity for me to pursue the PhD. Due to Dr. Hernandez’s untimely death,
Dr. Bruce Harte became my new advisor. I greatly appreciate his decision to
accept me even with his busy schedule. Dr. Randy Beaudry has been pivotal to
this research. He not only provided apples, MCP, and his lab facility but also
taught me several lab techniques and gave advice on planning the experiment.
l’m greatly indebted to both Dr. Harte and Dr. Beaudry, the two most wonderful
persons, for their continuous guidance, support, generosity and encouragement.
I am also thankful to my committee, Dr. Susan Selke and Dr. Theron Downes, for
their invaluable advice and suggestions.

I also want to thank the faculty and staff at the School of Packaging. A
special thank you goes to Dr. Hugh Lockhart who sparked my interest in medical
packaging and gave me an opportunity to be more involved in this area. Also, to

Dr. Robert Clarke who got me involved in RFlD research. They both have been

vi

great mentors in and out of their research areas. I am also grateful to Linda
Estill, Colleen Wager, and Mary Anne Merrill for their great help.

I would like express my deep gratitude to Mr. Phillip Lynch, Chairman of
Northern Technology International Corp, for his generous offer for part-time work
with NTlC and the financial support during the last year of my PhD.

Special thanks to all my friends. Thanks to friends from MSU for their
friendship and assistance. Those who deserve special mention are Dr.
Hernandez’s research group (Cengiz, Antonis, Pillar, Kata, Younsuk, Sukasem,
Dario, Rafael), Hsin—Yen Chung, Bob Hunivitz, Pankaj Kumar, Jaemin Choi,
Norbismi Nordin, lsinay Yuzay, Xiong Li, and the Thai Packaging students. My
appreciation also extends to friends from Triamudom and KMITL for their long
lasting friendship even when I have been away for a long time.

I am deeply indebted to David Lockhart for being there for me through
good times and bad, Dr. & Mrs. Lockhart, Kathi Lockhart and Caryn & Allan
Coyle, for being like my family. They have made being far away from home life
easier and enjoyable.

I am greatly thankful for my parents, Gen. Dr. Pravit and Dr. Kunnikar
Tanprasert, who teach me the value of education and give me invaluable advice.
Without their unconditional love and support, I could never have completed this
work. My appreciation extends to Mr. Sawang Lertthirasuntorn for his enduring
love and for patiently waiting for me. His unfailing support and encouragement in

the last couple months are a significant part of the completion of this dissertation.

vii

TABLE OF CONTENTS

LIST OF TABLES ................................................................................................. xi
LIST OF FIGURES .............................................................................................. xv
Introduction .......................................................................................................... 1
1 Literature Review .......................................................................................... 3
1.1 Introduction ............................................................................................ 3
1. 2 1- -Methylcyclopropene ............................................................................ 6
1. 3 The effect of MCP on fresh fruits and vegetables ................................ 10
1.3.1 Apple (Ma/us Pumila) .................................................................... 10

1. 3. 2 Apricot (Prunus armeniaca) ......................................................... 15

1. 3. 3 Avocado (Persea amen'cana) ....................................................... 16

1 3. 4 Banana (Musa paradisiacal) ......................................................... 17

1. 3. 5 Broccoli (Brassica oleracea) ......................................................... 19

1. 3. 6 Cherry (Prunus avium) .................................................................. 20

1. 3. 7 Coriander (Con'andrum sativum) ................................................... 21

1. 3. 8 Custard apple (Annona chen'mola) ............................................... 21

1. 3. 9 Mango (Mangifera indica) ............................................................. 22
1.3.10 Nectarine (anus persica) ........................................................... 24

1 ..3 11 Orange (Citrus sinensis) ............................................................... 25
1.3.12 Papaya (Can'ca papaya) ............................................................... 25
1.3.13 Pear (Pyrus communis) ................................................................ 25

1. 3.14 Persimmon (Dispyros kakr) ........................................................... 26
1.3.15 Pineapple (Ananas comosus) ....................................................... 26
1.3.16 Plum (Prunus domestica) ............................................................. 27
1.3.17 Rambutan (Nephelium Iappaceum) .............................................. 29
1.3.18 Strawberry (Fragaria spp.) ............................................................ 29
1.3.19 Tomato (L ycopersicon esculentum) .............................................. 30

1.4 The effect of MCP on fresh-cut produce .............................................. 31

1 ..4 1 Fresh-cut apples ........................................................................... 31

1 4. 2 Fresh-cut lettuce ........................................................................... 33

1 ..4 3 Fresh-cut pineapples .................................................................... 33

1 .4 4 Fresh-cut tomato ........................................................................... 34

1 .4 5 Fresh-cut watermelon ................................................................... 34

1. 5 MCP commercialization ....................................................................... 35

1 .6 MCP delivery system ........................................................................... 35
1.7 Conclusion ........................................................................................... 42

2 The Effect of Postharvest Conditions on Subsequent Quality of Fresh-cut
Apples ................................................................................................................ 43
2.1 Introduction .......................................................................................... 43

viii

2.2 Materials and Methods ......................................................................... 47

2.2.1 Plant materials .............................................................................. 47
2.2.2 MCP treatment and storage conditions ......................................... 47
2.2.3 Internal ethylene content .............................................................. 48
2.2.4 Total soluble solids ....................................................................... 48
2.2.5 Firmness ....................................................................................... 48
2.2.6 Flesh color measurement ............................................................. 49
2.2.7 Fresh-cut apple preparation .......................................................... 49
2.2.8 The effect of postharvest condition on flesh color of fresh-cut
apples ........................................................................................... 49
2.2.9 The effect of postharvest condition on texture of fresh-cut apples 50
2.2.10 The effect of postharvest condition on volatile production by apple
slices ............................................................................................. 51
2.2.1 1 Statistical analysis ........................................................................ 52
2.3 Results and Discussion ........................................................................ 53
2.3.1 Condition of apples before fresh-cut apple processing ................. 53
2.3.2 The effect of postharvest condition on flesh color of fresh-cut
apples ........................................................................................... 64
2.3.3 The effect of postharvest condition on texture of fresh-cut apples 83
2.3.4 The effect of postharvest condition on volatiles of fresh-cut apples..
...................................................................................................... 88
2.4 Summary and Conclusion .................................................................. 105

3 Development of 1-Methylcyclopropene Controlled Release Delivery Device.

.................................................................................................................. 107
3.1 Introduction ........................................................................................ 107
3.2 Materials and Methods ....................................................................... 111

3.2.1 Polymer matrices ........................................................................ 1 1 1

3.2.2 Active compound ........................................................................ 111

3.2.3 Thermal analysis ......................................................................... 11 1

3.2.4 MCP analysis .............................................................................. 112

3.2.5 Barrier properties ........................................................................ 112

3.2.6 MCP controlled release devices ................................................. 116

3.2.7 Release of MCP .......................................................................... 118

3.2.8 The effect of MCP delivery devices on the MCP release

characteristics ............................................................................. 120

3.2.9 The effect of temperature on the release of MCP ....................... 121

3.2.10 The effect of relative humidity on the release of MCP ................ 122
3.3 Results and Discussion ...................................................................... 122

3.3.1 Thermal analysis ......................................................................... 122

3.3.2 Barrier properties ........................................................................ 126

3.3.3 The effect of MCP delivery devices on the MCP release

characteristics ............................................................................. 130

3.3.4 The effect of temperature on the release of MCP ....................... 142

3.3.5 The effect of relative humidity on the release of MCP at 22°C 147

ix

3.3.6 The effect of relative humidity on the release of MCP at 5°C ..... 157

3.4 Summary and Conclusion .................................................................. 164
Conclusion ....................................................................................................... 166
APPENDICES .................................................................................................. 168

APPENDIX A SAS Codes for Statistical Analysis of Apples Condition and
Fresh-cut apples Quality ........................................................................ 169
Appendix B Statistical Analysis of ohe Effect of Postharvest Treatments
on the Subsequent Quality of F res-cut Apples ...................................... 171
B1. The Effect of Postharvest Treatment on The Condition of Intact
Apples Before Processing ........................................................... 171
B2. The Effect of Postharvest Treatment on the Flesh Color of
Fresh-cut Apples ......................................................................... 175
B3. The Effect of Postharvest Treatment on the Texture of F resh-
cut Apples ................................................................................... 181
B4. The Effect of Postharvest Treatment on the Hexyl Acetate
Concentration of FC Apples ........................................................ 183
APPENDIX C MCP Calibration Curve .................................................. 185
APPENDIX D Calculation of the Required Amount of SmartfreshTM ..... 187
Bibliography ..................................................................................................... 189

LIST OF TABLES

Table 1.1 Summary of listing MCP concentration and treatment duration and
temperature that provide beneficial effect to fruits and vegetables (modified from
Blankenship and Dole, 2003) ............................................................................... 8

Table 2.1. Pearson correlation coefficients and p-values of correlation evaluation
between flesh firmness (N) and log IEC for untreated ‘Jonagold’ apples in air and
CA storage and MCP treated apples in air and CA storage for 9 month storage.

........................................................................................................................... 59

Table 2.2. Normalized difference in lightness of apples after 3, 5, 7 and 9 months
in storage for untreated ‘Jonagold’ apples in air and CA storage and MCP treated
apples in air and CA storage. ............................................................................. 61

Table 3.1. Salt solutions used in the study of MCP release and the expected
relative humidity they created at 4 and 22°C .................................................... 119

Table 3.2. Empirical equation used to describe the release profiles of MCP
delivery devices ................................................................................................ 120

Table 3. 3. Experiments performed to evaluate the effect of relative humidity on
the MCP release from the MCP delivery devices ............................................. 122

Table 3.4. Water vapor permeability coefficient of low density polyethylene
(LDPE) and ethylene vinyl acetate (EVA) at 10, 20, and 30°C and activation
energy of the permeation process (Ep) at a relative humidity of approximately
90% .................................................................................................................. 127

Table 3.5. Calculated water vapor permeability coefficient of low density
polyethylene (LDPE) and ethylene vinyl acetate (EVA) at 5 and 22°C ............. 129

Table 3.6. MCP permeability (Pucp), diffusion (Dmcp) and solubility (SMcp)
coefficient of low density polyethylene at 5 and 22°C ...................................... 129

Table 3.7. The regression coefficients and the adjusted r2 of the release profile
for MCP delivery devices for power, modified hyperbola and exponential rise to
maximum functions at 22°C and ~100% RH. .................................................. 131

Table 3.8. The regression coefficients and the adjusted r2 of the MCP release
profile for the molecular encapsulated for power, modified hyperbola and
exponential rise to maximum functions at 5 and 22°C, ~100% RH. ................. 131

xi

Table 3.9. The regression coefficients and the adjusted r2 of the release profile
for MCP controlled release devices for power, modified hyperbola and
exponential rise to maximum functions at 5 and 22°C, ~100% RH. ................. 143

Table 3.10. The regression coefficients and the adjusted r2 of the volume of
MCP released from the molecular encapsulation complex for an exponential rise
to maximum function at 22°C. .......................................................................... 149

Table 3.11. The regression coefficients and the adjusted r2 of the MCP released
from the monolithic devices (LDPE matrix) for a modified hyperbola function at
22°C. ................................................................................................................ 152

Table 3.12. The regression coefficients and the adjusted r2 of the MCP released
from the reservoir devices (EVA membrane) for an exponential rise to maximum
function at 22°C ................................................................................................ 155

Table 3.13. The regression coefficients and the adjusted r2 of the MCP released
from the molecular encapsulation complex for an exponential rise to maximum
function at 5°C .................................................................................................. 158

Table 3.14. The regression coefficients and the adjusted r2 of the MCP released
from the monolithic device (LDPE matrix) for an exponential rise to maximum
function at 22°C ................................................................................................ 159

Table B1. p-value for main effect and interaction of storage condition (storage)
and MCP treatments (MCP) of IEC, °Brix, firmness, L*, a* and b* after 3, 5, 7 and
9 month storage ................................................................................. 171

Table B2. Pairwise comparison of Ln (IEC) between 4 postharvest treatments at
3, 5, 7 and 9 month storage ............................................................................... 172

Table B3. Pairwise comparison of °Brix between 4 postharvest treatments at 3,
5, 7 and 9 month storage ................................................................................... 172

Table B4. PainNise comparison of firmness between 4 postharvest treatments at
3, 5, 7 and 9 month storage ............................................................................... 173

Table B5. Pairwise comparison of L*-value between 4 postharvest treatments at
3, 5, 7 and 9 month storage ............................................................................... 173

Table B6. Pairwise comparison of a*-value between 4 postharvest treatments at
3, 5, 7 and 9 month storage ............................................................................... 174

Table B7. Pairwise comparison of b*-value between 4 postharvest treatments at
3, 5, 7 and 9 month storage ............................................................................... 174

xii

Table B8. p-value for main effect and interaction of storage condition (storage)
and MCP treatments (MCP), antibrowning treatment (AB) and shelf life (time) of
L*, a*, b* and AE of FC apples from apples after 3, 5, 7 and 9 month

storage ............................................................................................................... 175

Table B9. Pairwise comparison of L*-value between 4 postharvest treatments A
(air), AM (Air + MCP), CA (controlled atmosphere storage) and CAM (CA + MCP)
with and without antibrowning agent (AB) at 3, 5, 7 and 9 month

storage ............................................................................................................... 177

Table B10. Pairwise comparison of a*-value between 4 postharvest treatments A
(air), AM (Air + MCP), CA (controlled atmosphere storage) and CAM (CA + MCP)
with and without antibrowning agent (AB) at 3, 5, 7 and 9 month

storage ............................................................................................................... 178

Table B11. PainNise comparison of b*-value between 4 postharvest treatments A
(air), AM (Air + MCP), CA (controlled atmosphere storage) and CAM (CA + MCP)
with and without antibrowning agent (AB) at 3, 5, 7 and 9 month

storage ............................................................................................................... 179

Table B12. Painivise comparison of AE between 4 postharvest treatments A (air),
AM (Air + MCP), CA (controlled atmosphere storage) and CAM (CA + MCP) with
and without antibrowning agent (AB) at 3, 5, 7 and 9 month storage ............. 180

Table B13. p-value for main effect and interaction of storage condition (storage)
and MCP treatments (MCP), antibrowning treatment (AB) and shelf life (time) of
texture of FC apples from apples after 3, 5, 7 and 9 month storage .............. 181

Table B14. Pairwise comparison of texture between 4 postharvest treatments A
(air), AM (Air + MCP), CA (controlled atmosphere storage) and CAM (CA + MCP)
with and without antibrowning agent (A8) at 3, 5, 7 and 9 month storage ...... 182

Table B15. p-value for main effect and interaction of storage condition (storage)

and MCP treatments (MCP) and shelf life (time) of hexyl acetate area response
apples from apples after 3, 5, 7 and 9 month storage ................................. 183

xiii

Table B16. Painrvise comparison of hexyl acetate concentration in the package
headspace of FC apples at the shelf life of 0, 1 and 2 weeks from intact apples
that received 4 postharvest treatments A (air), AM (Air + MCP), CA (controlled
atmosphere storage) and CAM (CA + MCP) at 3, 5, 7 and 9 month

storage ........................................................................................... 184

Table C1. Analysis of variance for calibration equation ............................. 186

Table CZ. T-test results for regression parameters of calibration equation... .186

xiv

LIST OF FIGURES

Figure 1.1 Proposed model for ethylene and MCP action on the ethylene
receptor. M represents metal, L1-5 represent ligand of unknown structure, E
represents ethylene (modified from Sisler and Serek 1997) ................................ 6

Figure 2.1. Internal ethylene content of MCP treated and untreated intact apples
stored in air and controlled atmosphere for 3, 5, 7 and 9 month at 0°C (n=5).
Error bars are «2 standard error. For each storage time, the same letter indicates
no significant difference between postharvest treatments within samples from the
same storage time (p-value > 0.05) .................................................................... 54

Figure 2.2. Total soluble solid, as represented by °Brix, of MCP treated and
untreated intact apples stored in air and controlled atmosphere for 3, 5, 7 and 9
months at 0°C (n=5). Error bars are i standard error. For each storage time, the
same letter indicates no significant difference between postharvest treatments
within samples from the same storage time (p—value > 0.05). ............................ 56

Figure 2.3. Firmness of MCP treated and untreated intact apples stored in air
and controlled atmosphere for 3, 5, 7 and 9 months at 0°C (n=5). Error bars are
i standard error. For each storage time, the same letter indicates no significant
difference between postharvest treatments within samples fromthe same
storage time (p-value > 0.05). ............................................................................ 58

Figure 2.4. Lightness (L*) of apple flesh from MCP treated and untreated apples
stored in air and controlled atmosphere for 3, 5, 7 and 9 months at 0°C (n=5).

Error bars are i standard error. For each storage time, the same letter indicates
no significant difference between postharvest treatments within samples from the
same storage time (p-value > 0.05) .................................................................... 61

Figure 2.5. a*-value of apple flesh from MCP treated and untreated apples
stored in air and controlled atmosphere for 3, 5, 7 and 9 months at 0°C (n=5).
Error bars are i standard error. For each storage time, the same letter indicates
no significant difference between postharvest treatments within samples from the
same storage time (p-value > 0.05) .................................................................... 62

Figure 2.6. b*-value of apple flesh from MCP treated and untreated apples
stored in air and controlled atmosphere for 3, 5, 7 and 9 months at 0°C (n=5).
Error bars are i standard error. For each storage time, the same letter indicates
no significant difference between postharvest treatments within samples from the
same storage time (p-value > 0.05) .................................................................... 63

Figure 2.7. Effect of postharvest treatments after 3 months storage on lightness
(L*) of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05) ............. 65

Figure 2.8. Effect of postharvest treatments after 5 months storage on lightness
(L*) of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05) ............. 66

Figure 2.9. Effect of postharvest treatments after 7 months storage on lightness
(L*) of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05) ............. 67

Figure 2.10. Effect of postharvest treatments after 9 months storage on lightness
(L*) of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4 The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05) ............. 68

Figure 2.11. Effect of postharvest treatments after 3 months storage on a* value
of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05) ............. 69

Figure 2.12. Effect of postharvest treatments after 5 months storage on a* value
of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05) ............. 70

Figure 2.13. Effect of postharvest treatments after 7 months storage on a* value
of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05) ............. 71

Figure 2.14. Effect of postharvest treatments after 9 months storage on a* value
of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05) ............. 72

Figure 2.15. Effect of postharvest treatments after 3 months storage on b* value
of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05) ............. 73

Figure 2.16. Effect of postharvest treatments after 5 months storage on b* value
of flesh of apple slices without antibrowning agent (a) and with antibrowning

xvi

agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05) ............. 74

Figure 2.17. Effect of postharvest treatments after 7 months storage on b* value
of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05) ............. 75

Figure 2.18. Effect of postharvest treatments after 9 months storage on b* value
of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05) ............ '. 76

Figure 2.19. Effect of postharvest treatments after 3 months storage on AE value
of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05) ............. 77

Figure 2.20. Effect of postharvest treatments after 5 months storage on AE value
of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05) ............. 78

Figure 2.21. Effect of postharvest treatments after 7 months storage on AE value
of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05) ............. 79

Figure 2.22. Effect of postharvest treatments after 9 months storage on AE value
of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05) ............. 80

Figure 2.23. Effect of postharvest treatments after 3 months storage on the
texture of flesh of apple slices without antibrowning agent (a) and with
antibrowning agent (b) during the holding period at 5°C (n=4). Error bars are i
standard errors. The same letter indicates no significant difference between
postharvest treatments (p-value > 0.05) ............................................................. 84

Figure 2.24. Effect of postharvest treatments after 5 months storage on the
texture of flesh of apple slices without antibrowning agent (a) and with
antibrowning agent (b) during the holding period at 5°C (n=4). Error bars are i
standard errors. The same letter indicates no significant difference between
postharvest treatments (p-value > 0.05) ............................................................. 85

Figure 2.25. Effect of postharvest treatments after 7 months storage on the
texture of flesh of apple slices without antibrowning agent (a) and with

xvii

antibrowning agent (b) during the holding period at 5°C (n=4). Error bars are i
standard errors. The same letter indicates no significant difference between
postharvest treatments (p-value > 0.05) ............................................................. 86

Figure 2.26. Effect of postharvest treatments after 3 months storage on the
texture of flesh of apple slices without antibrowning agent (a) and with
antibrowning agent (b) during the holding period at 5°C (n=4). Error bars are 1r
standard errors. The same letter indicates no significant difference between
postharvest treatments (p-value > 0.05) ............................................................. 87

Figure 2.27. Effect of postharvest treatments after 3 months storage on area
response from GC-MS of hexyl acetate in the headspace of apple slice packages
during the holding period at 3°C (n=4). Error bars are istandard error. The
same letter indicates no significant difference between postharvest treatments (p-
value > 0.05). ..................................................................................................... 90

Figure 2.28. Effect of postharvest treatments after 5 months storage on area
response from GC-MS of hexyl acetate in the headspace of apple slice packages
during the holding period at 3°C (n=4). Error bars are istandard error. The
same letter indicates no significant difference between postharvest treatments (p-
value > 0.05). ..................................................................................................... 91

Figure 2.29. Effect of postharvest treatments after 7 months storage on area
response from GC-MS of hexyl acetate in the headspace of apple slice packages
during the holding period at 3°C (n=4). Error bars are istandard error. The
same letter indicates no significant difference between postharvest treatments (p-
value > 0.05). ..................................................................................................... 92

Figure 2.30. Effect of postharvest treatments after 9 months storage on area
response from GC-MS of hexyl acetate in the headspace of apple slice packages
during the holding period at 3°C (n=4). Error bars are istandard error. The
same letter indicates no significant difference between postharvest treatments (p-
value > 0.05). ..................................................................................................... 93

Figure 2.31. Principal component analysis (a) and canonical discriminant
analysis (b) of 0 week holding period of slices from intact apple stored for 3
months subjected to the following postharvest treatments: Air storage or control
(A), MCP treatment (AM), CA storage (CA) and MCP treatment + CA storage
(CAM). ................................................................................................................ 97

Figure 2.32. Principal component analysis (a) and canonical discriminant
analysis (b) of 2 week holding period of slices from intact apple stored for 3
months subjected to the following postharvest treatments: Air storage or control
(A), MCP treatment (AM), CA storage (CA) and MCP treatment + CA storage
(CAM). ................................................................................................................ 98

xviii

Figure 2.33. Principal component analysis (a) and canonical discriminant
analysis (b) of 0 week holding period of slices from intact apple stored for 5
months subjected to the following postharvest treatments: Air storage or control
(A), MCP treatment (AM), CA storage (CA) and MCP treatment + CA storage
(CAM). ................................................................................................................ 99

Figure 2.34. Principal component analysis (a) and canonical discriminant
analysis (b) of 2 week holding period of slices from intact apple stored for 5
months subjected to the following postharvest treatments: Air storage or control
(A), MCP treatment (AM), CA storage (CA) and MCP treatment + CA storage
(CAM). .............................................................................................................. 100

Figure 2.35. Principal component analysis (a) and canonical discriminant
analysis (b) of 0 week holding period of slices from intact apple stored for 7
months subjected to the following postharvest treatments: Air storage or control
(A), MCP treatment (AM), CA storage (CA) and MCP treatment + CA storage
(CAM). .............................................................................................................. 101

Figure 2.36. Principal component analysis (a) and canonical discriminant
analysis (b) of 2 week holding period of slices from intact apple stored for 7
months subjected to the following postharvest treatments: Air storage or control
(A), MCP treatment (AM), CA storage (CA) and MCP treatment + CA storage
(CAM). .............................................................................................................. 102

Figure 2.37. Principal component analysis (a) and canonical discriminant
analysis (b) of 0 week holding period of slices from intact apple stored for 9
months subjected to the following postharvest treatments: MCP treatment (AM),
CA storage (CA) and MCP treatment + CA storage (CAM) .............................. 103

Figure 2.38. Principal component analysis (a) and canonical discriminant
analysis (b) of 2 week holding period of slices from intact apple stored for 9
months subjected to the following postharvest treatments: MCP treatment (AM),

CA storage (CA) and MCP treatment + CA storage (CAM) .............................. 104
Figure 3.1. The quasi-isostatic technique used for determining MCP barrier
properties ......................................................................................................... 115
Figure 3.2. An example of typical amount of MCP vs. time plot from quasi-
isostatic permeability experiment ..................................................................... 115
Figure 3.3. The mold used for processing of monolithic devices ..................... 116
Figure 3.4. Monolithic and reservoir devices for MCP release study ............... 118

Figure 3.5. The setup of 920 mL glass jar containing salt solution or water
described in Table 3.1 used for the MCP release study. .................................. 119

xix

Figure 3.6. Differntial scanning calorimetric thermogram of low density
polyethylene (LDPE) and ethylene vinyl acetate (EVA) powder. ...................... 123

Figure 3.7. Thermogravimetric analysis thermogram for low density polyethylene
(LDPE), ethylene vinyl acetate (EVA) and the molecular encapsulation complex
......................................................................................................................... 125

Figure 3.8. Arrhenius plot of water vapor permeability for low density
polyethylene (LDPE) and ethylene vinyl acetate (EVA) in the temperature range
of 10~30°C . The solid lines represent the predicted values and the dash lines
represent the confidence interval. .................................................................... 127

Figure 3.9. The volume of MCP gas permeated through LDPE film during the
MCP barrier property testing at 4 and 22°C. .................................................... 129

Figure 3.10. The experimental release profiles of monolithic devices (LDPE
matrix) when subjected to 22°C and ~100% RH (circle) and the predicted
fraction of MCP released using the power function (solid line), the modified
hyperbola function (dotted line) and the exponential rise to maximum function
(dash-dotted line). The error bar represents standard error. ........................... 132

Figure 3.11. The experimental release profiles of monolithic devices (EVA
matrix) when subjected to 22°C and ~100% RH (circle) and the predicted
fraction of MCP released using the power function (solid line), the modified
hyperbola function (dotted line) and the exponential rise to maximum function
(dash-dotted line). The error bar represents standard error. ........................... 133

Figure 3.12. The experimental release profiles of reservoir devices (LDPE
membrane) when subjected to 22°C and ~100% RH (circle for the intact devices
and triangle for the devices with compromised integrity) and the predicted
fraction of MCP released from the intact device using the power function (solid
line), the modified hyperbola function (dotted line) and the exponential rise to
maximum function (dash-dotted line). The error bar represents standard error.
......................................................................................................................... 1 34

Figure 3.13. The experimental release profiles of reservoir devices (EVA
membrane) when subjected to 22°C and ~100% RH (circle) and the predicted
fraction of fraction of MCP released using power function (solid line), modified
hyperbola function (dotted line) and exponential rise to maximum function (dash-
dotted line). The error bar represents standard error. ..................................... 135

Figure 3.14. The experimental release profiles of molecular encapsulation
complex when subjected to 22°C and ~100°/o RH (circle) and the predicted
values of fraction of MCP released during equilibrium using a linear equation
(solid line). The error bar represents standard error ........................................ 136

XX

Figure 3.15. Comparison of predicted MCP delivery system: molecular
encapsulation complex (long dash), monolithic devices with LDPE matrix (solid
line) and EVA matrix (dotted line) and reservoir devices with LDPE membrane
(medium dash) and with EVA membrane (dash-dotted line). ........................... 137

Figure 3.16. Volume of MCP released from approximately 30 mg of the

molecular encapsulation complex at 5 and 22°C, ~100% RH. The error bar
represents standard error. ................................................................................ 144

Figure 3.17. The experimental MCP release profiles of monolithic devices at 5°C
(white circle) and at 22°C (black circle) and the predicted values of MCP release
using the modified hyperbola function at 5°C (dotted line) and 22°C (solid line).
The error bar represents standard error. .......................................................... 145

Figure 3.18. The experimental MCP release profiles of reservoir devices at 5°C
(white circle) and at 22°C (black circle) and the predicted values of MCP release

using the modified hyperbola function at 5°C (dotted line) and 22°C (solid line).
The error bar represents standard error. .......................................................... 146

Figure 3.19. The experimental data for MCP volume released from the molecular
encapsulation complex at 22°C when subjected to 11% RH (closed circle), 36%
RH (open circle), 53% RH (closed triangle), 75% RH (open triangle), 81% RH
(closed diamond), 85% RH (open diamond), 93% RH (closed square) and
~100% RH (open square). The predicted data based on linear function (11, 36,
53, 75 and ~100% RH) and exponential rise to maximum function (81, 85, 93%
RH) are presented as a solid line. The error bar represents standard error. 148

Figure 3.20. The experimental data for MCP volume released from the
monolithic (EVA matrix) devices at 22°C when subjected to 11% RH (closed
circle), 36% RH (open circle), 53% RH (closed triangle), 75% RH (open triangle)
and ~100% RH (open square). The predicted data are based on linear function
(11, 36, 53, 75) and modified hyperbola (100% RH) and are presented as a solid
line. The error bar represents standard error. ................................................. 150

Figure 3.21. The experimental data for MCP volume released from the
monolithic devices (LDPE matrix) at 22°C when subjected to 11% RH (closed
circle), 36% RH (open circle), 53% RH (closed triangle), 75% RH (open triangle),
85% RH (open diamond), 93% RH (closed square) and ~100% RH (open
square). The predicted data based on a linear function (11, 36, 53 and 75% RH)
and modified hyperbola (85, 93 and 100% RH) are presented as a solid line. The
error bar represents standard error. ................................................................. 151

Figure 3.22. The experimental data for fraction of MCP released from the
monolithic devices (LDPE matrix) at 22°C when subjected to 85% RH (open
diamond), 93% RH (closed square) and ~100% RH (open square). The
predicted data based on modified hyperbola are presented in a solid line. The
error bar represents standard error. ................................................................. 153

xxi

Figure 3.23. The experimental data for MCP volume released from the reservoir
devices (EVA membrane) at 22°C when subjected to 85% RH (open diamond),
93% RH (closed square) and ~100% RH (open square). The predicted data
based on a modified hyperbola are presented as a solid line. The error bar
represents standard error. ................................................................................ 155

Figure 3.24. The experimental data for fraction of MCP released from the
reservoir devices (EVA membrane) at 22°C when subjected to 85% RH (open
diamond), 93% RH (closed square) and ~100% RH (open square). The
predicted data based on a modified hyperbola are presented as a solid line. The
error bar represents standard error. ................................................................. 156

Figure 3.25. The experimental data for volume of MCP released from the
molecular encapsulation complex at 5°C when subjected to 79% RH (closed
diamond), 87% RH (open diamond), 97% RH (closed square) and ~100% RH
(open square). The predicted data based on an exponential rise to maximum
function are presented as a solid line. .............................................................. 158

Figure 3.26. The experimental data for volume of MCP released from the
monolithic device (LDPE matrix) at 5°C when subjected to 85% RH (open
diamond), 93% RH (closed square) and 100% RH (open square). The predicted
data based on an exponential rise to maximum are presented as a solid line. 160

Figure 3.27. The experimental data for fraction of MCP released from the
monolithic device (LDPE matrix) at 5°C when subjected to 85% RH (open
diamond), 93% RH (closed square) and 100% RH (open square). The predicted
data based on an exponential rise to maximum are presented as a solid line. 161

Figure 3.28. The envisioned MCP mass transfer activity in produce — package
system containing MCP controlled release devices ......................................... 163

Figure C1. MCP calibration curve prepared using 1-butadiene. The solid line

represents the predicted value and the dotted lines represent the prediction
interval .............................................................................................................. 186

xxii

INTRODUCTION

1-Methylcyclopropene (MCP), an ethylene antagonist, can help to extend
the storage life and shelf life of horticulture crops. MCP is available
commercially under the trade names EthleIoc® and SmartFreshTM. Ethleloc®
is approved for treatment on flowers and ornamental crops. SmartFreshTM is
approved for uses on apples, melons, tomatoes, pears, avocados, mangoes,
papayas, kiwi fruit, peaches, nectarines, plums, apricots, persimmons, bananas,
and broccoli. The cultural use of MCP on fruits and vegetables is a single
application after harvest. It can be used in place of or in combination with
controlled atmosphere storage (CA). When used alone, its effectiveness is
similar to that of CA. When used in combination, the effect is additive to the
effect of CA. This dissertation relates to MCP in two ways: first, the potential of
MCP-treated apples as a raw material for fresh-cut apples and, secondly,
development of a delivery device to enable a continuous in-package treatment of
MCP.

Fresh-cut apples are increasingly more popular and have potential to
increase the revenue stream for the apple industry. The product is available in
supermarkets and quick serve restaurants. Unlike other apple products, fresh-
cut apples have a shorter shelf life than the raw material, i.e whole apples.
Therefore, fresh-cut apples need to be processed at the time when the apple
slices are required to be in the market. In order to have this product available

year round, apples must be preserved using the appropriate postharvest

1

treatment. One of the objectives of this research is to evaluate how the
postharvest treatments of MCP treatment and CA storage, individually and in
combination, over a period of 9 months storage, affects the subsequent quality of
fresh-cut apple slices.

Several published research papers have described an additional benefit of
repeated and continuous MCP treatment of produce such as apples, tomatoes,
and avocados. Therefore, several attempts have been made to develop a
method to continuously deliver MCP. Most devices are reservoir devices that
contain an active component (MCP) within a rate controlling membrane. MCP is
supplied as a gas, contained within a molecular encapsulated complex, or in a
solvent. To a lesser extent, monolithic devices containing MCP gas or a
molecular encapsulation complex are being developed. Thus, the other objective
of this research is to develop MCP controlled release devices and to evaluate

their release characteristics as a function of temperature and relative humidity.

1 LITERATURE REVIEW

1.1 Introduction

Ethylene is a plant hormone produced by higher plants that regulates the
growth and development of fruits and vegetables. Its major postharvest cultural
use is to induce uniform ripening and improved eating quality. Ethylene
synthesis is also implicated in some defense mechanisms to prevent disorders
and microbial spoilage. Despite its beneficial roles, ethylene also has detrimental
effects that shorten the storage life and shelf life of produce by promoting
senescence (Watkins 2002).

The effect of ethylene can be induced by endogenous and exogenous
ethylene. Endogenous ethylene is produced by the produce itself and the
amount depends on the biology and stage of development of the produce. The
ethylene biosynthesis pathway can be found in elsewhere (Watkins, 2002).
Exogenous ethylene is produced by biotic and abiotic sources external to the
effected plant material. This ethylene can come from several sources in the
produce distribution chain. Wholesale markets typically have a low level of
exogenous ethylene (0.06 pL L") while distribution centers can have a level of
ethylene high have an ethylene level of 0.6-1.4 pL L", which is enough to be
physiologically active. Supermarket stores have the lowest ethylene level (0.02-

0.04 uL L") particularly in the display area. Domestic refrigerators have a

tendency to have high ethylene concentration (0.01-0.6 uL L"). The major

sources of ethylene in domestic refrigerators are from other ripened climacteric
fruits. To a lesser extent, trucks and gas-powered forklift vehicles operating in
the distribution environment can produce some ethylene adding 0.001 — 0.005 pL
L" to the normal ethylene levels (Wills and others 2000). In order to extend the
postharvest life of produce, the negative effects of endogenous and exogenous
ethylene have to be controlled. To achieve this, the distribution chain should be
designed so that exposure to exogenous ethylene is minimized. An alternative is
to use an ethylene antagonist, which can counteract the effects of both
endogenous and exogenous ethylene.

Several compounds are known to be ethylene antagonists but not all of
them are suitable for commercial use. One of the most effective ethylene
inhibitors is a silver ion, usually applied as silver thiosulfate (STS). lt inhibits
ethylene action in a non-competitive manner (Veen 1983). However, due to the
heavy metal content, it cannot be used for edible plant products (Sisler and
Serek 1997).

Sisler and his co-workers (Sisler and Serek 1999) have worked to find
compounds that can inhibit ethylene activity. They have found several ethylene
antagonists including 2,5-norbornadiene (NBD) , trans-cyclooctene,
diazocyclopentadiene (DACP), light-irradiated DACP, 3,3-dimethylcyclopropene
(DMCP), cyclopropene, and 1-substituted cyclopropenes. All compounds have
competitive kinetics for ethylene receptors but some, such as NBD and trans-
cyclooctene, requires continuous exposure because they have a short

dissociation time (Sisler and Serek 1999).

Among the ethylene inhibitors mentioned, cyclopropene and 1-substituted
cyclopropenes are among the most effective. Cyclopropene is not as stable as
the 1-substituted cyclopropene (Sisler and Serek 1997). 1-Methylcyclopropene
(MCP) is the most studied compound and is commercially applied to several
types of produce worldwide. 1-ethylcyclopropene (ECP), 1-propylcyclopropene
(PCP) and MCP cause a similar response on avocado but ECP and PCP require
higher concentrations to obtain the maximal ethylene inhibition effect (Feng and
others 2004). In bananas, the concentration necessary to keep the banana peel
green increases as the size of the substitution group increases up to 3 carbons.
Conversely, the necessary concentration decreases as the size of the
substitution group is increased to 4 carbons or more. The necessary
concentration of 1-substituted cyclopropene with a substitution group of 5 or
more carbons is less than that of MCP. However, at the concentration necessary
to keep banana peel green, 1-nonylcyclopropene and 1-decylcylopropene do not
prevent softening of bananas, which may be a result of low permeation of these
compounds through the banana peel. Another drawback of 1-substituted
cyclopropene with a large substitution group is the significantly longer required
treatment time (Sisler and others 2003).

While companies and scientists are interested in other substituted
cyclopropenes, they are not likely to pursue approval of new compounds. MCP
shows the most commercial potential because of its approval for use with several

plant products. Therefore, the next section focuses only on MCP.

1.2 1-Mothylcyclopropene

1-Methylcyclopropene (MCP) is effectively inhibiting ethylene action by
competing for its receptor. Like ethylene, MCP probably binds to a metal in the
receptor. As currently envisioned, ethylene binds to the receptor causing
electrons to be withdrawn, and resulting in a trans positioned ligand moving away
from the metal. Another ligand consequently moves toward the metal (Figure
1.1). As this happens, ethylene diffuses away from the receptor and the active
complex, which is responsible for several ethylene response, is formed. MCP is
thought to remain bound for a longer period; thus the active complex is not
formed (Sisler and Serek 1997). The effect of MCP is not permanent, as
ethylene response resumes after a certain period of time. This may occurs as a
result of the synthesis of new ethylene receptors or MCP may slowly diffuse from

the ethylene receptors (Cameron and Reid 2001).

 

 

 

 

 

 

InactIve Inactwe Active
L2 L2 L2
l l / L3 z/ L3
L1—M—L3 + + L5 —-—> L17I‘AI-"L5 —-> L1----- -M--- L5 + E
l / I, 9
L4 Ethylene E L4 L4
Inactive InactIve
CH3
L2 i L2
l C l/L3
L1 -——M——L3 + /\ + L5 —> L17M --- L5
i H20 — CH 1’
4
L4 MCP MCP L

 

 

 

Figure 1.1 Proposed model for ethylene and MCP action on the ethylene
receptor. M represents metal, L1-5 represent ligand of unknown structure, E
represents ethylene (modified from Sisler and Serek 1997)

The efficacy of MCP depends on several factors. Factors that have been
identified include MCP concentration, crop type, maturation stage and treatment
duration, temperature, and frequency of treatment. In several crops, research
has shown that the efficacy of MCP increases with increasing MCP concentration
up to a certain level. At a concentration higher than this, no additional MCP
benefit is observed (Jiang and others 1999a; Serek and Sisler 2001; Dong and
others 2002). This concentration level has been established for several crops
and is referred to in this review as “the optimum concentration”. At this
concentration, the amount of MCP present is sufficient to saturate the response
(Cameron and Reid 2001). Different crops have different optimum
concentrations. The required MCP also depends on the treatment duration and
temperature. Lower concentration requires a longer duration (Sisler and others
2003). Treatment at low temperature requires higher concentration, likely
because the binding rate of MCP to the receptors is low. However, at low
temperature, MCP remains effective longer because new receptors are
generated at a lower rate than at high temperature (Sisler and Serek 1997).
Table 1.1 contains a summary of the concentration, treatment duration and

temperature that provides beneficial effects in fruits and vegetables.

Table 1.1 Summary of listing MCP concentration and treatment duration and
temperature that provide beneficial effect to fruits and vegetables (modified from
Blankenship and Dole, 2003)

 

 

 

Scientific name Common Treatment
name Conc,, pl/l Temp, °C Time, hour
Anamas comosus Pineapple 0.1 20 18
Anmona squamosa x Custard apple 25 20 14
Annoma cheimola 1
Arabidopsis - 0.0022 - -
Brassica oleracea Broccoli 1, 12 5, 10, 20 6, 12, 16
B. Rapa var. Chinesis'2 Pak choy 12 10 16
B. Juncea var. foliosa'2 Chinese 12 10 16
mustard
B rapa var. . Choy sum 12 10 16
parachinensis 2
B. Rapa var. nipposinica Mibuna and 12 10 16
mizuna
B rapa. Var. rosulan's Tatsoi 12 10 16
Can'ca papaya"3 Papaya 25 20 14
Coriandrum sativum Coriander 0.05 20 24
Cucumis melo (plants) Melon 0.1 - 0.17
CitruI/us Ianatus Watermelon 0.5 20 18
Citrus paradise Grapefruit - 25 16 (twice)
Citrus spp. Orange 0.1 (fruit), 25 6, 12
50
(petioles)
Daucus carota Carrot 1 20 4

 

Table 1.1 (continued)

 

 

 

Scientific name Common Treatment
name Conc., pl/l Temp, °C Time, hour
Diospyros kaki - 0.3 20 3
Fragaria x ananassa Strawberry 0.005- 20 2-18
0.01 5,
025-05, 2
Hanconia speciosa 90 31 Continuous
Lactuca sativa Lettuce 1, 0.1 6 4
L ycopersicon esculentum Tomato 0.005- 20 2-24
0.007,
0.01-0.02,
0.1 5, 20
L ycopersicon esculentum Tomato 4 mg Growing Overnight
(plants) Ethleloc temperature
powder/L
Malus domestica 'Anna', Apple 0.6-2 0, 5, 10, 15, 7 to 20
'Fuji', 'Golden Delicious', 20-25
'Red Delicious', 'Rome',
'Gala', 'Mclntosh',
'Granny Smith', 'Ginger
Gold', 'Jonagold',
'Empire', 'Law Rome'
Mangifera indica'4 Mango 250 20 14
Musa sp., AAA group, Banana 0.005-0.5, 20-24 6-24
Cavendish subgroup 0.1, 45
Nicotiana attenuate Tobacco 0.03, 1.6- Growing 6
(plants) 18 9, temperature
Ethleloc
powder/L
Persea Americana Avocado 0.0503, 3, 5, 20, 22 6-48
0.45, 25
Pisum sativa (seedlings) Pea 40 - 24
Prunus anneniaca Apricot 1

20 4, 20

 

Table 1.1 (continued)

 

 

 

Scientific name Common Treatment
Conc., ul/l Temp, °C Time, hour
Prunus persica'5 Peach and 0.02, 0.1, . 20-24 4, 18, 24
nectarine 500
Prunus salicina Plum 1, 13, 26, 39 20 6, 20, 24
Pyrus communis Pear 2, 4 2 16
Vignaradiata (leaves) Mung bean 0.06 Ambient 24

 

1 MCP treatment increases decay.

'2 MCP is effective only when exogenous ethylene is present.
'3 MCP increases blemish

" MCP increases stem rots

'5 MCP increases internal browning and reduces juice

1.3 The effect of MCP on fresh fruits and vegetables

The effect of MCP has been studied in several crops in order to maximize
the storage life of produce as well as to understand the role of ethylene in

ripening of fruits and vegetables. Some examples follow in this section.

1.3.1 Apple (Malus Pumila)

Apple is the first crop to which MCP could be applied and then sold for
human consumption. The effect of MCP on this crop has been widely studied.
Most of the studies have focused on how MCP and treatment parameters affect
apples in terms of internal ethylene content, respiration rate, firmness, titratable
acidity, total soluble solids, volatile production and storage disorders. All of the
studies have shown the potential of MCP to delay apple ripening and prolong

storage life. Apples studied include ‘Mclntosh,’ ‘Empire,’ ‘Delicious,’ ‘Law Rome,’

10

‘Granny Smith,’ ‘Red Delicious,’ ‘Fuji,’ ‘Ginger Gold,’ ‘Jonagold,’ ‘Gala,’
‘Braeburn,’ ‘York lmperial,’ ‘Cortland’ and ‘Anna’.

MCP suppresses ethylene production and loss of tissue firmness in apples
(Fan and others 1999a; Fan and others 1999b; Watkins and others 2000; Reed
2002; Lu and Toivonen 2003). The reduction of firmness loss is probably
through inhibiting changes in cell wall degrading enzymes (Rupasinghe and
others 2000). MCP inhibits the increase of failure strain and the reduction of
failure stress, toughness, modulus and shock wave speed, which are
characteristics of texture changes associated with ripening.

The effect of MCP on respiration rate, starch content, total soluble solids
and titratable acidity has been investigated but to a lesser extent than internal
ethylene content and firmness. Young fruits have higher starch content and
titratable acidity than more mature fruits. During maturation, titratable acidity
decreases while starch is converted to sugar, thus increasing the total soluble
solids content. MCP reduced the respiration rate and starch loss rate of
‘Delicious’ but did not influence the change in starch of ‘Ginger Gold,’ ‘Gala’ and
‘Jonagold’ (Fan and others 19993). MCP slowed down the reduction in titratable
acidity in most cultivars evaluated (Fan and others 1999a; Fan and others 1999b;
Watkins and others 2000; Reed 2002; Lu and Toivonen 2003) with the exception
of ‘Mclntosh,’ ‘Empire,’ ‘Delicious,’ ‘Law Rome’ (Watkins and others 2000) and
‘Braebum’ (Reed 2002) during 30-40 weeks in controlled atmosphere (CA)
storage and ‘Gala’ during 28 weeks in normal air storage (Mir and others 2001).

The effect of MCP on the total soluble solids is inconclusive because there have

11

been reports that MCP decreases (Watkins and others 2000), increases (Fan
and others 1999a; Fan and others 1999b) or has no effect (Rupasinghe and
others 2000; DeEll and others 2002; Reed 2002) on the total soluble solids of
even the same cultivars.

Apple aroma is an indicator of eating quality and can be assessed by gas
chromatography or sensory evaluation. Based on the analytical analysis, MCP
treatment reduces the production of ester compounds, which are major
components of apple aroma, but does not change the proportion of the 3 main
ester compounds (butyl acetate, 2-methylbutyl acetate and hexyl acetate) (Lurie
and others 2002). MCP treatment and low oxygen controlled atmosphere
storage are very similar in their effect on volatile production except MCP induces
the suppression of volatile production at a faster rate (Mattheis and others 2001).
Many researchers have hypothesized the mechanism for MCP suppression of
the production of ester volatiles. Research with ‘Fuji’ apples by Fan and Mattheis
(1999) indicates that MCP inhibits either alcohol production or conversion of
alcohols to esters (Fan and Mattheis 1999). Lurie et al. (2002) observed that
MCP inhibits the conversion of alcohol to esters because the alcohol detected in
MCP treated ‘Anna’ apples was higher than in non-treated MCP apples. The
reduced volatile production may also be due to a reduced respiration rate and
apparent limiting of acetyl-CoA, a common precursor of fatty acid biosynthesis, in
treated fruits (Rupasinghe and others 2000).

With regard to sensory evaluation, only one publication was found which

described the effect of MCP on sensory characteristics of ‘Anna’ apples. The

12

sensory evaluation of apples during ripening before and after storage was
performed on various intensities of aroma using a trained panel. Non-treated
and 0.1 pL L" MCP treated apples had greater fruity, ripe and overall aromas but
the preference was toward 1 uL L" MCP treated apples with a less ripe aroma
(Lurie and others 2002). The preference toward apples with higher MCP
concentration treatment may also be a result of retention of apple’s high acidity.

In addition to preserving the eating quality, MCP also helps to retain the
peel color. It maintains the brightness of the red color associated with ‘Delicious’
and ‘Gala’ and suppresses the loss of chlorophyll in ‘Granny Smith’ and ‘Golden
Delicious’ (Mattheis and others 2001; Saftner and others 2003).

MCP influences the development of physiological disorders in stored
apples. The occurrence of superficial scald, induced by conjugated trienes
(autooxidation products of a-farnesene) (Fan and others 1999b) is lower in MCP
treated ‘Law Rome,’ ‘Delicious,’ Granny Smith,’ ‘Fuji’ and ‘Cortland’ apples
because MCP delays and reduces a-farnesene production (Fan and Mattheis
1999; Fan and others 1999b; Watkins and others 2000; DeEll and others 2002;
Reed 2002). In addition, MCP also reduces soft scald, greasiness and core flush
in ‘Fuji’ apples (Fan and others 1999b). Regardless of its beneficial effect, MCP
can increase the incidence of internal browning relating to induced carbon
dioxide injury in ‘Golden Delicious,’ (Mattheis and others 2001) ‘Braeburn’
(Mattheis and others 2001, Reed 2002) and ‘York imperial’ (Reed 2002).
Increasing the time between harvest and MCP treatment may help reduce the

risk of internal browning (Mattheis and others 2001).

13

The effectiveness of MCP on apples depends on the maturity of the fruit
as well as the treatment parameters. The effect of MCP is greater when applied
to fruits at the pre-climacteric stage than the climacteric stage (Watkins and
others 2000; Reed 2002). MCP concentration (0.5 — 2 pL L") affects ethylene
production of some cultivars, such as ‘Law Rome’ and ‘Delicious’, but not in
others, such as ‘Mclntosh’ and ‘Empire’ (Watkins and others 2000). In ‘Anna’
apples, MCP treatments of 0.1 uL L" for 20 hours at 20°C did not reduce
ethylene production, while treating with 1 pL L" reduced internal ethylene content
by 95% (Lurie and others 2002). The optimum MCP concentration has been
established for ‘Mclntosh’ and ‘Delicious’ to be 1 pL L" for 12—18 hours at 20°C
(Fan and others 1999a; Rupasinghe and others 2000). The treatment
temperature influences the required treatment time to obtain the maximum effect.
Six hours is required for a treatment temperature of 13 and 23°C, while nine
hours are required when the treatment is applied at 3°C (DeEll and others 2002).
The storage temperature affects the impact of treatment frequency. At low
temperature, the treatment frequency does not change the MCP response. As
the temperature increases, the beneficial impact from treatment frequency
increases (Mir and others 2001).

There are other postharvest technologies used to extend the storage life
of apples. MCP has the potential to replace or be combined with existing
technologies. Controlled atmosphere storage is a widely used method to extend
the storage life of apples. MCP and controlled atmosphere storage have a

similar effect. Cultivars that respond favorably to controlled atmosphere will

14

respond positively to MCP (Mattheis and others 2001). The combination of MCP
and CA storage resulted in greater inhibition than either treatment alone (Watkins
and others 2000; Reed 2002; Lu and Toivonen 2003).

Methyl jasmonate is a plant growth regulator that can affect climacteric
fruit ripening and volatile production. The ability of MJ to reduce ethylene
production is enhanced when combined with MCP. Both compounds inhibit
volatile production by inhibiting both alcohol production and ester formation but
they affect individual alcohols and esters differently. The inhibition of volatile
production by MCP is a result of inhibition of ethylene production but the MJ

inhibitory mechanism is still unknown.

1.3.2 Apricot (Prunus armeniaca)

MCP did not produce satisfactorily results with ‘Patterson’ and ‘Canonin’
apricots when treated prior to storage. It had no effect on delaying the increase
in soluble solids, reduction of titrable acidity or brown rot development (Dong and
others 2002; Palou and Crisosto 2003). Although MCP slightly delayed the
softening process in an ethylene-free environment, it adversely affected the
‘Patterson’ apricot texture when ethylene was present (Palou and Crisosto 2003).
In addition, it caused an increased incidence of internal browning of ‘Canino’
apricots (Dong and others 2002).

Although the use of MCP to extend the storage life of apricots was not
successful in ‘Canino’ apricots, the application of MCP to extend the post storage
shelf life is promising. When MCP is applied after storage, it delays fruit

softening and reduces internal browning and decay. When MCP is applied after

15

5 day cold storage, it reduces ethylene production and respiration of apricot
during ripening period at room temperature. In contrast, it enhances ethylene
production and does not affect the respiration rate when applied after a long-term
cold storage (30 days) (Dong and others 2002)..

The optimum concentration has not been established for apricots but a
treatment of 1 pL L" MCP at 20°C for 20 hours resulted in fruit with better
firmness and less internal browning and decay than treatment at a lower

concentration (Dong and others 2002).

1.3.3 Avocado (Persea amen’cana)

MCP delays avocado ripening but renders it more susceptible to decay. It
increases the number of days to ripen in ‘Haas’ avocado (Hofman and others
2001) and increases the retention of green color in ‘Simmonds’ avocado (Jeong
and others 2002). Softening in several cultivars of avocado including
‘Simmonds,’ ‘Haas,’ ‘Etinger,’ ‘Reed’ and ‘F uerte’ was delayed by MCP treatment
through the suppression of enzymes associated with the softening process,
including Cx-cellulase and polygalacturonase (Feng and others 2000; Jeong and
others 2002). MCP slightly increases the decay sensitivity of avocado (Hofman
and others 2001).

Chilling injury, expressed as mesocarp browning, can be reduced by MCP
treatment. Browning is the result of oxidation of o-diphenols to o-quinones by
polyphenol oxidase resulting in the formation of a brown pigment. Chilling injury
is more pronounced in the presence of exogenous ethylene and it is ethylene

concentration-dependent. MCP reduces this problem by suppressing polyphenol

16

oxidase activity while exogenous ethylene induces the activity of this enzyme
(Pesis and others 2002).

MCP treatment parameters influences how MCP affects avocado. At a
treatment concentration of 0.45 pL L", an increasing treatment time from 6 to 24
hours resulted in increased MCP effectiveness on ‘Simmonds’ avocado (Jeong
and others 2002). Similar results were also found for ‘Haas’ avocado at
concentrations of 0.1 and 0.3 pL L" when the treatment time increased from 24
to 48 hours. Repeating the treatment after 10 days enhanced the MCP effect
(Pesis and others 2002) because the effect of the first treatment lasts about 2

weeks; the treated fruits then resume normal ripening (Feng and others 2000).

1.3.4 Banana (Musa paradisiacal)

MCP treatment of bananas can affect ethylene and respiration climacteric,
volatile production, skin color, and pulp softening. Without the presence of
exogenous ethylene, MCP delays the onset of respiration and ethylene
climacteric. In the presence of exogenous ethylene, MCP does not affect the
onset of the climacteric stage, but MCP-treated fruit produces less ethylene and
has a lower respiration rate (Golding and others 1998). It delays and reduces
volatile production (Golding and others 1998; Golding and others 1999) by
disruption of the ester formation process. The other undesirable consequence of
MCP treatment is the uneven degreening when MCP treated bananas ripen
(Golding and others 1998; Jiang and others 19993).

As with other fruits, the efficacy of MCP depends on MCP concentration
and treatment duration. The optimum concentration for a 12 hour treatment at

17

20°C was 0.05 pL L". For shorter treatment duration, a higher concentration is
required to obtain a similar effect, i.e. treatment with 0.1 pL L" MCP for 12 hours
gave the same result as 1 pL L" MCP for 1 hour (Jiang and others 1999b). An
optimum concentration of 0.5 uL L" was reported for treatment in 0.03 mm thick
low density polyethylene (LDPE) bags for 24 hours at 20°C (Jiang and others
1999a). The higher MCP concentration needed is due to the loss of MCP
through the bag due to permeation.

The banana maturation stage plays an important role in successful
extension of its storage life when treated with MCP. Treatment during the
preclimacteric stage, or up to 12 hours after climacteric onset delays the start of
ethylene and respiration climacteric and skin color change. MCP application
after 24 hours of the climacteric onset is too late to stop the ripening process
(Golding and others 1998).

The timing of the MCP treatment relative to the timing of the exposure to
exogenous ethylene is of prime importance. In banana, application of exogenous
ethylene is used to induce ripening to attain desirable qualities such as peel color
(bright yellow), a firm pulp texture and a good flavor (Kerbel 2002). The effect of
ethylene on MCP treated fruits improves when the time between MCP treatment
and subsequent ethylene treatment increases (Pathak and others 2003).
However, exposure to exogenous ethylene an improper time causes reduction in
banana storage life. MCP can delay the undesirable effect of exogenous
ethylene if applied no later than 1 day after bananas are subjected to exogenous

ethylene (Jiang and others 1999b).

18

MCP, when combined with other treatments such as modified atmosphere
packaging and controlled atmosphere storage, gives synergistic effects. The
combination of MCP and modified atmosphere packaging slows the softening
process and color change, thus extending the storage life of banana more than
either treatment alone. Fruits which underwent the combination treatment
ripened normally without uneven degreening (Jiang and others 1999a). The
effect of MCP on reducing softening rate is also found when MCP is applied
together with controlled atmosphere storage (60 and 100% oxygen content) or

high temperature storage (Jiang and others 2001a; Jiang and Joyce 2003 ).

1.3.5 Broccoli (Brassica oleracea)

MCP extends the shelf life of broccoli by delaying the yellowing process, in
part by reducing peroxidase and chlorophyllase activities (Gong and Mattheis
2003). In addition, MCP slows down the respiration rate (Fan and Mattheis
2000). It also protects broccoli against exogenous ethylene. The benefit of MCP
treatment is similar to the benefit achieved in low temperature storage (Able and
others 2002). This has practical value in distributing broccoli due to the reduced
low temperature requirement.

MCP treatment of broccoli is effective over a wide range of treatment
parameters and storage conditions, but the efficiency depends on several factors
including the temperature at which MCP is applied, frequency of treatment and
MCP concentration. Treatment at high temperature is more effective than at low
temperature because MCP can better attach to ethylene receptor site at high

temperature (Ku and Wills 1999). However, exposure to high temperature can

19

shorten the shelf life of broccoli and causes physiological damage such as

abscission and rotting (Able and others 2002).

Treatment frequency is another factor that influences the shelf life of
broccoli. A second application (12 IIL L" for 6 hours daily) does not increase the
shelf life of broccoli when compared to a single application at the time of harvest.
More than four additional applications can cause harmful side effects such as
wilting and physiological damage. However, continuous application (12 LIL L",
20 hours daily) helps prolong the shelf life (Able and others 2002).

The effectiveness of MCP treatment is concentration-dependent. The
shelf life of broccoli increases when MCP concentration increases. The optimum
concentration of MCP was reported to be between 1-14 pL L". Ku and Wills
(1999) found that the optimum concentration is 1 pL L" (6 hours at 20°C). In
contrast, Fan and Mattheis found no difference in the yellowing process in the
concentration range of 0.01 - 1 pL L" when treated for 12 hours at 10°C (Fan and
Mattheis 2000). However, too high concentration can have negative effet. MCP
concentration greater than 25 pi. L"resu|ts in red-brown coloring on the florets

(Able and others 2002).

1.3.6 Cherm (Prunus avium)

An MCP concentration of 0.1 — 10 pL L" does not have any effect,
beneficial or adversarial, on cherries, a non-climacteric fruit. Treated and non-
treated ‘Bing’ and ‘Rainier’ have approximately the same color, firmness,

respiration rate, and stem browning disorder (only when not exposed to

20

exogenous ethylene) but the treated fruits had higher ethylene production (Gong
and others 2002). Since ethylene production in non-climacteric is inhibited by

ethylene, MCP promotes ethylene formation by decreasing ethylene action.

1.3.7 Coriander (Coriandrum sativum)

Coriander can benefit from MCP treatment particularly when exposed to
less than ideal storage conditions (high temperature or high exogenous ethylene
concentration). Retaining the chlorophyll and protein content in coriander was
affected by MCP during 6 days storage at 15 and 20°C but not at 5 and 10°C
because coriander has low ethylene sensitivity at the low temperature. MCP
treatment also reduces the accumulation of free amino acids, ion leakage and
ethylene production, but does not affect the respiration rate. The optimum

concentration of MCP for coriander is 0.05 pL L" when treated for 24 hours at

20°C (Jiang and others 2002).

1.3.8 Custard apple (Annona chen'mola)

MCP can delay the ripening of ‘African Pride’ custard apples, both in the
presence or absence of ethylene. However, total soluble solids and titratable
acidity remains unaffected. The effective MCP treatment to delay the ripening
process is 25 pL L" MCP for 14 hours at 20°C. However, at this concentration
the amount of black tips, grey flesh, internal black discoloration and core rot

increases (Hofman and others 2001).

21

1.3.9 Mango (Mangifera indica)

The influence of MCP on total soluble solids and titratable acidity of
mango depends on stage of maturation and cultivars. Total soluble solids for
‘Espada’ and ‘Jasmin’ varieties in the mature green stage (1-25% non-green
surface) is not affected by MCP treatment while that of pre-climacteric (51-75%
non-green surface) mangoes is influenced by MCP treatment. 0.1 pL L" MCP on
preclimacteric mangoes reduced the maximum total soluble solids in ‘Jasmin’
and ‘Rosa’ while increasing these components in ‘Espada’ (Silva and others
2004). MCP treated ‘Espada’ and ‘Jasmin’ maintained higher acidity than non-
treated fruits (Silva and others 2004). The total soluble solids and titratable
acidity of ‘Kensington Pride’ are not affected by MCP treatment (Hofman and
others 2001 ).

Skin color, a good indication of ripening, is maintained by MCP treatment.
MCP maintained skin color and external appearance of ‘Jasmin’, ‘Espada’ and
‘Rosa’ because it prevents oxidation of skin pigments, which can result in dulling
of skin color (Silva and others 2004). A desirable effect on skin color change is
also found in ‘Zihua’ mangoes. The treatment of MCP prior to passive modified
atmosphere packaging (polyethylene bag) delays ripening for an additional 10
days at 20°C when compared to mangoes in polyethylene bags with no MCP
treatment (Jiang and Joyce 2000). A desirable effect on skin color was observed
only before the ripening started. Once fruits undergo ripening, the peel color of

treated and untreated fruits are the same (Jiang and Joyce 2000; Silva and

22

others 2004). In contrast, MCP treated ‘Kensington Pride’ mangoes undergo
skin darkening (Hofman and others 2001).

MCP treatment of mangoes can affect the acceleration of ripening by
exogenous ethylene, a common commercial practice. In ‘Kensington Pride,’
MCP had the same effect when applied alone or immediately prior to ethylene
treatment (Hofman and others 2001). This may be desirable as MCP can protect
mangoes from the deleterious effect of exogenous ethylene. However, the fruit
may not have the same quality as non-treated fruit, and the commercial ethylene
ripening process may have to be altered. The duration between MCP treatment
and exogenous ethylene treatment is critical. A longer duration results in faster
ethylene-induced ripening of MCP treated fruits. The more time between the two
treatments is presumed to allow more ethylene binding sites to be synthesized,
and the fruits to regain ethylene sensitivity (Jiang and Joyce 2000).

Mangoes are sensitive to mechanical injury such as impact stress as a
result of improper harvesting or handling. This can accelerate ethylene
production and impair color development. MCP treatment following mechanical
injury slowed down the senescence process in mature green ‘Rosa’ mango by
reducing internal browning, but not in preclimacteric fruit. Preclimacteric MCP
treated fruits that are mechanically injured have a high percentage of internal
browning, fungi infection and water soaked areas, resulting in a fruit condition
which is not acceptable to consumers (Santos and others 2004).

Regardless of the benefits of MCP, its draw back is an increased

sensitivity to storage disorders of treated mangoes. It increases the rot

23

sensitivity in ‘Kensington Pride’. This effect is greater when fruits are treated with
ethylene after MCP treatment (Hofman and others 2001).

MCP concentration and treatment duration are critical factors in the
successful application of MCP. The optimum concentration is 100 pL L" for a 12
hour treatment time or 50 pL L" for 24 hours for ‘Zihua’ mangoes. (Jiang and
Joyce 2000) Other concentrations that have desirable effects on mangoes were
25 pL L" and 14 hours for ‘Kensington Pride’ (Hofman and others 2001) and 0.1
uL L" and 24 hours for ‘Jasmin’, ‘Espada’, and ‘Rosa’ (Silva and others 2004) at
room temperature (20-23°C). The latter two concentrations may not represent

the optimum concentration.

1.3. 10 Nectarine (Prunus persica)

MCP retards firmness loss in ‘Flavortop’ (both ripening after harvest and
ripening after storage), but it caused increased storage disorders during 30 days
in cold storage. This is believed to be a result of ethylene action inhibition. As a
result, pectinesterase and polygalacturonase gene expression are low and
normal cell wall breakdown is slowed down, causing the retardation of loss of
firmness as well as increased storage problems. This suggests that MCP is not
suitable for extension of the storage life of nectarines but has potential to extend
the shelf life of fruits placed in the market directly after harvest (Dong and others

2001)

24

1.3.11 Orange (Citms sinensis)

MCP has little desirable effect on ‘Shamouti’ oranges. The partial
inhibition of the degreening process at a concentration of 0.025 pL L" and total
inhibition of this process above that concentration is beneficial. However, the
use of MCP to arrest degreening has to be done with care because MCP can
increase chilling injury and render oranges more susceptible to decay such as
stem-end rot, caused by Diplodia natalensis, and mold rot, caused by Penicillium
digitatum. It can also increase the accumulation of acetaldehyde and ethyl
acetate in the juice headspace and ethanol in the fruit internal atmosphere. MCP
has no effect on weight loss, firmness, total soluble solids, acid content and

ethylene production (Porat and others 1999).

1.3.12 Pam (Carica papaya)

MCP can effectively increase the time to ripen for papaya by
approximately 3-fold with the treatment of 25 uL L" for 14 hours at 20°C.
However, it increases the sensitivity to postharvest disorders including external

blemishes, stem black rots, body black rots, and anthracnose (Hofman and

others 2001).

1.3.13 Pear (Pyrus communis)

The effect of MCP on pears is mainly on their texture and ethylene
production. MCP slows down the softening process in ‘Barlett’ pears that have
started to ripen and completely inhibits this process in ‘D’Anjou’ pears. It also

retards change in mechanical properties of both pears tissues (Baritelle and

25

others 2001). In ‘La France’ pears, MCP treatment prior to climacteric onset
inhibits the climacteric peak and softening process. When treated after the
climacteric onset, MCP suppressed ethylene production and loss of firmness
(Hiwasa and others 2003).

The effect of MCP concentration on pear responses has not been
published. Treatment concentrations that have beneficial effects are 2 pL L" for

16 hours for ‘Barlett’ and ‘d’Anjou’ (Baritelle and others 2001) and 20 pL L" for

12 hours for ‘La France’ at 20°C (Hiwasa and others 2003).

1.3.14 Persimmon (Dispyros kaki)

MCP does not alter the ethylene production and respiration of persimmon
fruit during cold storage (15°C) and at room temperature after removal from cold
storage. However, it slows the softening process in both conditions. Another
beneficial effect of MCP on persimmon is that it reduces the production of off-
flavor compounds, acetaldehyde and ethanol. The MCP concentration that has a
significant impact on storage and shelf life of persimmons is 1 pL L" or 0.5 pL L"
twice (at the time of harvest and after 20 days in cold storage) at 15°C for 24

hours (Salvador and others 2004).

1.3.15 Pineapple (Ananas comosus)

Although MCP stimulates ethylene production in cold stored pineapples, it
extended the storage life of ‘Queen’ pineapples at a concentration of 0.1 pL L".
It completely eliminates internal browning, a major physiological disorder in the

first two weeks of cold storage. Although internal browning occurs after that, the

26

percent occurrence is reduced and the extent of browning is less than in non-
treated pineapples. MCP also delays shell ripening and the loss rate of ascorbic

acid, total soluble solids and weight (Selvarajah and others 2001).

1.3.16 Plum (Prunus domestica)

The effect of MCP on plums was studied in both climacteric (‘Gulfruby’,
‘Beauty’, ‘Royal Zee’, ‘Laetitia’, ‘Santa Rosa’ and ‘President’) and suppressed
climacteric cultivars (‘Shiro’ and ‘RedRuby’). Suppressed climacteric or very
slow-ripening cultivars produce much less ethylene and have a longer shelf life
than climacteric cultivars (Lelievre and others 1997). Both types of plum
response to propylene (ethylene analog) and MCP differently. MCP-treated
suppressed climacteric cultivars over-ripened and rotted after treatment without
any aroma or ethylene production, but exogenous ethylene treatment can restore
ethylene and aroma production (Abdi and others 1998).

MCP has a more beneficial effect on climacteric cultivars. It delays
ethylene and respiratory climacteric when applied to harvested plums before
storage (Abdi and others 1998; Dong and others 2002; Argenta and others 2003;
Salvador and others 2003) and after cold storage (Dong and others 2002;
Argenta and others 2003; Salvador and others 2003; Valero and others 2004).
The effect of MCP on maximal ethylene production and respiration rate varies
between cultivars. MCP increased maximal ethylene production and respiration
rate in ‘Beauty' and ‘Gulfruby’ at a concentration of 26 pL L" (Abdi and others
1998) and “Royal Zee’ at a concentration of 1 pL L" (Dong and others 2002).
However, it reduced ethylene production and respiration rate in ‘Laetitia’ at a

27

concentration about 0.5 IIL L" (Argenta and others 2003). In ‘Santa Rosa’, 0.5
and 0.75 pL L" of MCP delayed ethylene and the respiration climacteric peak
and reduced the maximum amount of ethylene produced, but did not impact
respiration rate (Salvador and others 2003).

Aroma production in MCP treated ‘Gulfruby’ and ‘Beauty’ plums is
arrested by MCP but could be restored by propylene treatment (Abdi and others
1998). MCP also reduces the production of off-flavor compounds such as
ethanol and acetaldehyde (Salvador and others 2003).

MCP delays the change in skin color, softening, and reduction in titratable
acidity in ‘Royal Zee’ (Dong and others 2002), ‘Laetitia’ (Argenta and others
2003), ‘Santa Rosa’ (Salvador and others 2003) and ’President’ (Valero and
others 2004) plums. It also prevents texture defects such as “gummy and
corklike” in ‘Santa Rosa’ but did not affect their sugar content (Salvador and
others 2003). In contrast, the sugar content in ‘President’ plums is affected by
MCP (Valero and others 2004).

The effect of MCP in plums is concentration-dependent. In ‘Laetitia’,

‘Santa Rosa’ and ‘President’ plums, the optimum concentration is 0.5 pL L"
when treated at 1°C for 24 hours (Argenta and others 2003; Salvador and others
2003; Valero and others 2004). For ‘Beauty’ and ‘Gulfruby’, the optimum
concentration is 13 IIL L" at 20°C for 24 hours, which was the minimum
concentration tested. The actual optimum concentration may be lower than 13

uL L" (Abdi and others 1998).

28

The mode of MCP application plays a role in the efficiency of MCP. For
the same concentration, MCP was found to be more effective when applied after
‘President’ plums were packaged in a perforated carton, a well aerated package,
than when treated in bulk. This may be due to the greater fruit accessibility of

MCP in the well aerated package (Valero and others 2004).

1 .3.17 Rambutan (Nephelium Iappaceum)

MCP extends the shelf life of Rambutan at a concentration of 0.1 pL L". It
enhanced the respiration rate, decreased the ethylene production rate, and
slowed down the loss of titratable acidity and change in lightness (L* value) of the

skin (U-ae and others, 2002).

1.3.18 Strawberry (Fragan’a spp.)

The potential use of MCP in extending the shelf life of strawberries, a non
climacteric fruit that can be affected by exogenous ethylene, is very limited
because it only has a favorable effect on a few varieties and the range of useful
concentration is very narrow. MCP caused reduction in the shelf life of ‘Tioga’,
‘Seascape’ and ‘Parker’ stored at 20°C, due to rotting. For ‘Selva’, 0.005-0.015
pL L" MCP increased the storage life but greater concentration shortened the
shelf life due to decay (Ku and others 1999). Similar results were found for
‘Everest’ strawberry but at a higher concentration (0.1-0.25 “L L"). The higher
concentration resulted in retention of fruit firmness and color, but shortened the
shelf life due to accelerated leak rot, a major disease of this cultivar (Jiang and

others 2001b). It is believed that MCP interferes with strawberry’s natural

29

defense system (Ku and others 1999) as the experiment resulted in a reduction

of phenylalanine ammonia lyase (PAL) activity and phenolic content (Jiang and

others 2001 b).

1.3.19 Tomato (Lycopersicon esculentum)

The shelf life of tomatoes can be extended by MCP treatment, and its
effectiveness depends on several variables. Those that have been studied
include tomato maturation, treatment temperature, MCP concentration, and
frequency of treatment. Based on the delay of color change and firmness of the
flesh, the most effective treatment is the application of MCP to tomatoes at the
mature green stage (Lee 2003; Mir and others 2004). After MCP-treated tomato
is ripened, the taste and aroma are not altered, but the locular gel changes color
much slower than in non-treated fruits (Mir and others 2004).

Treatment parameters have a great influence on MCP effectiveness. The
combination of low temperature and MCP treatment extends the storage life the
most (Lee 2003). The effect of MCP is concentration dependent. The maximum
response is obtained at the concentration of 1 pL L" for a single treatment, which
was the highest concentration tested (Mir and others 2004). Multiple treatment
(once a day) and continuous treatment are more effective than a single treatment

(Lee 2003; Mir and others 2004).

30

1.4 The effect of MCP on fresh-cut produce

MCP research on fresh-cut produce (apples) started in 2002. The number
of publications in this area has risen greatly and expanded to other fresh-cut
produce such as pineapples, tomato, lettuce, and watermelon. The effect of MCP
on fresh-cut produce, arranged alphabetically by produce type is reviewed in this

section.

1.4.1 Fresh-cut apples

Most, if not all, the factors that influence how MCP affects intact fruit play
an important role in how MCP affects fresh-cut apples. In addition, the timing of
MCP treatment relative to the cutting process is important. The quality of fresh-
cut apples also depends on processing conditions such as temperature, the
sharpness of the cutter, and the use of antibrowning and antimicrobial agents.
As a result of these factors, the effect of MCP on fresh-cut apples~ varies. The
differences may be due to the different cultivars and from differences in
processing.

The timing of MCP treatment influences the effect of MCP on fresh-cut
apples. A treatment of 10 pL L" MCP on ‘Golden delicious’ apples prior to
cutting was more effective in delaying deterioration of fresh-cut apples than a 1
pL L" MCP applied to apple slices (Jiang and Joyce 2002). MCP application on
intact fruits was more practical and simpler than its application to fresh-cut apples
because of the stricter sanitation requirements for fresh-cut produce.

When treatment is applied immediately after harvest of ‘Gala’ and

‘Braeburn’ apples, the treated apples (before processing) had lower ethylene

31

content. However, during the shelf life of fresh-cut apples, the ethylene content
increased to approximately the same level as from non-treated apples. MCP did
not affect the respiration rate of ‘Gala’ fresh-cut apples and minimally affected the
respiration rate of ‘Braeburn’, which suggests that wound induced respiration
may not be ethylene—dependent. MCP treated apples are firmer before
processing and retain their firmness better after processing. The effect on flesh
color is different in the two cultivars. MCP had a beneficial effect on ‘Braeburn’
but negative impact on ‘Gala’. The magnitude of the difference is much less in
‘Braeburn’ than in ‘Gala’. In ‘Gala’ the large reduction in L* value is attributed to
secondary browning due to mold growth because MCP may have impaired the
defense mechanism. In contrast, MCP did not affect decay in fresh-cut
‘Braeburn’ apples. MCP did not have any effect on titratable acidity of intact
‘Braeburn’ but did have a positive effect on titratable acidity retention of the
slices. Despite the benefits of MCP, a drawback is reduction of aroma
production (Perera and others 2003), which also happens in treated intact
apples.

The storage time between harvest and MCP treatment and between MCP
treatment and processing influences the quality of fresh-cut apples. As storage
time of intact apples increased, the difference in respiration rate of MCP treated
and non MCP treated Fresh-cut ‘Gala’ increased. However, after processing, the
respiration rate of slices from MCP treated apples increased at a faster rate. The
flesh color of non-treated apples is better than that of MCP treated apples

regardless of the storage time. As the storage time of intact apples increases,

32

however, the difference in the flesh color is lessened (Bai and others 2004). The
storage time between harvest and MCP treatment is a critical factor. MCP had a
more positive effect on ‘Braeburn’ slices from apples, which received MCP
treatment right after harvest, than ‘Pacific Rose’ slices from apples which

received MCP treatment after 3 months storage (Perera and others 2003).

1.4.2 Fresh-gut lettige

MCP has a beneficial effect on minimally-processed lettuce. When
treated before processing, it reduces ascorbic acid loss, leaf yellowing, russet
spotting, respiration rate and ethylene production. The beneficial impact is
greater than that for application of calcium alginate edible coating (a promising
method to extend the shelf life of fresh cut produce). MCP treated and non-
treated lettuce yields fresh cut lettuce with a similar texture while coating lettuce
with calcium alginate can maintain the crispness of cut lettuce better. The

beneficial effect of MCP was achieved by treating lettuce with 0.5 pL L" MCP for

4 hours at 20°C prior to processing (Tay and Perera 2004).

1.4.3 F resh-cut pineapples

Fresh-cut pineapple is another product that can benefit from MCP
treatment. Treatment of intact pineapple fruits reduces the respiration rate and
flesh browning and results in the retention of more ascorbic acid in minimally
processed pineapples, but does not affect firmness or microbial growth. The
greater retention of ascorbic acid is hypothesized to be a reason for reduction in

browning of fresh-cut pineapples. MCP treatment increases the electrolyte

33

leakage but addition of ascorbic acid to the pineapple slices helps reduce the
leakage. The optimum MCP concentration was found to be 1 pL L" (Budu and

Joyce 2003).

1.4.4 Fresh-cut tomato

MCP treatment can benefit fresh-cut tomatoes. Texture retention is
improved by MCP treatment of the sliced tomato (1 pL L‘1 for 24 hours). Factors
influencing its impact include tomato maturity and treatment temperature. The
treatment is more effective in retaining firmness and reducing the incidence of
water soaking when tomato slices are less ripened. The effect is greater when
MCP treatment is performed at 5°C. Wound induced ethylene production is also
greater in MCP treated slices at 5°C but this does not happen when MCP is
applied at 10 and 15°C. The respiration of slices is not affected by MCP

treatment (Jeong and others 2004).

1.4.5 F resh-cpt waiermeiqp

MCP treatment (10 pL L" for 18 hours) of intact watermelon before cutting
did not improve the texture retention of fresh-cut watermelon. Dipping of the
slices in calcium chloride is a better texture preservation method. However, this
treatment activates lipolytic enzymes, such as phospholipase C, phospholipase
D and Iipoxygenases, which are associated with membrane lipid degradation.
The use of MCP treatment together with calcium chloride can inhibit this
activation by shutting down the Ca2*-activation system of lipolytic enzymes (Mao

and others 2004).

34

1.5 MCP commercialization

Commercialization of MCP has been accomplished by F lorallife, Inc.
(Waterboro, SC) under the trade name Ethleloc® for ornamental crops. The
product was approved by the United States Environmental Protection Agency
(EPA) in 1999 (Blankenship and Dole 2003). Most MCP treatment of flowers is
done at the bouquet preparation step, but treatments during trucking and by the
wholesaler are increasing as reflected by the increase in sales in those market
segments (Daly and Schluter 2001). AgroFresh, Inc., a subsidiary of Rohm and
Haas (Spring House, PA), sells MCP under the trade name SmartFreshTM
(Blankenship and Dole 2003) for edible crops. The crops that are approved for
MCP treatments are apples, melons, tomatoes, pears, avocados, mangoes,
papayas, kiwi fruit, peaches, nectarines, plums, apricots, persimmons, bananas,

and broccoli.

1.6 MCP delivery system

MCP gas is relatively unstable due to its reaction potential and possible
explosiveness when compressed. Therefore, it is not safe to commercialize it in
gas form. Molecular encapsulation has been used as means of retaining the
MCP gas to increase safety. In addition, it provides a convenient way to deliver
MCP at a more accurate dosage. Molecular encapsulation agents that can be
used include cyclodextrin, a crown ether, a polyoxyalkylene, a prophorine, a
polysiloxane, a phosphazene and a zeolite (Daly and Kourelis 2000). In
commercial uses MCP (EthyIBloc® and SmartFreshTM) is encapsulated in a-

cyclodextrin. The molecular encapsulation complex can retain MCP for a long

35

time. MCP is released from a-cyclodextrin by adding a buffer containing
potassium hydroxide (Mir and others 2001) or water (Blankenship and Dole
2003). The release rate is relatively high. At standard temperature and
pressure, MCP is released from the complex in approximately 20-30 minutes, but
may take longer at lower temperatures (Blankenship and Dole 2003). This MCP
delivery system is suitable for a one-time MCP treatment.

The disadvantages of powder delivery systems are their dustiness and the
inherent difficulty in accurately measuring small amounts of powder. Moreover,
the powder release system starts to deliver MCP almost immediately upon
contact with a releasing agent. One way to eliminate these disadvantages is the
use of pressure agglomeration of the molecular encapsulation complex to form it
into tablets, wafers, pellets and similar forms. These forms overcome the
potential disadvantages and slow down the release rate when it is first in contact
with a releasing agent (Konstansek 2002).

Several attempts have been made to improve MCP release from a
molecular encapsulation complex more efficiently as shown in several patents.
The addition of water absorbent materials, e.g. sodium polyacrylate and
polysaccharide, and/or deliquescent compounds, e.g. calcium chloride, reduces
the required amount of water to release MCP. A mixture of all three compounds
releases all encapsulated MCP within a day when exposed to high humidity and
within 2 hours when the mixture was dipped in water (Kostansek 2002). The
addition of carbon dioxide generating agents such as sodium bicarbonate and

citric acid to MCP molecular encapsulation complexes results in a much more

36

efficient release of MCP. Incorporating dextrose, an absorbent material, into this
complex does not further improve the release rate, but the addition of benzoic
acid or sodium dodecyl sulfate results in the release of all MCP within 2 hours
(Kostansek and others 2004).

Another MCP delivery system uses absorbing agents. Silica gel and
Tenax-TA (80 mesh) are good absorbing agents. Silica gel has higher MCP
absorption capacity than Tenax-TA. Activated carbon (80/100 mesh) and silica
gel were studied to determine their MCP release rates. No MCP was released
from activated carbon due to its high MCP affinity. Silica gel released MCP
faster at higher humidity (Lee 2003).

An alternative to a solid absorbing agent is a solution containing a lithium
MCP salt. This is achieved by mixing 3-chloro-2-methylpropene into a lithium
diisopropylamide mono(tetrahydrofuran) solution in cyclohexane inside a sealed
tube flushed with argon gas. The chemical mixture yields tetrahydrofuran and a
cyclohexane solvent based solution containing the lithium salt of MCP (Macnish
and others 2004).

The previous MCP forms can be applied to fresh produce in a storage
room. However, storage room systems are usually only available at wholesalers
and others dealing in bulk quantities (Mir and Beaudry 2001). An alternative to
storage room treatment is the treatment in packages. MCP treatment in well-
aerated packages is more effective than in a bulk container (Valero and others
2004). Continuous treatment and repetitive treatment have been shown to

exhibit beneficial effects and to extend the shelf life/storage life of fruits (Mir and

37

others 2001; Able and others 2002; Pesis and others 2002). Several controlled
release delivery systems has been developed to facilitate in-package treatment
and to continuously supply MCP to produce. The controlled release devices
found in the published literature are either reservoir or monolithic devices.

The reservoir device consists of an active component (MCP) contained
within a polymeric film or other materials. The active component can be in the
form of a gas, solvent or powder, as molecular encapsulation complex or
absorbed onto an absorbing agent. For MCP in the gaseous state, gas is
injected into polymer pouches (Sittipod 2003). The release rate of this reservoir
device is the easiest to model. The release rate depends on the transmission
rate of MCP through the polymeric materials. With no leakage, the rate depends
mainly on the concentration of MCP inside the pouch, the surface area of the
pouch, the MCP permeability of the pouch materials, thickness, and
environmental conditions (temperature, relative humidity and pressure).

For MCP-absorbing agents, the absorbing agent is placed in a pouch
made of Tyvek®, Filter paper, LDPE or polyvinyl acetate (PVA). The Tyvek® and
paper pouches containing absorbing agent are exposed to MCP in a closed
system. For LDPE and PVA pouches, MCP is directly injected into the pouch.
Tyvek® and paper pouches release the maximum MCP amount in less than an
hour while LDPE and PVA pouches delay the maximum release to about 5
hours. No release trigger mechanism is required, but humidity in the air

enhances the amount of MCP released from the complex. The effect of relative

38

humidity was greater in Tyvek®, paper and PVA pouches where the water vapor
transmission rate was higher (Lee 2003).

The reservoir device containing a molecular encapsulation complex is the
most studied because of its commercial availability. Molecular encapsulation
complexes need to be in contact with or exposed to a releasing agent. This
releasing agent can be either from an external source or incorporated within the
same reservoir device (same or different compartment). Devices that use
external sources are simpler in construction but their release rate depends on the
environmental conditions, which may not always be controllable.

A reservoir device described in a US Patent (US 6,548,448) consists of a
molecular encapsulation complex laminated between two layers of film without
the presence of release triggering agent. The films used are polyvinyl alcohol
(PVOH) and LDPE. The release rate from PVOH was much slower, about 1/20th
that of LDPE (Konstansek and Edward 2003).

Gas releasing pouches and cartridges are examples of reservoir devices
containing a releasing agent in a separate reservoir. In one device, the pouch
contains molecular encapsulation complex powder and a thin-walled plastic
bubble, containing releasing agent. When the release of MCP is desired, gentle
pressure is applied to the pouch to break the bubble, which allows the releasing
agent to mix with the powder and release MCP gas. The pouch is made up of
two types of polymer, one with high gas permeability and the other one with very
low permeability to gas. The permeable side of the pouch is adhered to the

produce to channel the released MCP to the fruit directly. The device was shown

39

to be effective in inhibiting ripening of banana (Mir and Beaudry 2001). The
cartridge device uses a similar concept, with a different mechanism, to bring the
MCP molecular encapsulation complex into contact with the releasing agent
(Lamola and others 2004).

Reservoir devices that have a releasing agent and a molecular
encapsulation complex in the same compartment and reservoir devices that
contain active agent in the form of MCP solvent are presented in several forms.
Rate controlling materials include a silicone rubber septum, clear PVC, natural
rubber and LDPE. For the same type of device, the amount of MCP released
from 0.09 grams Ethleloc® and 1.8 ml releasing agent (deionised water) was 3-
70 times less than the MCP released from 1 ml MCP solvent. Among all the
devices, the clear PVC tube (6 mm i.d and 1.5 mm thick) sealed with a glass rod
at both ends had the most desirable MCP release characteristics (Macnish and
others 2004).

Another type of MCP controlled release system is monolithic device with
the active agent distributed throughout the rate controlling matrix. One system
uses natural rubber as the rate controlling material and uses MCP gas or MCP
solution as an active compound. The device is created by exposing natural
rubber to MCP gas or immersing it into an MCP solution. This device did not
work well because no MCP was detected (Macnish and others 2004), which
could have been due to either too low or too high affinity between the natural

rubber and MCP. If the affinity is poor, natural rubber will not absorb MCP, thus

40

the initial concentration will be very low or zero. If the affinity is high, MCP will be
held tightly by the rubber, and in either case, it is not effective.

Other rate controlling matrices that are mentioned in US 6,548,448 include
polymeric packaging materials (flexible and rigid), waxes, coated paperbased-
materials and adhesive components. The example shown in the patent includes
waxy cast film (Parafilm), high density polyethylene (HDPE) and wax paper. The
molecular encapsulation complex is mixed into the parafllm solution before the
casting process. The device contains 0.5 gram of the encapsulation complex
and establishes an MCP concentration of greater than 1 pL L" in a 36 liter
chamber in less than 1 hour. For HDPE and the wax paper matrix, the materials
are exposed to a MCP gas concentration of 2206 pL L" for 2 and 5 hours. The
release rate from HDPE is approximately 11 times higher than the rate from wax
paper (Konstansek and Edward 2003).

The only efficacy study of the controlled release devices was done using
reservoir devices (PVC tube). The test was conducted in a carton of Geraldton
waxflower. The device established and maintained a concentration above 0.03
pL L" in a 21 L carton for at least 6 days with the maximum concentration of 1
and 2.5 jiL L" for cartons without and with Geraldton waxflowers, respectively.
However, no MCP was detected when this device was placed in the carton in an
export handling environment for 4.5 days. Two to three devices per carton were
required to reduce weight loss and abscission of floral organ and leaves during
export handling. The greater the number of devices used, the greater was the

MCP protection capacity against exogenous ethylene. The protection offered

41

against exogenous ethylene for 2-3 controlled release devices was comparable
to that of a pulse STS treatment and better than that of a MCP fumigation
treatment prior to export handling. The prevention of floral organ and leaf
abscission by the MCP fumigation treatment was superior to that of the controlled
release devices (Macnish and others 2004).

Placing controlled release devices in packages is less controllable than
using storage rooms. The controlled release devices were less effective in the
carton lined with LDPE than with newsprint because LDPE film is less permeable
to gas and moisture which may have caused higher ethylene accumulation inside

the carton (Macnish and others 2004).

1.7 Conclusion

Researchers have strived to find an ethylene antagonist to slow the
maturation of fresh produce. To date, the most promising ethylene antagonists
are substituted cyclopropenes. MCP is a compound in this category that is being
used because of its commercial availability. It can be used with fresh and
minimally processed produce to reduce the effect of ethylene. An undesirable
result for some produce is the compromising of the produce’s defense
mechanism against some microorganisms for some produce. MCP is currently
commercially available in a molecular encapsulation complex powder. Several
attempts have been made to provide an alternative delivery method to facilitate

continuous and in-package MCP treatment.

42

2 THE EFFECT OF POSTHARVEST CONDITIONS ON SUBSEQUENT
QUALITY OF FRESH-CUT APPLES

2.1 Introduction

Fresh-cut produce has become one of the most popular commodities in
grocery stores over the past 10 years (Garrett 2002). Fresh-cut vegetables such
as pre-packaged salads and shredded carrots are very popular with consumers,
owing to their convenience and flexibility of use. The market for fresh-cut fruits
has been slower to develop, which may be attributable to two reasons: first, fruits
are more perishable than vegetables, causing them to have a shorter shelf life
(Warren 2005); and secondly, consumer perception of quality is different for
fresh-cut fruits and vegetables. The desirable flavor of fresh-cut vegetables
usually comes from an accompaniment, such as a salad dressing, while
consumers expect the inherent flavor and textural quality of fresh-cut fruits to be
self standing (Beaulieu and Baldwin 2002). Most research in fresh-cut fruits has
focused on the reduction in browning and not as much on texture and flavor.
Thus, consumers are still apprehensive about buying fresh-cut fruits. This
hesitation contributes to slow market growth of fresh-cut fruits (Kader 2002).

Sales for fresh-cut produce are expected to rise to $15 billion by the end of
2005, from $10 - $12 billion in 2002 - 2003. Despite its slow market
development in the past, fresh-cut fruits are expected to be a significant
contributor to this growth (Harte and others 2004). Sales of fresh cut fruits were
$719 million in 2004 and are expected to reach the $1 billion level in the near

future (Warren 2005).
43

Fresh-cut apples are increasingly more popular and have potential to
increase the revenue stream for the apple industry. Local supermarkets have
started to carry more fresh-cut apple products. They are mostly from a third
party and carry their own SKUs, rather than being processed in-house. Large
quick serve restaurants such as McDonald have included fresh-cut apples in their
menu. Although fresh-cut apples are becoming more available, a survey has
shown that the purchase of apple slices would not replace the whole apple
purchased (Novak 2004). This indicates that fresh-cut apples will create a new
marketing opportunity for the apple industry.

Due to their longer shelf life, apple products such as applesauce or apple
juice can be processed when whole apples are in the stage that results in the
best product. However, this is not the case with minimally processed apples.
Because of their short shelf life, they need to be processed at the time when they
are required to be in the market. In order to have this product available year
round, the whole apples (prior to slicing) must be preserved using appropriate
postharvest treatments.

Controlled atmosphere storage (CA) is a well-established and widely used
postharvest practice to prolong the storage life of whole apples. Lower oxygen
(1-3%) and higher carbon dioxide (0 — 3%) content in CA storage extend the
storage life of apples by inhibiting ethylene action as well as reducing the
respiratory rate. CA also affects other biological processes that are associated
with produce quality (Beaudry 1999). Recently, 1-methylcyclopropene (MCP), an

ethylene action inhibitor, has been commercially used to prolong the storage life

of apples. Like CA, it has a beneficial effect in extending the storage life of
several cultivars of apples. MCP suppresses the loss of firmness (Fan and
others 1999a; Fan and others 1999c; Rupasinghe and others 2000; Watkins and
others 2000; Lu and Toivonen 2003), reduces the rate of starch content reduction
(Watkins and others 2000) and helps to maintain the titratable acidity in some
apple cultivars (Fan and others 1999a; Fan and others 1999c; Lu and Toivonen
2003). Despite these beneficial effects, both CA and MCP cause reduction of
aroma volatiles that are produced by apples (Plotto and others 2000; Lurie and
others 2002) (Perera and others 2003; Tay and Perera 2004). Despite this,
sensory evaluation indicates preference toward MCP-treated apples over non-
MCP-treated apples (Lurie and others 2002).

Fresh-cut processing is considered to be minimal processing; thus, the
quality of fresh-cut apples relies mainly on the intact apples. However, most of
the research with fresh-cut apples has been concerned with selecting the right
preservation technique. Only a limited number of studies have evaluated the
effect of postharvest handling on the subsequent quality of apple slices. Massey
and McLeIIan (1985) observed that apples, upon immediate removal from CA
storage, may not be optimum for processing either in terms of yield or quality of
the finished product (Massey and McLeIIan 1985). Delay in placing fruits in CA
worsens the yield and firmness of fresh-cut apples, particularly when the apples
are harvested late (McLeIIan and others 1990). The oxygen content in the
storage atmosphere affects apples in terms of anaerobic volatile production, flesh

color, and firmness. Apple slices from intact apples in 1 kPa oxygen undergo

45

less browning but lose firmness more quickly than slices from intact apples in
100 kPa 02 atmosphere. However, high oxygen pressure in the storage
atmosphere results in less formation of products associated with off-flavors (Lu
and Toivonen 2000).

The first research on the use of MCP with fresh-cut produce started in
2002. Publications in this area, to-date, include apples (Jiang and Joyce 2002;
Perera and others 2003; Bai and others 2004; Calderon-Lopez and others 2005),
pineapples (Budu and Joyce 2003), tomato (Jeong and others 2004), lettuce
(Tay and Perera 2004) and watermelon (Mao and others 2004). The effect of
MCP on on the subsequent quality of fresh-cut apples is similar in terms of
firmness retention and reduction of volatile production (Perera and others 2003;
Bai and others 2004; Calderon-Lopez and others 2005). The effect on flesh
browning is inconsistent between cultivars. This may be partly due to the
difference in the maturity of fruits at the time of harvest as well as other
processing parameters. The maturity of apple fruits can influence the extent of
enzymatic browning (Prabha and Patwardhan 1985; Lozano and others 1994).

The objective of this study is to determine how MCP treatment and CA
storage, individually and in combination, with storage time affect the quality of
‘Jonagold’ apples both as whole fruits and the subsequent quality (flesh color,

texture and volatile production) of fresh-cut apples.

46

2.2 Materials and Methods
2.2.1 Plant materials

‘Jonagold’ apples were harvested in late September of 2002. At harvest,
the average internal ethylene content of the apples was approximately 0.24 pL L'
1 with an average weight of 175 gram/fruit and 60% redness of the skin. The
apples had a firmness of 81 N, a starch index of 5.7 and 145° Brix. Apples were
then subjected to 4 different postharvest processes: non-MCP treatment in
normal air storage (air or control apples), MCP treatment in normal air storage
(Air + MCP apples), non-MCP treatment in CA storage (CA apples) and MCP
treatment in CA storage (CA + MCP apples). Description of each of these

postharvest treatments is presented in 2.2.2.

2.2.2 MCP treatment and storage concfltjons

Apples were placed in plastic mesh bags (50 apples/bag). Four bags
were placed in a plastic barrel. Prior to tightly sealing the barrel, a small plastic
container with ~ 0.18 g of SmartFreshTM and water was placed in the barrel to
release sufficient MCP to achieve approximately 1 uL L" MCP gas in the 30
gallon barrel headspace. The calculation of the required amount of
SmartFreshTM is presented in Appendix D. The barrel remained sealed for 16
hours at ambient temperature (~20°C). This concentration and storage time
were expected to be sufficient to saturate the ethylene response in the apples
(Fan and others 1999b; Rupasinghe and others 2000). Another four bags of
apples were treated in the same manner but without exposure to MCP gas. After

16 hours, apples were removed from the barrel and placed in a ventilated 5

47

gallon plastic container (25 apples/container) and stored at 0°C for 10 days.
After 10 days, half of the MCP-treated and non-MCP-treated apples were
removed from normal air storage to CA storage of 1.5% Oz and 3% C02. The
other half remained in air storage. The fruits were then removed at 3, 5, 7 and 9
months for evaluation and processing into fresh-cut slices. Whole apple
evaluation included internal ethylene content, total soluble solids, flesh color, and

firmness.

2.2.3 Internal ethylene content

Internal ethylene content (IEC) of intact apples was evaluated by drawing

1 mL of gas from the interior of the apples as described by Mir and others (2001).

2.2.4 Total soluble solids

The total soluble solids in apple juice were measured using a standard

handheld refractometer. The °Brix was recorded.

2.2.5 Firmness

Apple firmness was measured using a drill-stand-mounted Effegi
penetrometer (FT-327; McCormick Fruit Tree Inc., Yakima, WA) with an 11-mm-
diameter probe. Two skin discs of approximately 2.5 cm diameter were removed
from opposite sides of each fruit prior to pressing the probe into a cut surface to a
depth of approximately 8-9 mm. The force required to press the probe into the

apple flesh was recorded as an index of flesh firmness.

48

2.2.6 Flesh color measurement

The flesh color of intact apples was measured immediately after the whole
apples were cut open. The flesh color was measured using a HunterLab
ColorQuest 45°/0° spectrophotometer (Reston, VA) in 45°l0° geometry.
Immediately after cutting apples in half, the apple flesh was placed over a 1 cm
opening and the L*, a* and b* measurements were recorded. These three values
together serve to define the location of any color in the uniform color space. L*
indicates the lightness co-ordinate and it ranges from 0 to 100 with 0 indicating
black and 100 indicating white. a" is the red/green opponent co-ordinates. A
positive value indicates redness while a negative value indicates greenness. b*
is the yellow/blue opponent co-ordinate with a positive value representing

yellowness and a negative value representing blueness (MacDougall 2002).

2.2.7 Fresh-cut apple preparation

Apples taken out of storage were kept at 5°C in air for 24 hours prior to
processing at room temperature. Apples were sliced into 8 wedges and the core
materials of each piece were removed using a sharp knife. The apple slices
were dipped in a 3% commercial antibrowning agent (NatureSealTM; Mantrose-
Haeuser Co., Inc., Westport, CT), whose active ingredient is calcium ascorbate

or deionized water for 15 seconds and pad-dried using paper towel.

2.2.8 The effect of postharvest conition on fle_§h color of fresh-cut apples
After dipping and pad-drying the slices, the flesh color of the cut surface

was measured using the procedure described in 2.2.6. The slices were then

placed on a plastic tray and packaged in resealable LDPE bags, each bag

49

containing 4 slices. The bags were stored at 5°C. Slices were removed from
each bag and flesh color was measured again after 2, 4, 6 and 12 hours and 1,
2, 4, 6, 10 and 14 days or until microbial spoilage was visually observed. After
each measurement the slices were returned to the packages. The experiment
was performed in random order. Four replicates were used for each postharvest
condition. In addition to the the three measurements (L*, a*, and b*), the total
color difference between flesh color at time t and time = 0 (AE*) was calculated

according to the following equation (MacDougall 2002):

 

* i t 2 t It * * 2
A5 = \/(L O’L t) +(a0—at)2+(bo—b t)
where subscript 0 represents the value at time = 0 and the subscript t represents

the value at any time t.

2.2.9 The effect of postharvest condition on texture of fresh-cut apples

After dipping and pad-drying, the slices from the same fruit were packed
together in resealable LDPE bags and kept at 5°C. One slice was taken out of
the bag at 1 hour, and then at 7 and 14 days for texture evaluation using a
Texture Management System equipped with a thin blade shear-compression cell
(TMS-90; Food Technology Corporation; VA). Apple slices with known weight
were placed in the chamber of the compression cell. The cell moved downward
at a constant speed of 0.15 cmls. The work to move the shear press through the
slice was recorded in N-cm. The value was normalized using the weight of the
apple slice in grams. This weight-normalized work is reported in N-cm g" as an

indication of texture. The higher the value, the greater the firmness. The

50

experiment was performed in random order. Four replications were used for

each postharvest treatment.

2.2.10 The effect of postharvest condition on volatile production by
apple slices

This experiment was performed only with slices dipped in the antibrowning
agent. The volatile compounds were analyzed as individual volatiles and total
volatiles. Selected compounds were analyzed using GC-MS and the total
volatiles using an electronic nose. For both analyses, four replicates were used.
To measure a selected volatile, four slices from the same fruit were packed
together in a resealable LDPE bag. An extra heat-seal was set in place below
the resealable seal. This was to ensure an air tight seal. The headspace
volatiles in the bag were collected at 0.5, 7 and 14 days during the holding period
of fresh-cut slices at 3°C using a solid-phase microextraction fiber with 100 pm
polydimethylsiloxane coating (Supelco, PA). The fiber was inserted into the bag
through a silicon septum and to collect volatiles in headspace for 4 minutes at
3°C. The volatiles were desorbed for 3 minutes into a gas chromatograph
(Hewlett-Packard, Agilent, CA) equipped with a time of flight mass
spectrophotometer (FCD-650, LECO Corp, St. Joseph, MI) for detection and
identification of volatiles. Column temperature was initially set at 40°C and then

increased at a rate of 70°C/min to 250°C. The temperature was held constant at

250°C for 2.5 minutes. The hexyl acetate peak areas were recorded as an index

of the amount of volatile ester present.

51

The effect of postharvest treatment on total volatiles was compared using
an electronic nose system (Fox 3000, Alpha-MOS, Toulouse, France). A 1 cm
diameter and 0.5 cm thick disc was cut from an apple slice and sealed in a 10 mL
headspace vial. The vial was placed on a sample tray. The headspace volatiles
were generated for 10 minutes in a 35°C oven having an agitation speed of 500.
A headspace sample of 2.5 mL was taken with an automatic sampler and
injected into a sensor chamber, containing12 metal oxide sensors. The sensor
responses were recorded for 5 minutes. A delay of 5 minutes between each
injection was used to ensure that the sensors had returned to their baseline. The
sensor responses were optimized and analyzed by the acquisition software
(Alpha SOFT version 8.0, Alpha-MOS, Toulouse, France). The electronic nose
was used to measure the total volatiles twice during a 14-day holding period
(3°C), at the beginning and at the end. Both analyses used apple discs from the

same fruits as those used for individual volatile compound analysis.

2.2.1 1 Statistical analysis

The condition of the apples upon removal from storage was analyzed by
two-way analysis of variance (ANOVA) using a “proc mixed” procedure in SAS
(version 8.0, SAS Institute, Inc., Cary, NC). The independent variables were
MCP treatment, storage atmosphere and their interactions. The data were
analyzed separately for each storage time.

The effect of postharvest condition on flesh color and texture of fresh-cut
slices was analyzed by repeated measure design using the “proc mixed”

procedure in SAS. The independent variables were MCP treatment, storage

52

atmosphere, antibrowning treatment, storage time of fresh-cut slices and their
interactions. The data from each storage time (3, 5, 7 and 9 months) were
analyzed separately. The effect of postharvest conditions on individual volatiles
was analyzed using the same method as for flesh color and texture, but the
independent variables did not include the antibrowning agent. The SAS codes
for two-way ANOVA and repeated measurement are presented in Appendix A.
Data from optimized electronic nose sensor responses obtained from 0
and 14 days holding period of apple slices were analyzed using multivariate
analysis: principal component analysis (PCA), which is an unsupervised learning
technique, and canonical discriminant analysis (CDA) which is a supervised

learning technique.

2.3 Results and Discussion

2.3.1 Condition of apples before fresh-cut apple processing
2.3.1.1 lntemal ethylene content (IE C)

Internal ethylene content (IEC) of intact apples was affected by both MCP
treatment and the storage atmosphere (Figure 2.1). A statistical analysis was
performed on Ln (IEC) to minimize the difference in variance of untransformed
IEC data. Control apples had the highest IEC and MCP-treated apples in CA
storage had the lowest IEC throughout 9 months storage. The combination of
MCP treatment and CA storage had an additive effect. This agrees with the
published results on stored ‘Mclntosh,’ ‘Law Rome,’ and ‘Delicious’ apple fruits

(Watkins and others 2000). MCP-treated apples had lower ethylene than CA

53

storage apple after 3 and 5 month storage. After 7 months storage, the IEC of
these apples were comparable. Similar results were also found in ‘Golden
Delicious’ up to 5 months storage (Saftner and others 2003) and in ‘Mclntosh,’
‘Law Rome,’ and ‘Delicious’ up to 6.5-7 months storage (Watkins and others
2000). Between 7 and 9 months in air storage, the IEC of MCP apples increased

greatly while IEC of both CA and CA + MCP apples remained low.

 

 

 

 

 

I: Air a
CZ] Air + MCP

80° ‘ CA {-
E3 CA + MCP

eoo - a

4ooJ-H [i] {1

100v“ Va

Internal ethylene content (”LL")
8‘1:
0'
.\_Ei" °°
I

N
01
r

\\\\\\\\\‘

f“

 

c c c c c

 

 

 

 

 

 

 

 

 

 

O

 

3 months I 5 months ' 7 months ' 9 months

Storage time

Figure 2.1. Internal ethylene content of MCP treated and untreated intact apples
stored in air and controlled atmosphere for 3, 5, 7 and 9 month at 0°C (n=5).
Error bars are i standard error. For each storage time, the same letter indicates
no significant difference between postharvest treatments within samples from the
same storage time (p-value > 0.05).

54

MCP treatment and CA storage inhibits ethylene biosynthesis by
influencing 1-aminocyclopropane-1-carboxylic acid synthase (ACS) and 1-
aminocyclopropane-1-carboxylic acid oxidase (ACO). MCP blocks autocatalytic
ethylene production (Watkins 2002), which is accomplished by binding to
ethylene receptor sites. This inhibits both ACS and ACO activities (Lu and
Toivonen 2003). The ability of CA storage to suppress ethylene inhibition may
be due to the low oxygen level. Ethylene biosynthesis is oxygen-dependent (Mir
and Beaudry 2002) because ACO requires oxygen as one of its substrates
(Watkins 2002). Thus, the reduced oxygen concentration suppresses the activity
of ACO. The sharp rise in IEC of MCP-treated apples in 9 months air storage
may be a result of the diffusion of MCP away from the ethylene receptors or the
formation of new ethylene receptors (Cameron and Reid 2001). This causes
ethylene production to resume. A sharp rise in IEC did not occur in MCP-treated
or untreated apples in CA storage because they were continuously being
exposed to a low oxygen level.

Another interesting observation that can be made from the data shown in
Figure 2.1 is, as the storage time increased, the IEC of CA apples decreased
while the IEC of CA + MCP apples stayed relatively the same. The high IEC of
CA apples at 3 month storage than at other storage times may be due to the
delayed placement of apples in CA storage at the beginning of the experiment.
This was also observed in previous research (McLeIIan and others 1990). For
CA + MCP apples, ethylene production was suppressed by MCP treatment when

the placement of apples in CA storage was delayed.

55

2. 3. 1. 2 Total soluble solids

Total soluble solids, as indicated by °Brix, is a quality index. Since sugar
is the main component in fruitjuice, % soluble solids is used as an indication of
the sweetness of fruits (Kitinoja and Kader 2002). Fruits with higher total soluble
solids content are sweeter. MCP treatment and storage atmosphere have an
effect on °Brix but the effect was different for each storage time (Figure 2.2).
When compared with the value at harvest, °Brix in control apples stayed

relatively the same at 3 months and slightly declined after that. Apples subjected

 

 

 

 

 

 

 

 

 

 

 

 

 

 

20
l:l Air
IZZ] Air+ MCP
13 - CA
m CA+ MCP
b b
16 -
.5
L
to
O
a
14 - a
12 -
10 .
7months

 

Storage time

Figure 2.2. Total soluble solid, as represented by °Brix, of MCP treated and
untreated intact apples stored in air and controlled atmosphere for 3, 5, 7 and 9
months at 0°C (n=5). Error bars are :I: standard error. For each storage time, the
same letter indicates no significant difference between postharvest treatments
within samples from the same storage time (p-value > 0.05).

56

to at least one of the postharvest treatments had equal or greater °Brix than the
control apples of the same storage time. The individual treatment of MCP or CA
storage either increased or had no effect on the total soluble solids. Several
publications had reported that MCP decreases (Watkins and others 2000),
increases (Fan and others 1999a; Fan and others 19990) or has no effect
(Rupasinghe and others 2000; DeEII and others 2002; Reed 2002) on total

soluble solid of even the same cultivars.

2.3.1.3 Firmness

Firmness is a quality index of apples. Reduction in firmness is an
indication of softening, which, if excessive is undesirable. F irmness was strongly
influenced by MCP treatment and storage atmosphere (Figure 2.3). In general,
firmness decreased with storage time. The firmness of control apples was
reduced to approximately the minimum threshold of 53.4 N (12 lb.), as set by the
Washington tree fruit industry (Mir and others 2001), after 3 months storage at
0°C, and below the threshold with further storage time. The firmness of MCP-
treated apples and apples in CA storage was similar for all storage durations.
Combination of MCP treatment and CA storage had the strongest inhibitory effect
on loss of firmness throughout storage. For up to 9 months of storage, the
firmness of apples that received either MCP treatment, CA storage, or the

combination of the two was always higher than the threshold level of 53.4 N.

57

 

 

 

 

 

          
 

     

    

 

 

 

 

 

90 - I: Air
22 Air + MCP
CA
80 - m CA + MCP
g 70 -
E °°‘ “ as §§
L: § §
50 — a
t
40 - §
§
30 x

 

 

 

 

 

 

 

3 months I 5 m nths 7 months i 9 mnths —

Storage time

Figure 2.3. Firmness of MCP treated and untreated intact apples stored in air
and controlled atmosphere for 3, 5, 7 and 9 months at 0°C (n=5). Error bars are
at standard error. For each storage time, the same letter indicates no significant
difference between postharvest treatments within samples from the same
storage time (p-value > 0.05).

The relationship of firmness to the logarithm of IEC was analyzed using
the Pearson correlation to determine the strength and direction of the
relationship. The Pearson correlation coefficient can range from -1 to +1. The
larger the absolute value, the greater the correlation, while the mathematical sign
indicates whether the two data are proportional or inversely proportional. From

this analysis (Table 2.1) the only significant relationship was found with control

apples. The coefficients suggest that the relationship between firmness and the

58

logarithm of IEC was inversely proportional which agrees with the results in other
studies (Watkins and others 2000). However, the lack of significance with the
other treatments disagrees with previous work done by Watkins et al. (2000),
which showed a significant inverse relationship between IEC and firmness of air
and CA storage apples.

The lack of significant relationship between log (IEC) and firmness in
‘Jonagold’ apples receiving at least one of the postharvest treatments may be
due to small changes in IEC and firmness during storage. The data were again
analyzed to look for a correlation between all apples in air storage and in CA
storage. The correlation coefficients were -0.76 (p-value < 0.0001) and -0.49 (p-
value = 0.001) for apples in air and CA storage, respectively. The relationship
was stronger in apples in air storage, which is consistent with Watkin et al (2000).
Another analysis was performed on MCP-treated and non MCP-treated apples
and the correlation coefficients were -0.45 (p-value = 0.004) and -0.68 (p-value <
0.0001), respectively. This indicates a strong relationship between IEC and

firmness in non-MCP treated apples.

Table 2.1. Pearson correlation coefficients and p-values of correlation evaluation
between flesh firmness (N) and log IEC for untreated ‘Jonagold’ apples in air and
CA storage and MCP treated apples in air and CA storage for 9 month storage.

 

 

Postharvest condition Pearson correlation coefficient p-value
Air (control) 050 0.025
Air + MCP -0.34 0.154
CA 0.06 0.784
CA + MCP 0.05 0.845

 

59

2.3.1.4 Flesh color

Flesh color of apples removed from storage after 3, 5, 7 and 9 month
storage was represented by L*, a* and b*. At each storage time, apples had
similar lightness (L') (Figure 2.4). When a difference was detected, control
apples had the lightest flesh color while MCP-treated apples in CA storage had
the darkest color. In order to determine whether this difference was visually
detectable, a normalized difference in lightness for each storage time was
calculated by (AULo) x 100 where AL is the difference in the average lightness
between apples receiving postharvest treatments and control apples from the
same storage time. L0 is the average lightness of control apples. For apples, the
detectable limit of difference is 2.5. Browning is described as “slight browning”
but the apples are still acceptable when the normalized difference is 4.0. Apples
that undergo serious browning will have a normalized difference of about 15
(Laurila and others 1998). The normalized differences of ‘Jonagold’ were less
than the detectable limit except for MCP-treated apples stored in CA atmosphere
for 7 months, whose flesh was described as slightly brown but still acceptable
(Table 2.2).

Apple flesh color can be described as being between the green and red
co-ordinates with slightly more green component because it has a low negative
number for a* (Figure 2.5). The yellow-blue opponents coordinates (b*) indicated
that the flesh was more yellow due to its large positive b* number (Figure 2.6).

Both a“ and b* values had greater variation than lightness. No significant

60

Table 2.2. Normalized difference in lightness of apples after 3, 5, 7 and 9 months
in storage for untreated ‘Jonagold’ apples in air and CA storage and MCP treated
apples in air and CA storage.

 

Storage time,

Normalized difference in lightness

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

months Air (control) Air + MCP CA CA + MCP
3 0.0 0.8 0.6 1.3
5 0.0 0.4 0.5 2.3
7 0.0 1.5 0.4 3.6
9 0.0 0.6 0.1 0.2
95
I: Air
m Air + MCP
90 _ CA
E CA + MCP
a a
854 3 {—83b —:r:—bab aaaa
Ewbc ab c C TI—
1:
80 —
75 -
70 , —
3 months 5 months 7 months 9 months

Storage time

Figure 2.4. Lightness (L*) of apple flesh from MCP treated and untreated apples
stored in air and controlled atmosphere for 3, 5, 7 and 9 months at 0°C (n=5).

Error bars are i standard error. For each storage time, the same letter indicates
no significant difference between postharvest treatments within samples from the
same storage time (p-value > 0.05).

61

 

 

 

 

 

    
      

       

 

 

 

 

 

 

 

 

 

 

 

a I: Air
-4_o - a [2] Air + MCP
CA
a a [:3 CA + MCP
a
-3.5 ~
g b
(U
-3.0 -
<§
§
-2.5 — §
\
\
-2.0 §

 

 

3 months 7 months 9 months

Storage time

Figure 2.5. a*-value of apple flesh from MCP treated and untreated apples
stored in air and controlled atmosphere for 3, 5, 7 and 9 months at 0°C (n=5).
Error bars are 1 standard error. For each storage time, the same letter indicates
no significant difference between postharvest treatments within samples from the
same storage time (p-value > 0.05).

62

30

 

 

 

 

 

:3 Air

IE] Air+MCP
27 - CA a

m CA+MCP “E

a b
a a D
24 - a “i b
8 a a
in a

21 -
18 -
15

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5 months ' 7 months ' 9 months

Storage time

Figure 2.6. b*-value of apple flesh from MCP treated and untreated apples
stored in air and controlled atmosphere for 3, 5, 7 and 9 months at 0°C (n=5).
Error bars are 1r standard error. For each storage time, the same letter indicates
no significant difference between postharvest treatments within samples from the
same storage time (p-value > 0.05).

63

difference was observed between treatments and the control, or among the
treatments after 3, 5, and 7 months in storage. However, after 9 months in
storage, the flesh (control apples) had significantly more red and yellow
components than the flesh of other apples. The increase in redness and

yellowness is an indication of flesh browning (Lozano and others 1994).

2.3.2 The effect of postharvest condition on flesh color of fresh-cut apples

The flesh color at the cut surface of fresh-cut slices Changed during
storage to a brown color as indicated by a reduced L*(lightness) and an
increased a* (redness) and b* (yellowness) values (Lozano and others 1994).
Due to the Change in these measurements, AE at the cut surface also increased.
This was observed in all apple slices to some extent, depending on the apple
storage time before processing as well as the postharvest treatment. Figures 2.7
— 2.22 presents values of L*, a*, b* and AE of the cut surface of fresh-cut slices
during a 14-day holding period at 5°C for apples from 3, 5, 7, and 9 months. The
lines connecting the data points do not represent a browning rate model; They
are only used to increase the ease of differentiating between each treatment.
The statistical analysis and the pairwise comparison are presented in Appendix
B.

From the four parameters used to describe color, the effect of MCP and
CA storage on L*, a* and AE values were similar (with some slight differences)
while this b* value (yellowness) trend was inconsistent. Therefore, the Change in

b* values was not considered in the following discussion.

64

86

 

 

 

 

 

 

 

 

 

 

(a)
84 ~ I Standard error
82 —
80 A
Q
..I
78 —
76 .
+ Aira
_ —o— Air+ MCP b
74
-v- - CAC
-v— CA + MCP d
72 I . I I
86
(b)
84 -
82 -
80 -
I!
_I
78 ~
76 -
+ Air8 b
- —o— Air+ MCP
74
—v - CAc
—v— CA + MCPd
72 1 . . I
o 100 200 300 400
Time (hour)

Figure 2.7. Effect of postharvest treatments after 3 months storage on lightness
(L*) of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05).

65

 

   

 

 

 

 

  

 

 

 

(b)
84 ~ I Standard error
82 -
\
II V\\ \ \O
...l V\\\ \
78 ‘ \‘W~\\\‘:\\
W
76 q
+ Aira
74 _ —o— AIr+IIiICPb
—v~ - CA°
—v— CA+ MCPc
72 T T I T
86
I Standard error
84 4
\ K \O
80 \7\ ‘1 \
_ \ \
a ¥“‘~. F \
-‘ ‘v“~~\\ ‘3
78 -
76 .
+ Aira b
—'v - CA°
—v—— CA+ II/ICPd
72 T l T T
0 100 200 300 400

Time (hour)

Figure 2.8. Effect of postharvest treatments after 5 months storage on lightness
(L*) of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (na). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05).

66

 

86

 

 

 

 

 

 

 

I Standard error
84 4
82 -
/o\
i fig
80 4
:4 \v\ M \
78 ‘ K \
\ \
V V
76 -I \
+ Air3 \ \
74‘ —O—Air+MCPb \
—v - CAC d V
—V‘- CA + MCP
72 T T I r
86
I Standard error
84 -
..O\
82 q \o. \O
\\ \
80 8 V, \ ‘O
I: \\
-‘ \K
78 - v\ \ \
\ \ \ ‘7
\v
76 -
+ Aira
—o— Air+ MCPb
74 -
—v~ - CAC
+ CA + MCPd
72 T I T I
0 100 200 300
Time (hour)

400

(b)

Figure 2.9. Effect of postharvest treatments after 7 months storage on lightness
(L*) of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no

significant difference between postharvest treatments (p-value > 0.05).

67

L*

L*

86

 

 

I Standard error

(a)

 

 

 

(b)

 

 

84 «
0N0 \0\
82 J j \x 0\ o
\ /
$ \ \O /
80 . Y \
V‘V \
\7\ \ \ a
/
78 \ \ _. /
k \
/V
76 d k a / / /
. . x “ ~v/
+ Air: data not available
74 . —o— Air+MCPa
—v - CAb
—v— CA + MCP C
72 I I I I
86
I Standard error
84 — $3 0
o/
82 - \ \
V\ K x / /
\ ‘ z“
80 4 V\ \ \ / / JV
\ TV” /
78 —
76 ~
—0— Air: data not available
—0— Air + MCP a
74 «
—v - CAb
—v— CA + MCP C
72 l I I I
0 100 200 300
Time (hour)

68

400

Figure 2.10. Effect of postharvest treatments after 9 months storage on lightness
(L*) of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4 The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05).

 

   

 

 

  

2
(a)
0 "i / ’7' / /V
13
m
-2 'l I Standard error
+ Aira
4 . —0— Air + MCP ab
' —v - CAab
—v— CA + MCP b
2
(b)
0 .1
II
in
-2 s
IStandard error
+ Aira‘b
4 —0— Air + MCP ab
' ‘ -—v*-I3Aa
—v— CA + MCP b

 

 

 

0 100 200 300 400

Time (hour)

Figure 2.11. Effect of postharvest treatments after 3 months storage on a* value
of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05).

69

 

k (a)

  

 

 

(U
-2 d
IStandard error
+ Aira
4 q —o— Air+ MCPb
° —-v - CA0
—v— CA + MCP b
2

 

(b)

 
  

-2 'l
IStandard error
+ Air
4 —0— Air + MCP
' —v - CA

—v— CA + MCP

 

 

 

I I I I

0 100 200 300 400

Time (hour)

Figure 2.12. Effect of postharvest treatments after 5 months storage on a* value
of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05).

70

 

 

 

 

 

V
/
/
/
.v’ / "
/ / 4’0
0 a
// 42
v’
1'
(U
-2 _
I Standard error
i + Air3
4 . —o— Air + MCPb
' —v - CAa
—v— CA + MCP b
2
0 _
fi
(0
-2 -4
I Standard error
—o— Air3
4 - —0— Air + MCPab
' —v- - CAb
—v— CA + MCP b

 

 

 

I I I

O 100 200

Time (hour)

I

300

(a)

(b)

400

Figure 2.13. Effect of postharvest treatments after 7 months storage on a* value

of flesh of apple slices without antibrowning agent (a) and with antibrowning

agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05).

71

 

 

 

 

 

 

 

(a)
....” ...—- a
....«4 :37,
/ /V“"" 7 K 7“ ‘ V
0 ~ V’ V/
.m )7 O/ ’O/
_2 _ 74/ //
I Standard error
+ Air: data not available
4 fl —0— Air + MCP a
' -v - CAa
—v— CA + MCP b
2
(b)
0 _
/ ’7” “...—fl. j
W/
. 4v
‘“ // / o— — —o
-2 d y /
O /O
500 f I Standard error
5 + Air: data not available
4 _ —0— Air + MCP a
' —v - CAa
—v— CA + MCPa

o 100 200 300 400
Time (hour)
Figure 2.14. Effect of postharvest treatments after 9 months storage on a* value
of flesh of apple slices without antibrowning agent (a) and with antibrowning

agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05).

72

34 (a)

 

 

 

 

 

 

 

 

32 -
30 -
28 -
C
.o
26 -
24 7 IStandard error
+ Aira
22 —0— Air + MCPab
‘ —v - CAa
—v— CA + MCP b
20 r r j 17
34
(b)
32 -
30 ~
28 ~
*
.D
26 -
/
24 4 /V — "V— —"/ / I Standard error
—0— Aira
22 —0— Air + MCPb
‘ l _, . CAD
—V— CA + MCP C
20 I I T I
0 100 200 300 400
Time (hour)

Figure 2.15. Effect of postharvest treatments after 3 months storage on b* value
of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05).

73

34

 

 

 

 

 

 

 

 

 

 

 

(a)
32 -
30 ~
28 4
I:
.o
26 -
24 7 I Standard error
(L + Air3
22 _ —0— Air + MCP b
—v - CAb
—v— CA + MCP a
20 I I I I
34
(b)
32 -
30 e
______ _____ .... .—-—— ...
28 -
To .— -—— =9” ‘ .5
26 -
24 ~ IStandard error
+ Aira
22 —0— Air + MCP a
‘ 4 - CAb
—v— CA 4' MCP C
20 r r r r
0 100 200 300 400

Time (hour)

Figure 2.16. Effect of postharvest treatments after 5 months storage on b" value
of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05).

74

b*

b*

 

34

32‘

30+

28%

26-1

24‘

22-

 

20

/V
/
/
2 /v/ /ii
——-e—»- /

(a)

IStandard error
—e— Air8
—0— Air + MCP b
_'. . CA8
—v— CA + MCP C

 

34

I

 

32d

30~

28-

26-

24-

22‘

 

20

 

(b)

I Standard error
—o— Airab
—0— Air + MCP C
—v - CAa
—v— CA + MCP b

 

 

I

100

I

200

Time (hour)

I

300 400

Figure 2.17. Effect of postharvest treatments after 7 months storage on b*value
of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05).

 

34

 

(a)

 

 

 

 

 

32 d
.... «v ’7'
30 - 7V ,v/ ’V’
/ 7*
28 -1 f I I
II 0/
26 - /'
24 - I Standard error
+ Air: data not available
22 . —o— Air+ MCP a
—v - CAb
—v— CA + MCP C
20 r I I I
34
(b)
32 -
30 -
28 .1 /V‘ \
‘I f“. \ \ \V
k?“ 0’7
24 7 I Standard error
+ Air: data not available
22 1 —o— Air+ MCP 8*
—v- - CAa
—v— CA + MCP a
20 , , T I
0 100 200 300 400
Time (hour)

Figure 2.18. Effect of postharvest treatments after 9 months storage on b* value
of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05).

76

 

 

 

 

 

   
 

 

 

 

14 — (a)
12 - I Standard error
10 4
UJ 8 ‘
<1
6 d
4 d
+ Air8
—0— Air+ MCPb
2 " _.v. . CAab
—v— CA + MCPa°
0 V I I I
14 ~ (b)
12 4 I Standard error
10 —
UJ 8 ‘
<1
6 _ all"
4 _
+ Aira
—0— Air + MCPa
2 - —-v - CA3
—v— CA + MCPa
0 V I I I
0 100 200 300 400
Time (hour)

Figure 2.19. Effect of postharvest treatments after 3 months storage on AE value
of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05).

77

 

 

   

   

 

 

 

 

   

  

 

 

14 ~ (3)
12 - I Standard error
10 J
/ 8' 77:33
Lu 8 " / ’V/ / 0
Q / / / /
6 .1
4 4
+ Air8
—0— Air + MCPa
2 4 —v- - CAb
—v— CA + MCPC
0 W I I I
14 — (b)
12 4 I Standard error
10 -
8 ~ av
”45' 2”!
”9;,
4/
6 - fi/ ‘0
V’ / /
/>7’ /
4 4 /O
+ Aira
—0— Air + MCPa
2 7 —v - CAa
—v— CA + MCPb
0 V I I I
o 100 200 300 400
Time (hour)

Figure 2.20. Effect of postharvest treatments after 5 months storage on AE value
of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05).

78

 

 

 

 

 

 

 

14 ~ (3)
12 2 I Standard errcy
/
10 - / / l
m 8 _ / /
< /’V / /O
m / /
8 - /0’
4 _
+ Aira
—o- Air+ MCPa
2 ‘ —'v - CAb
—v— CA + MCPC
0 V I I I
14 - (b)
12 - I Standard error
10 T / /V
V’ /
/ /'
8 7 /
‘5 / /
/ f
6 - )7/ /o
4 / /
/0/ —e— Aira
—0— Air + MCPa
2 - —v~ - CAb
+ CA + MCPb
0 v T I I
o 100 200 300 400
Time (hour)

Figure 2.21. Effect of postharvest treatments after 7 months storage on AE value
of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05).

79

 

14 . (a)
12 - I Standard error

101 I’VE

‘7’” /V~:\\
// // "‘3';
m 84 //V r
<‘ /
/04
4 J%/
4

+ Air: data not available
—0— Air+ MCPa

 

 

 

 

 

 

 

2 4 _'. . CAb
-V— CA + MCPc
0 V I I I
14 - (b)
12 - I Standard error
10 -
LLI 8 '
Q
8 . W‘ x z.
.u—r‘" \
f /0 \ \V
4 7 // / \ O
0/ + Air: data not available
o/0 748/ —o— Air+ MCPa
2 - —v - CA3
-V— CA + MCP a
0 v I I I
0 100 200 300 400
Time (hour)

Figure 2.22. Effect of postharvest treatments after 9 months storage on AE value
of flesh of apple slices without antibrowning agent (a) and with antibrowning
agent (b) during the holding period at 5°C (n=4). The same letter indicates no
significant difference between postharvest treatments (p-value > 0.05).

80

The major cause of discoloration on the cut surface was enzymatic
browning, particularly during the early stages of the fresh-cut slice holding period.
During this period, the rate of color change was very fast and was reduced
greatly by the addition of antibrowning agent. During the latter part of the
storage, color change occurred at a slower rate and the magnitude of change
with and without antibrowning agent was approximately the same. The change
in color during this period may have been partly due to enzymatic browning but
was probably also affected by desiccation and/or microbial growth.

After 3 months storage, fresh-cut slices from non MCP-treated apples
(control and CA) experienced less discoloration than MCP-treated apples (MCP
and CA + MCP). This was observed regardless of whether antibrowning agent
was used. The effect of MCP on L*, a*, and AE values was less for slices
receiving antibrowning agent.

For apples stored for 5 months, fresh-cut slices with antibrowning agent
which showed the least to the most discoloration were as follows: control, then
air + MCP and CA + MCP. The slices with the most discoloration were those
from CA apples. This was also observed in slices without antibrowning agent,
except that the flesh colors of slices from control and MCP apples were not
significantly different.

For apples stored for 7 months, slices from control apples experienced the
least discoloration, then air + MCP and CA. The slices with the most browning.

were from CA + MCP apples. This trend was noticed in slices with and without

81

antibrowning agent but the difference for apple receiving antibrowning agent was
much less.

After 9 months storage of whole apples, slices with antibrowning agent
that suffered the least to the most discoloration were slices from air + MCP < CA
< CA + MCP. For slices without antibrowning agent, the trend was the same, but
no significant differences were detected between treatments.

Overall, slices from apples in CA storage (MCP-treated and non-MCP-
treated) were more susceptible to discoloration than slices from apples in air
storage except for apples from 3 months storage. Control apples yielded slices
that were the least susceptible to discoloration. For apples from 3 months
storage, MCP-treated apples in air and CA storage were more susceptible than
non MCP-treated apples in the same storage condition.

In general, slices from more ripe fruit underwent less color change than
fruit that received postharvest treatments that reduced ripening. This agrees with
Lozano (1994) who found that overripe ‘Golden Delicious’ apples underwent the
least discoloration when compared to green and mature apples, which had lower
IEC (Lozano and others 1994). Vamos-Vigyazo et al. (1985) observed a 65%
reduction in enzymatic browning after 6 months in storage, where the IEC of
apples increased (Vamos-Vigyazo and others 1985). The lower browning may
be attributed to the reduced PPO activity and total phenolic content in the apples
during ripening. This was found to be the case for ‘Golden Delicious’ and
‘Aumburi’ pulp whose PPO activity and total phenolic content were reduced by

50% and 10%, respectively, as the apples fully ripened (Prabha and Patwardhan

82

1985). Apples in CA storage were more susceptible to browning than apples in
air storage upon cutting into slices. This was also found in fresh-cut ‘Gala’ after 3
month in 1.4% C02 and 3% 02 for both slices treated with and without
antibrowning agent (Beaulieu and Baldwin 2002).

Slices from CA storage and MCP treatment were more susceptible to
enzymatic browning because they were less ripe than apples from air storage.
They were also firmer; therefore, more cellwall may have been broken during
apple slice preparation. Greater discoloration in slices from MCP-treated apples
was found in fresh-cut ‘Gala’ but the authors attributed the discoloration to
microbial spoilage (Perera and others 2003). Contradictory results were found in
fresh-cut ‘Barebum’ from MCP-treated apples, whose flesh color was not
affected by MCP treatment (Bai and others 2004). This may be a result of the
use of an antibrowning agent and good low temperature maintenance, which

could greatly inhibit enzymatic browning.

2.3.3 The effect of postharvest condition on textifl of fresh-cut apples

CA and MCP treatment, individually and in combination, improved the
firmness of intact apples prior to processing. The length of time slices were held
at 5°C did not significantly affect the firmness (Figure 2.23 — 2.26). This result
agrees with that of fresh-cut slices from other cultivars (Calderon-Lopez and
others 2005). The results of statistical analysis are presented in Appendix B.
Apple slice firmness showed the same trend as the intact apple firmness, but the

difference between treatments was more pronounced in the slices.

83

75

 

E Aira (a)
[Z] Air+MCPb
N CA6

[El CA+MCPd

70—
65-
60-
55-
50- i
45- ¢

40-

Work (N.cm.g")

35 -
30 - [f F}
25

75

 

 

 

 

 

 

 

 

:1 Aira b
7°" @AiHMCPb H
CA0

65 ' m CA+MCPd
604
55 .
so —

45-

Work, (N.cm.g")

40‘

35-

30~

 

 

 

 

 

 

 

 

25

 

N W\\V§H

0 1

Time (week)

Figure 2.23. Effect of postharvest treatments after 3 months storage on the
texture of flesh of apple slices without antibrowning agent (a) and with
antibrowning agent (b) during the holding period at 5°C (n=4). Error bars are :
standard errors. The same letter indicates no significant difference between
postharvest treatments (p-value > 0.05).

84

75

 

(a)
70 a :1 Aira
[221 Air+ MCP '3
65 + CAb

131 CA + MCP °

60-
55-

50-

////21+

45~

Work (N.cm.g'1)

40—
35—

30 —
25 , r}

75

 

 

 

 

 

 

 

 

Cl Aira (b)
7° ‘ [21 Air+ MCPb
CAb

65 ‘ [:3 CA + MCPC

60-
55-

50-

    

////1fl*

45‘ \V

Work (N.cm.g")

4o-

35-

30-4

 

 

 

 

 

25

 

 

N

0 1

Time (week)

Figure 2.24. Effect of postharvest treatments after 5 months storage on the
texture of flesh of apple slices without antibrowning agent (a) and with
antibrowning agent (b) during the holding period at 5°C (n=4). Error bars are i
standard errors. The same letter indicates no significant difference between
postharvest treatments (p-value > 0.05).

85

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

75
[:1 Air3 a
7° [ZZAiHMCPb H
CA6
65 ' [E CA + MCP d
so -
E) 55 -
2‘ 50 -
7'5 45
o _
3
4o -
35 -
30 - f [E
25
75
{:1 Aira b
7° m Air+MCPb b( )
m\\ CAC
‘55 “ LE] CA + MCPd
so -
'0? 55 —
E
U
2' so —
7'5 45
o _
3
4o —
35 -
30 -
25
o 1
Time (week)

Figure 2.25. Effect of postharvest treatments after 7 months storage on the
texture of flesh of apple slices without antibrowning agent (a) and with
antibrowning agent (b) during the holding period at 5°C (n=4). Error bars are i
standard errors. The same letter indicates no significant difference between
postharvest treatments (p-value > 0.05).

86

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

75
70 _ l:l Air: data not available (a)
m Air + MCP a
65 _ CA3
S] CA + MCP b
60 -
7°) 55 —
5
z 50 —
3': 45 —
E
40 —
35 -
30 -
25
75
70 g [:1 Air: data not available (b)
m Air + MCP
55 5 CA3
S CA + MCPb
A 60 - %
"'02 55 . §
32
5 45 ‘ VV
2 \ \
\ §
35 5 \
3O - §
25 Q
0 1 2
Time (week)

Figure 2.26. Effect of postharvest treatments after 3 months storage on the
texture of flesh of apple slices without antibrowning agent (a) and with
antibrowning agent (b) during the holding period at 5°C (n=4). Error bars are i
standard errors. The same letter indicates no significant difference between
postharvest treatments (p-value > 0.05).

87

Slices from MCP-treated apples had greater firmness than slices from non
MCP-treated apples. This agrees with the results for firmness of whole fruit
following MCP treatment of ‘Barebum,’ ‘Pacific Rose,’ (Perera and others 2003)
‘Gala,’ (Bai and others 2004) “Golden Delicious,’ (Jiang and Joyce 2002)
‘Empire,’ ‘Delicious,’ ‘ldared,’ ‘Mutsu,’ and ‘Law Rome’ (Calderon-Lopez and
others 2005).

Comparison between individual postharvest treatments showed that slices
from MCP apples had better texture than CA apples up to 7 months storage.
Slices from MCP and CA apples taken from 9 month storage had similar firmness
although the IEC of intact MCP apples was much higher. The combination of
MCP and CA storage had an additive effect in preserving the texture of apples.
Slices from CA + MCP apples had greater firmness than slices from other apples.
In addition to the postharvest treatments, the antibrowning agent also affected
the texture. A significant difference was found only for slices with low firmness.
These slices also had the least enzymatic browning at the cut surface. The
effect of the antibrowning agent on firmness may be attributed to its calcium
content. This was also previously observed in fresh-cut ‘Golden Delicious” slices

because calcium can prevent the softening process (Lee and Smith 1995).

2. 3.4 The effect of postharvest condition on volatiles of fresh-cut apples
Hexyl Acetate

Hexyl acetate is a compound that contributes to the aroma of apples and,
after 5, 7 and 9 months storage, it had the highest concentration among

compounds detected in the package headspace of fresh-cut ‘Jonagold’ apples.

88

In addition, hexyl acetate is responsible for fruity flavor of apples. Because of
these results, hexyl acetate was selected as the target compound. The area
response from GC-MS chromatograms of hexyl acetate (HA) are presented in
Figure 2.27 — 2.30 for fresh-cut slices from apples that had been stored for 3, 5,
7, and 9 months, respectively. The statistical analyses are presented in
Appendix B. The results show that, during the 14 day shelf life of fresh-cut
slices, HA increased after 1 week. It then either leveled off or declined during the
second week of the holding period. This agrees with the volatiles results for
‘Gala’ slices (Bett and others 2000). The effect of postharvest treatment
depended on the storage time of the intact apples. For 3 and 5 months storage,
the effect of MCP treatment and CA storage was not clear. For 3 months
storage, the HA concentration in the package headspace of slices from air +
MCP, CA, CA + MCP apples were the same at both 0 and 1 week shelf life. This
concentration was lower than that of slices from control apples at 0 week but the
same at 1 week shelf life. At 5 months storage, no postharvest treatment or time
in the holding period effect on the concentration of HA in the headspace except
for fresh-cut slices from CA storage, where the HA concentration increased
during the first week but fell back to the same level the second week.

For intact apples stored for 7 and 9 months, postharvest treatments had
greater effect on the HA content than at 3 and 5 months storage. At 7 months,
slices from apples in CA storage (both MCP and non-MCP-treated) produced
more HA than those from apples in normal air storage. The concentration of HA

in the headspace was relatively constant during the 14 days holding period

89

except for CA + MCP apples, whose HA concentration slightly declined. At 9
months storage, MCP-treated apples in air had a greater HA concentration. The
concentration increased slightly during the first week Storage but decreased
during the second week. F resh-cut slices from CA apples had a high
concentration initially, but the concentration decreased to the same level as that

of slices from CA + MCP apples.

 

 

 

 

 

 

1e+8
(2:21 Air
H l2] Air+ MCP H
‘7 CA T
“1" E33 CA + MCP U"
g 2e+6 -
o
o.
(I)
2
g 1e+6 ‘1
<
5e+5 -
0 1

time, week

Figure 2.27. Effect of postharvest treatments after 3 months storage on area
response from GC-MS of hexyl acetate in the headspace of apple slice packages
during the holding period at 3°C (n=4). Error bars are istandard error. The
same letter indicates no significant difference between postharvest treatments (p-
value > 0.05).

90

1e+8

 

 

 

 

 

 

 

 

 

 

 

l:l Air
E Air + MCP
ge+7 _ CA
ESE CA + MCP
8
c 68+7 ‘
c>
CL
(0
9
to
0,3 4e+7 5
< b
abab ab b
2e+7 — $ 8 a a ab ?|_ a
a a
so: i
0 /§ 1 .
0 1 2
time, week

Figure 2.28. Effect of postharvest treatments after 5 months storage on area
response from GC-MS of hexyl acetate in the headspace of apple slice packages
during the holding period at 3°C (n=4). Error bars are istandard error. The
same letter indicates no significant difference between postharvest treatments (p-
value > 0.05).

91

 

1e+8

8e+7 1

6e+7 ~

4e+7 5

Area response

ab

2e+7 -

 

Figure 2.29. Effect of postharvest treatments after 7 months storage on area
response from GC-MS of hexyl acetate in the headspace of apple slice packages

 

 

CZZD.Afi
[D Air + MCP
sass Cfil
m CA + MCP

bc

ab

ab

 

 

time, week

during the holding period at 3°C (n=4). Error bars are istandard error. The

same letter indicates no significant difference between postharvest treatments (p-

value > 0.05).

 

 

 

 

 

 

 

 

 

 

 

1e+8
[:1 Air (Data nov available)
ED Air + MCP
a CA
89*7 ‘ 131 CA + MCP
a)
3 6e+7 - ab
8 /
w /
9 /
g 4e+7 - /
< a
; ed
2e+7 5 éCdCd
/
/
0 r
1 2
time, week

Figure 2.30. Effect of postharvest treatments after 9 months storage on area
response from GC-MS of hexyl acetate in the headspace of apple slice packages
during the holding period at 3°C (n=4). Error bars are :tstandard error. The
same letter indicates no significant difference between postharvest treatments (p-
value > 0.05).

93

Total volatiles

The total volatiles generated from fresh-cut slices were analyzed using
the electronic nose. This instrument utilizes an array of sensors with partial
specificity and an appropriate pattern recognition system to analyze the volatile
profile without separating volatiles into individual components. Electronic nose
responses together with multivariate analysis has the potential to differentiate
aroma from produce of different cultivars, of differing maturity, harvest date and
defects (Young and others 1999; Echeverria and others 2004; Saevels and
others 2004; Berna and others 2005; Tan and others 2005).

Optimized electronic nose sensor responses were analyzed using
principle component analysis (PCA) and canonical discriminant analysis (CDA).
PCA, an unsupervised learning technique, analyzes a set of data without their
corresponding descriptors (Gardner and Bartlett 1992) to identify a set of
variables called principle components (PC) that can explain all or nearly all of the
total data variation. CDA is a supervised learning technique that analyzes a set
of data, for which descriptors are known, to identify the factor that can be used to
distinguish the predefined groups (Silver and Stam 1994).

Figure 3.21 — 3.28 are the PCA and CDA plots of data for slices at 0 and
14 days after processing from apples subjected to postharvest treatment that has
been stored for 3, 5, 7 and 9 months. For all 4 storage times, the combination of
the first and second principal component (PC1 and PC2) was able to explain

more than 95% of the total variation in data. The combination of the first and

94

second discriminant functions (DF1 and DF2) was able to explain more than 95%
of the variation between postharvest treatments.

For slices from 3 month storage apples at 0 Week holding period (Figure
2.31a), the response from control and CA + MCP apples clustered within its own
group while the data from MCP and CA apples clustered together. According to
the distance between each cluster, the volatiles from MCP and CA apples were
more similar to the volatiles from CA + MCP apples than to those from control
apples. From CDA, DF1 accounted for the variation between slices from the
combination of CA + MCP and the rest. DF2 were accounted for the variation
between slices from the control apple slices and CA or MCP apple slices. After
the slices had been held for 17 days (Figure 2.32), electronic nose responses to
all postharvest treatment clustered within its own group.

After 5 months storage of intact apples (Figure 233-234), the headspace
volatile of CA + MCP apples were completely separated from the other
postharvest treatments by PC1 and DF 1. This was observed at both 0 and 14
days apple slice holding period. The control, air + MCP, and CA apple partially
clustered together at 0 day holding period along P02 and DF2. They totally
clustered together at 14 day holding period.

For intact apples stored for 7 months, slices from the individual treatment
(MCP or CA storage) apples were similar but differentiable in P02. At 0 weeks,
the enose response from this group showed a clear difference from the volatile
from the control and CA + MCP (Figure 2.35a). After 2 weeks in storage, the

enose response from individual treatment with MCP and CA storage clustered

95

together more (Figure 2.35b). This group could be separated from CA + MCP
apple slices by PC1 and DF1 and could be separated from control apple by PC2
and DF1.

After 9 months storage, the volatiles profiles in the slices from all apples
receiving postharvest treatment were clearly distinguishable on both PCA and
CDA plots (Figure 2.37-2.38). The enose response from MCP treated apples
and CA storage apples were more similar at 0 week storage than the response
from apples receiving the combination treatment of MCP and CA storage. MCP
and CA storage influences were less pronounced after a 2-week holding period
of apple slices. Each group, however, was still separated from each other and
the separation could mostly be explained by PC1 and DF1.

The difference between enose response after 2 week storage for the
different treatments was less than the difference at the beginning of the holding
period. For most of the intact apple storage time, the enose responses from
control apple slices and CA + MCP were differentiable from slices from MCP
and/or CA storage. This is because MCP treatment and CA storage reduced
apples volatile production(Plotto and others 2000; Lurie and others 2002; Perera
and others 2003; Tay and Perera 2004; Mattheis and others 2001). Fresh-cut
slices from MCP and CA apples had similar overall production of volatiles up to 7
months storage of intact apples. At 9 month storage, the IEC of air + MCP
increased tremendously resulting in a greater difference in enose response
between Air + MCP and CA apples. The combination of MCP treatment and CA

storage had greater effect in slowing down ripening process, thus, the combined

96

 

0.04

 

 

 

 

 

 

 

A A
CAM (a)
002 q CAMCAM A
A
A AM
o\° 0.00 4
'5
N CA
0 -o.02 - CAM AM
0.
-0.04 a CA
'0.06 I I I I I r
-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3
PC1 (97.96%)
6 (b)
A
4 a A
A
_ A C M
:3 2 5AM
5: AM CAM
d o A
(\l
E M CAM
o _2 q AM AM
CA
CACA
-4 _
CA
6 I I I I r I I I I
-8 -6 4 -2 0 2 4 6 8 10 12

DF1 (77.2%)

Figure 2.31. Principal component analysis (a) and canonical discriminant
analysis (b) of 0 week holding period of slices from intact apple stored for 3
months subjected to the following postharvest treatments: Air storage or control
(A), MCP treatment (AM), CA storage (CA) and MCP treatment + CA storage

(CAM).

97

 

0.010

 

 

 

 

 

 

 

AM
CAM
0.005 ~ AM CA
CAM
3 0.000 -l A
3. CAM CAM AM CACA A
W.
O
8 CA A
a -0.005 -
AM
-0.010 —
A
-0.015 . . i r . 7
-0.15 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20
PC1 (99.69%)
2
AM
CA
1 .. CAM
A
A AM
A C
o CAM
"- AM
o
v CA CA
N MCAM
LL _1 _j
0
AM
2 - A
'3 T I I I I I I I I T
-12 -10 -8 -6 -4 -2 0 2 4 6 8 10

DF1 (99.90%)

Figure 2.32. Principal component analysis (a) and canonical discriminant
analysis (b) of 2 week holding period of slices from intact apple stored for 3
months subjected to the following postharvest treatments: Air storage or control
(A), MCP treatment (AM), CA storage (CA) and MCP treatment + CA storage

(CAM).
98

(a)

(b)

 

 

 

 

 

 

 

 

0.008
A (a)
0.006 -l
A

0.004 -
A CAM
\o
o - A
8 0.002 CAM C
9;
8 0.000 - AM A
a. A

AM
-0002 ~
-0.004 “ CA CA AM
CAM
-0.006 t i . .
-0.3 02 -0.1 0.0 0.1 0.2
PC1 (99,92%)
4
(b)
3 _ A
A

2 _
$5 CA
or) 1 2
‘0.
1: A AM A
g 0 - A CAM
0 AM

-1 5

AM
2 - AM3A CA CA
'3 I I I I I I I
6 -4 2 0 2 4 6 8 10

DF1 (98.47%)

Figure 2.33. Principal component analysis (a) and canonical discriminant
analysis (b) of 0 week holding period of slices from intact apple stored for 5
months subjected to the following postharvest treatments: Air storage or control
(A), MCP treatment (AM), CA storage (CA) and MCP treatment + CA storage

(CAM).

99

 

 

 

 

 

 

 

 

0.06
(a)
0.04 ~
C
AM . MM
A 0.02 . AlVCA
32
00 C AM
(0
g 0.00 - 85M CA
S
o_ A
-0.02 - A
CAM
-0.04 - CA
A
'o-m I I I I I I
-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3
PC1 (96.32%)
3
(b)
2 5 CAAM
AM
1 .. ANCA
A AM
39
E. °‘ 08m CA
(31 A
E: 1 « A
D CAM
-2 - CA
A
-3 -(
'4 I I I I I I
-4 -3 -2 -1 0 1 2 3

DF1 (78.24%)

Figure 2.34. Principal component analysis (a) and canonical discriminant
analysis (b) of 2 week holding period of slices from intact apple stored for 5
months subjected to the following postharvest treatments: Air storage or control
(A), MCP treatment (AM), CA storage (CA) and MCP treatment + CA storage
(CAM).

100

 

0.08

 

 

 

 

 

 

 

CA
0.04 . CA
A
A A
°\° 0.02 ~
0‘3
3 0.00 - CAM A
8 CA
a. -0.02 — CAM
CAM C MM
-0.04 - AM
-0.06 — AM
AM
”0.08 f I I T I I
-0.8 -0.6 04 .02 0.0 0.2 0.4 0.6
PC1 (98.04%)
4
AM
AM CA
’3 CA
5\ 4
8 o
t‘ A A C2AM
v A
E -2 —
O CAM ,
CAM
-4 - CAM
-6 I I I I I I I
-10 -6 -4 2 0 2 4 6 8

DF1 (79.69%)

Figure 2.35. Principal component analysis (a) and canonical discriminant
analysis (b) of 0 week holding period of slices from intact apple stored for 7
months subjected to the following postharvest treatments: Air storage or control
(A), MCP treatment (AM), CA storage (CA) and MCP treatment + CA storage

(CAM).

101

(a)

(b)

PC2 (4.30%)

DF2 (4.28%)

 

0.04

 

 

 

 

(b)

 

 

 

15

CA CA
0.02 - AM
CAM AC”; AM
AM
CAM CA
0.00 -
A
. CAM
-0.02 CAM
A
004 -
-0.06 — A
-0.08 I r r r
-0.3 0.2 -0.1 0.0 0.1 0.2
PC1 (95.56%)
3
2 ‘ CA
1 " AM CAM
o - CA
CAM
-1 -
-2- CAM
CAM
-3 -
A
-4 I I I
-10 -5 0 5 10

DF1 (95.36%)

Figure 2.36. Principal component analysis (a) and canonical discriminant
analysis (b) of 2 week holding period of slices from intact apple stored for 7
months subjected to the following postharvest treatments: Air storage or control
(A), MCP treatment (AM), CA storage (CA) and MCP treatment + CA storage

(CAM).

102

 

0.020

(a)
0.015 4 AM

0.010 ~ CAM

0.005 . AM
CA AM

0.000 . CAM
AM

P02 (0.14%)

-0.005 4

-0.010 « EA

-0015 .

 

CA
-0.020 I I I I I I I

-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4
PC1 (99.85%)

 

 

 

('3)
AM

AM

AM CAM

0%

DF2 (2.25%)
O

 

 

 

'6 I I I I
-20 -10 0 10 20 30

DF1 (97.75%)

Figure 2.37. Principal component analysis (a) and canonical discriminant
analysis (b) of 0 week holding period of slices from intact apple stored for 9
months subjected to the following postharvest treatments: MCP treatment (AM),
CA storage (CA) and MCP treatment + CA storage (CAM).

103

 

0.015

 

 

 

 

 

 

 

CA
0.010 -
CAM CA
CA
0.005 -
§
z: CA
3 0.000 -
2:, 084M
-0005 _ CAM
-0.010 .
AMM
AM
“0.015 I I I I T
-0.15 -0.10 -0.05 0.00 0.05 0.10 0.15
PC1 (98.89%)
3
CA
2 ‘ AM
A CA
3 1 ‘ CA
Si CAM
E
O 0 A CA
AM CAM
'2 I I I I f I
8 -4 -2 0 2 4 6 8

DF1 (96.49%)

Figure 2.38. Principal component analysis (a) and canonical discriminant

analysis (b) of 2 week holding period of slices from intact apple stored for 9
months subjected to the following postharvest treatments: MCP treatment (AM),
CA storage (CA) and MCP treatment + CA storage (CAM).

104

(a)

(b)

The combined treatment was expected to suppressed volatile production in the
intact apples more than each individual treatment does. Therefore, the volatiles
production in fresh-cut slices from MCP treated apples in CA storage was

different from apples receiving only one of the individual treatments.

2.4 Summary and Conclusion

MCP treatment and CA storage, individually or in combination, impacted the
quality of intact ‘Jonagold’ apples as well as the subsequent quality of fresh-cut
apple slices. Either MCP treatment or CA storage suppressed ethylene
production similarly up to 7 months. After that ethylene production in MCP
treated apples increased while that of CA apples remained suppressed. None of
the postharvest treatments adversely affected the flesh color of apples at the
time of slice preparation.

The subsequent quality of fresh-cut slices was affected by the postharvest
treatments. Apples subjected to postharvest treatment (MCP, CA, CA + MCP)
were more susceptible to enzymatic browning due to their immaturity. The
firmness of fresh-cut slices depends solely on the firmness of apples at the time
of processing, which was influenced by postharvest treatment. The use of
antibrowning agent significantly reduced flesh discoloration and. The effect of
antibrowning agent was observed only for slices with very low firmness. The
electronic nose response to the volatiles of the slices from MCP apples and CA
apples was very similar. These responses were differentiable from CA + MCP

and control apple slices except for apples stored for 5 months.

105

Postharvest treatments are a significant contributor to the character of intact
apple and the quality of fresh-cut slices. The storage time also interacts with
these treatments. At 3 month storage of intact apples, MCP treatment was the
best among the three treatments for fresh-cut apple processing. MCP treated
apples had the most firmness, while their susceptibility to enzymatic browning
and volatile production were similar to the apples in CA storage. At 5-7 month
storage, MCP-treated apples and apples in CA storage had similar
Characteristics and either one of them could be used as the raw material for
fresh-cut apples. At 9 months storage, MCP treatment was the most suitable
treatment again because the firmness of MCP-treated apples was still greater
than the minimum threshold (53.4 N) and they were less susceptible to
enzymatic browning than slices from the other apples. The combination
treatment of MCP and CA always resulted in apples having more firmness than
other apples. However, greater susceptibility to enzymatic browning and the
compromised volatile production made it not suitable for fresh-cut apples unless

the effective means to prevent enzymatic browning is implemented.

106

3 DEVELOPMENT OF 1-METHYLCYCLOPROPENE CONTROLLED
RELEASE DELIVERY DEVICE

3.1 Introduction

1-Methylcyclopropene (MCP) is a very effective ethylene action inhibitor
that maintains quality and extends the shelf life and storage life of several
varieties of produce by delaying physico-chemical changes related to the
ripening process (Blankenship and Dole 2003). Some varieties of produce that
benefit from MCP treatment are apples (Fan and others 1999; Fan and Mattheis
1999; Watkins and others 2000; Baritelle and others 2001; Crouch 2001;
Selvarajah and others 2001; DeEll and others 2002; Lurie and others 2002),
apricots (Dong and others 2002), avocados (Feng and others 2000; Hofman and
others 2001), bananas (Jiang and others 1999; Jiang and others 2001; Mir and
Beaudry 2001), broccoli (Ku and Wills 1999; Fan and Mattheis 2000; Gong and
Mattheis 2003), coriander (Jiang and others 2002), custard apples (Hofman and
others 2001), mangoes (Jiang and Joyce 2000; Hofman and others 2001),
nectarines (Dong and others 2001), oranges (Porat and others 1999), papayas
(Hofman and others 2001), pears (Baritelle and others 2001; Hiwasa and others
2003), persimmons (Salvador and others 2004), pineapples (Selvarajah and
others 2001), plums (Abdi and others 1998; Argenta and others 2003; Salvador
and others 2003), rambutans (U-ae and others 2002) and tomatoes (Lee 2003;
Mir and others 2004). Commercial MCP treatment is usually a single application
following harvest of the produce and prior to handling and packing. Due to the

explosive nature of MCP gas, MCP is commercially available in a molecular

107

encapsulation complex using or-cyclodextrin as a molecular encapsulation agent.
MCP gas is released from the complex by adding a buffer containing potassium
hydroxide (Mir and others 2001) or water (Blankenship and Dole 2003).

Recent research indicates the potential of continuous and repeated MCP
treatment (Mir and others 2004). The storage rooms used for single bulk
treatment are typically only available at the wholesaler level or other dealing in
bulk quantities (Mir and Beaudry 2001). When such storage rooms are not
available, a sealed package can provide a mean to contain MCP gas. Packaging
can also create a modified atmosphere around the packaged produce. The
combination of modified atmosphere packaging and in-package MCP treatment
increased the shelf life of bananas (Jiang and others 1999). The in-package
treatment can also provide a continuous exposure of the packaged item.
Repeated and continuous MCP treatments have an additional benefit versus a
single MCP treatment because the MCP effect is not permanent. Produce
becomes sensitive to ethylene again after a certain period of time has elapsed.
Apples, tomatoes and avocados can benefit from a repeated and/or continuous
treatment. The storage life of apples was extended with MCP repeated
treatment (once a week) at storage temperatures of 5, 10, 15 and 20°C (Mir and
others 2001). Sequential and continuous treatment reduced the loss of firmness
and color change more than a single application, particularly at an early stage
(Lee 2003; Mir and others 2004). After 10 days in cold storage, a repeated MCP
treatment was found to preserve the firmness of avocado through its shelf life

(Pesis and others 2002).

108

The current commercial MCP delivery system employs a molecular
encapsulation technique to sustain MCP gas in a powder form. The
encapsulation agent is or-cyclodextrin (Blankenship and Dole 2003). The
complex releases all MCP within a very short time once in contact with the
triggering agent (water or potassium hydroxide buffer). This makes it suitable for
a single treatment as in the current commercial practice.

Several controlled release delivery devices have been developed in order
to facilitate in-package and/or continuous MCP treatment. These devices are
either a reservoir (active component contained within a rate controlling
membrane (Zeoli and Kydonieus 1983)) or a monolithic (active component
distributed throughout a rate controlling membrane (Zeoli and Kydonieus 1983))
types. The active component in reservoir device is in the form of a gas (Sittipod
2003), molecular encapsulation complex (Mir and Beaudry 2001; Macnish and
others 2004), sorbed on an absorbing agent (Lee 2003) or in a solvent form
(Macnish and others 2004). The rate limiting membranes include commonly
used polymeric packaging materials (low density polyethylene, polyvinyl acetate,
Tyvek®, PVC), silicon and natural rubber. The active component in monolithic
device is in the form of a gas (Konstansek and Edward 2003; Macnish and others
2004), molecular encapsulation complexes (Konstansek and Edward 2003) and
solvent (Macnish and others 2004). The rate limiting membranes include natural
rubber, polymeric packaging materials, wax paper and waxy cast film.

The release characteristics of monolithic and reservoir devices are

different. In a reservoir device, the release is essentially a permeability process

109

and the release rate is a zero order function (Christie and others 1997). This is
true as long as the concentration of the active component is constant. The

release rates of monolithic devices depend on diffusion and, in some cases,

solubility coefficients. The release rates are inversely proportional tox/fim—e .
However, if the active component is dissolved in the polymer matrix, this
relationship is only valid up to the time when the device releases 60% of the
active component. The release rates beyond that point and the release rate of
reservoir devices when the concentration of the active agent is not constant are
first order(Zeoli and Kydonieus 1983).

The amount or ratio of active ingredient released from the controlled
release device can be described as a function of time either by an empirical or
theoretical relationship. Sinclair and Peppas proposed using a simplified
exponential relationship for slabs, cylinders and spheres (Sinclair and Peppas
1984). Al-Zahrani proposed a modified hyperbola and exponential rise to
maximum functions to describe his monolithic device for release of several
fertilizers from paraffin and polyethylene wax. Modified hyperbola provided the
best fit for his controlled release device (Al-Zahrani 2000).

The objectives of this study are to develop a device that effectively
controls release of MCP from a molecular encapsulation complex and then to

evaluate the effect of temperature and relative humidity on its release of MCP.

110

3.2 Materials and Methods
3.2.1 Polymer rrgtrices

Low density polyethylene (LDPE) and ethylene vinyl acetate (EVA) were
used as polymer matrices for the controlled release device. Low density
polyethylene (MN 722-00, Equistar, Houston, TX) was provided in a powder form
of 50 mesh irregular particles. Ethylene vinyl acetate (MU 760-00, Equistar,
Houston, TX), a copolymer of polyethylene and 20% vinyl acetate, was provided

in a powder form of 35 mesh irregular particles.

3.2.2 Active compound

The active compound, MCP, was bound in an encapsulation agent. The
MCP molecular encapsulation complex is commercially available in powder form
under the trade name SmartFreshTM (Rohm and Haas Company, Philadelphia,
PA). The encapsulation agent used in SmartFreshT“ is a—cyClodextrin.
SmartFreshTM is referred to as the molecular encapsulation complex throughout

the study.

3.2.3 Thermal analysis

Differential scanning calorimetry

The polymer matrix melting temperature was determined by differential
scanning calorimeter (DSC) according to ASTM D3418-03 (ASTM 2003). The
thermogram was analyzed using Universal Analysis Software (TA Instruments,

New Castle, DE) to determine melting temperature.

111

Thermogravimetric analysis

The thermal degradation of polymer matrices, and the molecular
encapsulation complex was studied using a Thermogravimetric analyzer (TGA
2950, TA Instruments, New Castle, DE) according to ASTM D3850-94 (ASTM
2002). The thermogram obtained was analyzed using Universal Analysis
Software (TA Instruments, New Castle, DE) to determine the degradation

temperature.

3.2.4 MCP analvsis

MCP gas was analyzed using a gas chromatograph equipped with a flame
ionization detector (HP 6890, Hewlett Packard Co., Wilmington, DE) and a 30 m
x 0.32 mm x 0.25 pm HP-5 column. The column temperature was kept at
isothermal at 80°C. The run time was 4 minutes. The area responses were
integrated by using Empower software (Waters lnc., Milford, MA). A standard
curve was prepared using 1-butene due to its similarity in chemical structure to
MCP. The procedure for construction of the calibration curve and the actual

calibration curve are presented in Appendix C.

3.2.5 Barrier properties
The barrier properties of LDPE and EVA films to moisture and MCP were

determined. Test specimens were created by compression molding a plastic
sheet (according to the method for processing blank monolithic devices
described in Section 3.2.6). Two plastic sheets were placed on top of each other

and compressed between two metal plates at 110°C for 1 minute and then

112

allowed to cool for 5 minutes before the pressure was released. The sample
thickness was 61 i 3 um. The test specimens were conditioned at 23°C, 50%

RH for at least 24 hours prior to testing.

Moisture barrier

Moisture barrier of the test specimens was determined at 10, 20 and 30°C,
90% RH using a Perrnatran W3/31 (Mocon, Minneapolis, MN). The test samples
were conditioned for 2 hours in the test cell at the test condition prior to testing.
The test was terminated when steady state was obtained. The average water
vapor transmission rate (WVl' R) during the steady state period was used to
calculate the water vapor permeability coefficient (Pwater) using the following

equafion;

K
Pwater = WVTRxA—p

where Ap is the partial pressure difference between the opposite sides of the
permeation cell and E is the thickness of the test specimen. Using the
permeability coefficients at the three temperatures, the activation energy of the
water vapor permeation process was obtained using the Arrhenius equation

(Hernandez and others 2000).

113

MCP bam‘er

MCP barrier properties were tested at 21°C and 5°C at 0% RH using a
quasi-isostatic method (Hernandez and others 2000). The permeation cell is
shown in Figure 3.1. Three ml of MCP stock gas of approximately 2000 0L L'1
was introduced into the high concentration side. The MCP concentration in the
high concentration side was quantified using gas chromatography, as described
in Section 3.2.5. At predetermined intervals, 200 uL aliquots were drawn from
the low concentration cell and quantified in the same manner. For LDPE and
EVA, the sampling intervals were 30 and 10 minutes, respectively. The
experiment was terminated when the difference in concentration between the two
sides of the film was at approximately 10%. The MCP which permeated through
the test specimen was plotted as a function of time (example in Figure 3.2). The
slope (F53) of this plot was used to calculate the MCP permeability (PMcp) using
the following equation:

I
A-Ap

 

PMCP = Fss X

where A is the surface area of the test specimen exposed to the MCP gas, 6 is
the thickness of film specimen, and Ap is the partial pressure difference between
both sides of test specimen. The MCP diffusion coefficient (DMcp) was calculated

as follows (Hernandez and others 2000):

[2
DMCP = a

114

where 0 is the lag time which is the point where the steady state portion extends
to intersect with the time axis (x-axis). The MCP solubility coefficients (SMCp)

were calculated from the following equation (Hernandez and others 2000).

 

p
SMCP = ‘fl
DMCP
. “:3 Sampling port
._ Low concentration chamber ,3 ‘
:__ '3__; Test specimen
. H'°"°°°°°"“?“°“°"°‘"°°‘T _ “it: 2 \ 'niecfion 9°“ ‘0
j . _ ,.._ ..,l,. mu. t-‘c\\f.'"..\‘ - 1111“}.‘1‘15m‘lhu ‘~ ‘- . _ introduce MCP

v , . . q ....._\ I‘lw~]:.~r.‘.,la ...‘v ... - I‘.;?‘ .55} v ~_«. I.) "9’5“.“ ...e .‘3‘

Figure 3.1. The quasi-isostatic technique used for determining MCP barrier
properties

 

 

'U
a:
ti
0)
E
8
O.
‘2’
'6 slope = Fss
c
E
3
9
Lag time (9) time

Figure 3.2. An example of typical amount of MCP vs. time plot from quasi-
isostatic permeability experiment

115

3.2.6 MCP controlled release devices

The monolithic device was a plastic sheet that had SmartFreshTM powder
dispersed in it. It was made by mixing approximately 180 mg of polymer matrix
with 30 mg of SmartFreshTM powder. This mixture was placed in a mold which
consisted of 3 metal sheets (Figure 3.3) stacked on top of each other. The
middle sheet had 22 mm circular openings into which the polymer matrix — active
compound mixture was placed. The two outer sheets were lined with thin
aluminum foil. The mold containing the mixture was compressed at a pressure
and temperature of 10,000 psi and 110°C for 5 minutes using a Carver laboratory
press (Model M, Carver, lnc., Wabash, IN). The mold was allowed to cool for 5
minutes to approximately 50°C before the pressure was released. The
monolithic device was made in the same manner in the absence of the

SmartFreshTM powder.

 

Figure 3.3. The mold used for processing of monolithic devices

116

The reservoir device was the two plastic sheets laminated together with
the SmartFreshTM powder in the middle. The two plastic sheets were made in the
same manner as the blank monolithic device. Approximately 30 mg of
SmartFreshTM were placed between the two sheets. The sheets were placed
between two metal sheets lined with aluminum foil and a pressure and
temperature of 2000 psi and 80°C for 50 seconds was applied using the Carver
laboratory press. The blank specimen for this device was made in the same
manner in the absence of the SmartFreshTM powder.

The monolithic and reservoir devices developed were formed in the shape
of a round disc with different thicknesses and diameter (Figure 3.4). Monolithic
LDPE and EVA devices had the same diameter of 22 mm and thickness of 550
:5 um. The reservoir device (LDPE membrane) diameter was 25 mm and its
thickness was 912:6 pm. The reservoir device (EVA membrane) diameter was
33 mm and its thickness was 624:6 um. The other difference in the reservoir
device was that the molecular encapsulation powder in the EVA device was
broken up into several small groups while the powder in the LDPE device was
continuous. The thickness across the surface was constant. This indicates that
the thickness of the LDPE and EVA membrane over the location of the powder
was less than 456 and 312 pm (half of the thickness of the reservoir device),

respectively.

117

Reservoir (EVA) Reservoir (LDPE) Monolithic (LDPE)

 

Figure 3.4. Monolithic and reservoir devices for MCP release study

3.2.7 Release of MCP

Release of MCP from the controlled release devices or the molecular
encapsulation complex was studied by subjecting them to a controlled
temperature and relative humidity (RH) in a 920 mL glass jar with a sampling port
(Figure 3.5). The controlled RH was achieved using a 100 mL saturated salt
solution or deionized water. The salt solution and the relative humidity are
shown in Table 3.1. The jar was placed in a controlled temperature chamber (5
or 22°C). A 250 uL aliquot was withdrawn from the glass jar and analyzed as
described in 3.2.4. The blank was also tested in the same manner as the
sample. The fraction of MCP released (Q) was calculated as:

volume of MCP released
expected volume of MCP to be released

 

Qt:

The expected MCP volume is the amount of MCP released at equilibrium (the

state where the volume of MCP in the headspace does not change with time)

118

from the molecular encapsulation complex subjected to the test temperature and

relative humidity.

Table 3.1. Salt solutions used in the study of MCP release and the expected
relative humidity they created at 4 and 22°C

 

 

 

Salt Solution % RH

4°C 22°C
Lithium chloride n/a 11
Magnesium chloride n/a 36
Magnesium nitrate n/a 53
Sodium Chloride nla 75
Ammonium sulfate 79 81
Potassium chloride 87 85
Potassium nitrate 97 93
Deionized water ~100 ~100

 

Sampling port

 

— Controlled released device

 

 

 

Salt solution

 

Figure 3.5. The setup of 920 mL glass jar containing salt solution or water
described in Table 3.1 used for the MCP release study.

119

The release profile is constructed by plotting the fraction of MCP released
or the volume or fraction of MCP released as a function of time. Each point on
the release profile is the average of 3 data points and the error bar represents a
standard error. The line graph on a release profile represents the predicted
fraction or volume of MCP released based on the empirical models (described in
Section 3.2.8).

3.2.8 The effect of MCP delivery devices on the MCP release
characteristics

The amount of MCP released from the monolithic devices (LDPE and EVA
matrices), reservoir devices (LDPE and EVA membranes), and the molecular
encapsulation complex was monitored at 22°C at a relative humidity of
approximately 100% by using water in place of a salt solution. The release
profiles were fitted with 3 empirical equations (Table 3.2). Q is fraction of MCP
released, t is time (day) and a and b are regression coefficients. The regression
analyses were performed using SigmaPlot 2000 (Version 6.10, Systat Software

Inc., Point Richmond, CA)

Table 3.2. Empirical equation used to describe the release profiles of MCP
delivery devices

 

 

 

Name Equation
Power function Q t = 34°
Modified hyperbola a-t
Qt =
1 + b . t
Exponential rise to maximum Qt = a-(1-e‘°‘)

 

120

All three functions, power, modified hyperbola and exponential rise to
maximum, had two regression coefficients. The coefficient a is a magnification
factor and increases when the Q at the equilibrium (constant MCP concentration
in the headspace) increases. The shape of the graph depends mainly on the
coefficient b. In the power function, for time less than 1 unit, the greater the b
value, the lower the release rate. For time greater than 1 unit, the release rate
increases with increase in b. One disadvantage of this equation is that it does
not approach a maximum level, thus, it is not suitable for describing a release
profile that includes the equilibrium portion (equilibrium state is defined as the
time that the concentration of MCP in the headspace is considered constant).
The modified hyperbola function is described by a first order reaction at the low t-
value and by a zero order reaction as the t-value increases (Al-Zahrani 2000).
As b increases, the change from the first to zero order release occurs at lower t
values and the change is more abrupt. When parameter a is constant, an
increasing b value indicates that the release rate and amount of MCP released
will decrease. In the exponential rise to maximum, an increasing b value

indicates a greater release rate.

3.2.9 The effect of temperatgre on t_he release of MCP

The amount of MCP released from the monolithic device (LDPE matrix),
reservoir device (LDPE membrane) and molecular encapsulation complex were
monitored at 5 and 22°C at approximately 100% RH by using deionized water.

The release profiles were fitted with 3 empirical equations as described in section

3.2.8.

121

3.2.10 ILe effect of relative humidity on the release of MCP

The amount of MCP released from the monolithic device, reservoir device
and molecular encapsulation complex was monitored at 5 and 22°C and various
RH (Table 3.3). The release profiles of the monolithic device were fitted with
modified hyperbola functions while the release profiles of the reservoir device
and the molecular encapsulation complex were fitted with an exponential rise to
maximum function. Since the expected volume was different for the different
relative humidities, both volume of MCP released and fraction of MCP released

were considered.

Table 3.3. Experiments performed to evaluate the effect of relative humidity on
the MCP release from the MCP delivery devices

 

 

Exp. Delivery device Polymer T, °C % RH
1 Monolithic LDPE 22 11, 36, 53, 75, 85, 93, ~100
2 Monolithic EVA 22 11, 36, 53, 75, ~100
3 Reservoir EVA 22 85, 93 and ~100
4 Molec. encapsulation - 22 11, 36, 53, 75, 81, 85, 95, ~100
5 Monolithic LDPE 5 87, 97 and ~100
6 Molec. encapsulation - 5 87, 97 and ~100

 

3.3 Results and Discussion

3.3.1 Therma_l analysis

Differential scanning calorimetry
The DSC thermogram (Figure 3.6) indicates that the theoretical onset

temperatures, according to ASTM D3418-03, were 103 and 84°C for LDPE and

122

EVA, respectively. Below this onset temperature, some melting had taken
places. The melting temperatures, which are the temperatures at the peak of
the DSC thermograms of LDPE and EVA, were 110 and 94°C, respectively.

These data can be useful to determine the minimum processing temperature for

controlled release devices.

 

T 103.19°C
. . l 120.5Jlg LDPE

l

 

 

 

 

 

.25
2 Z
.2 1
u. 1 1‘
‘4“: - 1‘ 0
f3 . , 83.62 C o
1 109.63 C
~ \ A, 80-3.0JI9 EVA
~ ~~~~~~~~~~~ *——/,+ ---------------------
...... r
x r
r
I
_ /
0
Exo up 94.44 C
U r Y 1 1 r T r Y Y Y I Y Y I I Y Y I l’ I T Y T Y 7 V
20 4 60 80 100 :20 140 :50
Temperature (C)

Figure 3.6. Differntial scanning calorimetric thermogram of low density
polyethylene (LDPE) and ethylene vinyl acetate (EVA) powder.

123

Thermal Gravimetn'c Analysis

The TGA thermogram (Figure 3.7) shows the weight change of the sample
as a function of temperature, which indicates the then'n'al stability of the sample.
The threshold for thermal degradation of LDPE and EVA powder occurred at
377°C and 319°C, respectively. Above these temperatures, the respective
polymers are expected to undergo thermal degradation. For the molecular
encapsulation complex, two weight loss events occurred at 209°C and 275°C.
The degradation temperature of or-cyclodextrin is in the range of 250-300°C
(Huang and others 1998). Degradation at 209°C is not in this range; therefore, it
is probably degradation of an additive in the SmartFreshT'“ product. Degradation
at 275°C is the degradation of cyclodextrin. The remaining mass of
approximately 20% (w/w) is a char that forms as a result of cyclodextrin
degradation (T rotta and others 2000).

The lower degradation temperature (200°C) is used to set the maximum
processing temperature for the controlled release devices. The processing
condition chosen was based on the DSC results for the polymer. It was set
below this temperature so it could safely be used for the MCP controlled release

device.

124

 

1001 “—1

Weight (%)

95

LDPE

376.96 C

 

 

 

100-
98*

96-

Weight (%)

94-

92

 

EVA

 

’ 319.17 C

 

 

100'“

80‘

Weight (%)

40‘

 

20

208.79 C

 

Active compound

275. 05 C

 

 

5'0' ' '100‘

-1510 ' ' 200 '
Temperature (C)

'250'

‘800'

to
Us .
c:

' 400

Figure 3.7. Thermogravimetric analysis thermogram for low density polyethylene
(LDPE), ethylene vinyl acetate (EVA) and the molecular encapsulation complex

125

3.3.2 Barrier properties

Moisture barrier
Water vapor permeability coefficients of LDPE and EVA at 10, 20 and
30°C and the activation energy of the permeation process are presented in Table

3.4. The Arrhenius plots of the two polymers are presented in Figure 3.8. The

Arrhenius equation for LDPE was:

k m 3.1 93.31838
m -s-Pa
The Arrhenius equation of EVA was:
k m £545.2ka
Pwater = 5.49x10'12 ____29 .e T
m -s-Pa

From the Arrhenius equation, the water vapor permeability coefficients of
the two polymers at 5 and 22°C were calculated (Table 3.5). Although 5°C is
outside the range of temperature used'in the determination of water vapor
barrier, the Arrhenius relationship was assumed to be valid because 5°C is well
above the glass transition temperature of both LDPE and EVA.

The water vapor diffusion (Dwater) and solubility (Swater) Coefficients were
not experimentally determined. A previous study has found that the water
diffusion coefficient of EVA was less than that of LDPE (Marias and others 1998;
Devallencourt and others 2002). Since the water vapor permeability coefficient
of EVA was much greater than that of LDPE, it can be deduced that water
solubility coefficient of EVA is substantially greater than that of LDPE.

126

Table 3.4. Water vapor permeability coefficient of low density polyethylene
(LDPE) and ethylene vinyl acetate (EVA) at 10, 20, and 30°C and activation
energy of the permeation process (Ep) at a relative humidity of approximately
90%

 

 

 

Polymer Pwater, x 1075 kg.m.m'2.s".Pa", Ep, kJ.mol'1
10°C 20°C 30°C
LDPE 2.45 i 0.05 2.93 i 0.04 4.03 i- 0.09 17.6 i 1.1
EVA 13.5 i: 0.2 18.6 i 0.1 23.4 :t 0.6 19.5 i 1.8

 

Note: The error term associated with the water vapor permeability coefficient is the standard error
(n=2) and the error term associated with the activation energy is the propagated error from the
standard error of the slope of the Arrhenius plot.

 

-33 4

 

lnP

-35 —I

 

 

 

-37 1
0.00325 0.00330 0.00335 0.00340 0.00345 0.00350 0.00355

 

1 I I I

1rr (1/K)

Figure 3.8. Arrhenius plot of water vapor permeability for low density
polyethylene (LDPE) and ethylene vinyl acetate (EVA) in the temperature range
of 10-30°C . The solid lines represent the predicted values and the dash lines
represent the confidence interval.

127

MCP barrier

The volume of MCP which permeated through the LDPE films for both test
temperatures are presented in Figure 3.9. The MCP permeability, diffusion and
solubility coefficients of LDPE at 5 and 22°C are presented in Table 3.6. All three
coefficients increased with increasing temperature. The permeability of MCP at
23°C was previously determined, also by a quasi-isostatic method (with slightly
different setup), by two other researchers to be 1.31 x 10'10 cc (at 23°C).m.m'2.s’
‘.Pa" (Lee 2003) and 1.77 x 101° cc (at 23°C).m.m'2.s".Pa" (Sittipod 2003).
Despite the similarity in the permeability coefficient, the diffusion and solubility
coefficients, determined in previous research (Lee 2003), were quite different
from the values obtained in this experiment. This may be due to a difference in
the base resin.

The MCP permeability of EVA could not be determined by the quasi-
isostatic method employed in this experiment because EVA absorbed MCP. A
significant decrease in MCP concentration in the high concentration side was
observed as the experiment proceeded. Thus, the MCP partial pressure
difference between the two sides of the film was not constant. This occurred
because EVA has a high MCP solubility coefficient. The solubility coefficient of
polymer containing vinyl acetate monomer was about 26 times higher than the
solubility coefficient of LDPE (Lee 2003). Lee also reported the MCP
permeability of EVA to be 1.56 x 101° cc (at 23°C).m.m°.s".Pa", which is very
similar to that of LDPE, and the diffusion coefficient to be 5.98 x 10'14 m2.s'1,

which is less than that of LDPE.

128

Table 3.5. Calculated water vapor permeability coefficient of low density
polyethylene (LDPE) and ethylene vinyl acetate (EVA) at 5 and 22°C

 

 

 

Polymer Calculated Pwater, x 1016 kg.m.m'§'1.Pa",
5°C 22°C
LDPE 2.09 3.24
EVA 1 1.8 19.7

 

Table 3.6. MCP permeability (PMCP), diffusion (DMCP) and solubility (SMCP)
coefficient of low density polyethylene at 5 and 22°C

 

 

Temperature, PMCP, DMcp, SMcp.
°C x 1010 cc.m.m'2.s".Pa'1 x 10’2.m2.s'1 cc.m'3.Pa'1
5 0.41 i 0.02 2.7 i- 0.16 15.4 i 1.5
22 2.1 i 0.18 5.7 i 0.27 37.5 i 2.0

 

Note: The error term is the standard error (n=3)

1.2

 

5°C

Volume of MCP, uL

 

 

 

 

Time, hr

Figure 3.9. The volume of MCP gas permeated through LDPE film during the
MCP barrier property testing at 4 and 22°C.

129

3.3.3 The effect of MCPeeliverv devices on the MCP release
Characteristgze

The fraction of MCP released (Q) of the controlled release devices,
monitored as a function of time, was fitted with three functions (listed in Table
3.2). All equations can be used to describe the release profiles with an adjusted
r2 in the range of 0.7 - 0.8 (Table 3.7). However, these functions are not suitable
to describe the fraction of MCP released from the molecular encapsulation
complex because some of the regression coefficients were not significant (Table
3.8). The reason was because the complex released MCP rapidly. The profile
was better described by two linear equations. The first equation described the
release during 0-3 hours where Q increased from 0 to 1 with the equation Q =
St. The second linear equation (Q = 1) described the fraction of MCP during
steady state. The experimental and the predicted values were used to construct
MCP release profiles (Figure 3.10 - 3.14). The functions that best described
each profile (the highest adjusted r2) were used to compare release of MCP from
each device (Figure 3.15).

The MCP delivery devices significantly affected the MCP release
characteristics. Enclosing the molecular encapsulation complex in polymer
matrix/membrane significantly reduced the MCP release rate (Figure 3.15). The
effect of polymer on the release rate has been shown in other applications with

fertilizers (Al-Zahrani 2000) and drugs (Burgos and others 2002).

130

Table 3.7. The regression coefficients and the adjusted r2 of the release profile
for MCP delivery devices for power, modified hyperbola and exponential rise to
maximum functions at 22°C and ~100% RH.

 

 

 

 

 

Model Regression Monolithic Reservoir
analysis LDPE EVA LDPE EVA
Power a 0.44 5. 0.08 0.39 i: 0.03 0.06 i 0.02 0.35 i 0.04
b 0.21 i 0.04 0.34 .1: 0.05 0.51 i 0.11 0.39 i 0.07
Adj. r2 0.7268 0.7476 0.8007 0.7284
Mod. a 2.02 i 0.05 1.15 i- 0.3 0.04 i 0.02 0.49 i 0.13
Hyperbola b 2.96 5: 0.83 1.64 5 0.49 0.10 i 007* 0.51 i 0.18
Adj. r2 0.7800 0.7709 0.7288 0.7786
Exp. rise a 0.62 i 0.03 0.61 i 0.04 0.34 i 0.10 0.80 i 0.60
to max. b 2.34 i 0.49 1.34 i 0.29 0.09 i 0.05+ 0.47 i 0.11
Adj. r2 0.7666 0.7616 0.7099 0.7906

 

I indicates that the regression coefficients was not significant

Table 3.8. The regression coefficients and the adjusted r2 of the MCP release
profile for the molecular encapsulated for power, modified hyperbola and
exponential rise to maximum functions at 5 and 22°C, ~100% RH.

 

 

 

 

 

Model Regression analysis Temperature
5°C 22°C
Power a 0.83 i 0.05 1.01 i 0.02
b 0.16 i 0.04 0.00 i 0.02"
Adj. r2 0.7125 0.9647
Mod. Hyperbola a 6.45 i 1.64 255824 i 70964101+
b 6.01 .+_ 1.71 255969 i 71032297+
Adj. r2 0.8326 0.9649
Exp. rise to max. a 1.01 :l: 0.04 1.00 i 0.02
b 3.98 i 0.67 2240 i 3635410“
Adj. r2 0.8746 0.9649

 

131

 

1.0-

 

Fraction of MCP released

 

 

 

 

14

Time (day)

Figure 3.10. The experimental release profiles of monolithic devices (LDPE
matrix) when subjected to 22°C and ~100% RH (circle) and the predicted
fraction of MCP released using the power function (solid line), the modified
hyperbola function (dotted line) and the exponential rise to maximum function
(dash-dotted line). The error bar represents standard error.

132

 

1.0 -

0.8 -

0.6 1

0.4 4

Fraction of MCP released

0.2 -

 

 

0.0

 

Time (day)

Figure 3.11. The experimental release profiles of monolithic devices (EVA
matrix) when subjected to 22°C and ~100% RH (circle) and the predicted
fraction of MCP released using the power function (solid line), the modified
hyperbola function (dotted line) and the exponential rise to maximum function
(dash-dotted line). The error bar represents standard error.

133

 

 

1.01
0.8— I I l

0.6 ~

Fraction of MCP released

 

 

 

 

 

25

Time (day)

Figure 3.12. The experimental release profiles of reservoir devices (LDPE
membrane) when subjected to 22°C and ~100% RH (circle for the intact devices
and triangle for the devices with compromised integrity) and the predicted
fraction of MCP released from the intact device using the power function (solid
line), the modified hyperbola function (dotted line) and the exponential rise to
maximum function (dash-dotted line). The error bar represents standard error.

134

 

 

 

 

 

1.0-
‘O
(D
g ’1’.
9 0.8- ,,__..- -~—-
9 ,/‘/
23 06 ‘/2 fl
2 ' 7 .
“6 /
8
'6: 0.4-1
f! .’
LL

0.2-1 4

0.0‘ I I r r I

0 2 4 6 8 10 12
Time(day)

Figure 3.13. The experimental release profiles of reservoir devices (EVA
membrane) when subjected to 22°C and ~100% RH (circle) and the predicted
fraction of fraction of MCP released using power function (solid line), modified
hyperbola function (dotted line) and exponential rise to maximum function (dash-
dotted line). The error bar represents standard error.

135

 

 

 

 

 

I 1- I

1.0 "‘ i T
e t
G)
8 J
2 0.8
9
8
2 0.6 1
“5
8
'3 0.4 '1
2
LI.

0.2 5

0.0 I I 7 I

-0.5 0.0 0.5 1.0 1.5 2.0 2.5

Time (day)

Figure 3.14. The experimental release profiles of molecular encapsulation
complex when subjected to 22°C and ~100% RH (circle) and the predicted
values of fraction of MCP released during equilibrium using a linear equation
(solid line). The error bar represents standard error.

136

 

1.04——

 

 

 

 

Fraction of MCP released

 

 

 

 

Time (day)

Figure 3.15. Comparison of predicted MCP delivery system: molecular
encapsulation complex (long dash), monolithic devices with LDPE matrix (solid
line) and EVA matrix (dotted line) and reservoir devices with LDPE membrane
(medium dash) and with EVA membrane (dash—dotted line).

137

The release in monolithic device depends on diffusion and, in some cases,
solution of active ingredient in the polymer (Zeoli and Kydonieus 1983). The
monolithic device in this study is slightly different because it involves the diffusion
and solution of triggering agent. The proposed model of MCP release from the
monolithic device in this study follows these steps:

1. Sorption of water into the surface of the polymer with subsequent diffusion
within the polymer matrix. Desorption from the polymer then occurs at the
interface of the matrix and the molecular encapsulation complex. The
interface can be anywhere in the polymer matrix.

2. Absorption of water molecules by the encapsulation complex.

3. Release of MCP from the encapsulation complex.

4. Sorption of MCP into the polymer at the matrix/encapsulation complex

. interface with subsequent diffusion within the polymer matrix and
desorption into the atmosphere in the release cell.

The release profiles of LDPE and EVA monolithic devices (Figure 3.15)
were best described by the modified hyperbola function. This equation was also
found to best describe the release profile of nitrogen phosphate and potash,
monoamonium phosphate, diammonim phosphate and granular
triplesuperphosphate fertilizer in polyethylene and paraffin wax matrices. (Al-
Zahrani 2000) The other two functions, experimental rise to maximum and
power function, can also be used to described the release profile with slightly
lower adjusted r2. All three functions showed that the LDPE matrix device had

higher regression coefficient b but only the modified hyperbola had a higher

138

coefficient a for the LDPE matrix device. This indicates that the LDPE device
released MCP faster than the EVA matrix device (based on all three functions)
but the release amount at equilibrium was similar (based on the power and
exponential rise to maximum functions). This was unexpected because EVA had
a greater permeability to both water vapor and MCP. The slower release rate
may be attributable to the fact that EVA absorbs MCP.

The proposed model for MCP release from the reservoir device is the
same as the model for the monolithic device except that the polymer/molecular
encapsulation complex interface is located between two polymer sheets.
Therefore, the water vapor and MCP molecules have to diffuse across the
thickness of the polymer sheet instead of some distance within the polymer.

The release profiles of LDPE reservoir devices were divided into two
groups according to their release rates (Figure 3.12). The first group included
those that released MCP very fast and the other group those that released only a
little MCP. After examining the devices, it was found that the two polymer sheets
in the first group could be easily peeled apart. This may have allowed the water
vapor and the released MCP to pass through some voids created by the
compromised integrity of the device. Therefore, only data from the second group
was used in determining the function that best described the MCP release profile.
MCP released from this device very slowly and did not reach equilibrium for more
than 20 days. This release profile was best described by the power function.

The EVA reservoir device released MCP at a much greater rate (Figure

3.13) than the LDPE reservoir device and released up to 80% of the expected

139

amount. This release profile was best described by the exponential rise to
maximum function. The release rate from the reservoir (EVA membrane) was
significantly greater than that of the LDPE membrane'device. The release rate of
the reservoir devices depends on permeation of both active compound and the
release triggering agent (water). Both water and MCP need to permeate across
the polymer sheet in order for the release to happen. The MCP permeability
coefficient for EVA was slightly greater than that of LDPE, according to Lee
(2003) by the factor of 1.2 times. The water vapor permeability coefficient of
LDPE was 16% of the water vapor permeability coefficient of EVA. Based on the
total thickness of the device, the thickness of LDPE can be at least 1.5 times
greater than the thickness of EVA membrane. With thickness correction, the
transmission rate of MCP and water vapor across LDPE was 57% and 11% of
the rates across EVA membrane. This indicates that both MCP and water vapor
transmission across polymer sheets had influence on the slower MCP release
from the LDPE device but water vapor permeability had greater impact.

Over time, the surface of the monolithic devices changed from smooth to
rough, while the surface of the EVA membrane reservoir device was smooth but
its thickness increased significantly in the presence of the molecular
encapsulation complex. Neither smoothness nor thickness changes were
detected in the reservoir (LDPE matrix), which only released a small amount of
MCP. The increase in the roughness of the monolithic device and the thickness

of the reservoir device (EVA membrane) was not a result of change in polymer

140

dimensions but a result of the moisture absorption by the molecular
encapsulation powder, which caused the powder to swell and then liquefy.

When LDPE reservoir and monolithic devices Containing LDPE were
compared, it was found that the monolithic device released more MCP and at a
higher rate. The rate limiting factor should be the amount of water that reached
the molecular encapsulation complex. In the monolithic devices, the
polymer/encapsulation complex interfaces are located throughout the polymer
and, thus, can start releasing MCP faster. In the reservoir device, it can take a
very long time for the molecular encapsulation to receive enough moisture to
cause the release of MCP due to the moisture barrier of the LDPE.

When the reservoir and monolithic devices containing EVA were
compared, the reservoir device released more MCP but at a slower rate than the
monolithic device. The greater release rate in the monolithic device can be
explained by the existence of the interface between the polymer and the
encapsulation complex like in the LDPE devices. The lower amount released
from the monolithic device may be attributable to absorption of MCP by EVA, as
observed in the MCP permeability experiment. The other possibility might be
that, the moisture absorption of molecular encapsulation complex in the
monolithic device located closer to the surface retarded the movement water
vapor to the inner part of the device and/or the movement of MCP from the inner

part of the device.

141

3.3.4 The effect of temperature on the release of MCP

The effect of temperature on the release rate was studied in the molecular
encapsulation complex and in the LDPE monolithic and reservoir devices at a
relative humidity of ~100%. The amount of MCP released from the molecular
encapsulation complex at 5 and 22°C was not significantly different (p-value =
0.10) (Figure 3.16) but the release rate was quite different. As explained in 3.3.4
the release rate of the molecular encapsulation complex at 22°C was very fast
and was described by two linear equations as described in 3.3.4. The fraction of
MCP released from the encapsulation complex at 5°C was slower and was well
described with the exponential rise to maximum function (Table 3.8). The
molecular encapsulation powder at both temperatures became liquefied at the
end of the evaluation period. The slower release rate could be due to the slower
water absorption rate at a low temperature condition.

Temperature had a significant effect on the release rate of monolithic
(LDPE matrix) devices. The device at both temperatures had a rough surface at _
the end of the release evaluation period. Figure 3.17 shows that the devices
held at 5°C released less MCP and at a slower rate. This was also shown in the
regression coefficients a and b for all 3 functions, power, modified hyperbola and
exponential rise to maximum (Table 3.9).

The release amount and the release rate of reservoir devices with the
LDPE membrane held at 5 and 22°C were very low (Figure 3.18) and no change
in either the thickness or surface was detected. The regression coefficients

(Table 3.9) suggested that none of the three functions can be used to describe

142

the release profile of the device at 5°C because the device released a very low

amount of MCP and reached equilibrium in a short time. The power function was

the only function of the three used that could describe the release profile of the

device at 22°C.

Higher temperature resulted in a higher release amount of MCP as well as

a higher release rate in both monolithic and reservoir. The greater release rate

was due to the enhanced MCP and water vapor permeation at higher

temperature and the greater water absorption rate of the molecular encapsulation

complex at higher temperature. The reduced amount of MCP released at lower

temperature may have been the result of reduced water vapor permeation rate;

Thus, less water vapor are available for the molecular encapsulation complex to

absorb. _

Table 3.9. The regression coefficients and the adjusted r2 of the release profile
for MCP controlled release devices for power, modified hyperbola and

exponential rise to maximum functions at 5 and 22°C, ~100% RH.

 

 

 

 

 

Model Regression Monolithic (LDPE) Reservoir (LDPE)
analysis 5°C 22°C 5°C 22°C
Power a 0.14 i 0.01 0.35 i 0.02 0.09 :t 0.02 0.06 i 0.02
b 0.22 i 0.03 0.19 i 0.02 0.13 i 0.08” 0.51 i 0.11
Adj. r2 0.8193 0.8678 0.1982 0.8007
Mod. a 0.40 i 0.07 1.27 d: 0.24 0.28 i 0.20“ 0.04 i 0.02
Hyperbola b 1.64 i 0.33 2.33 i 0.51 2.17 i 175* 0.10 e 0.07:
Adj. r2 0.8739 0.8439 0.2348 0.7288
Exp. rise a 0.22 i 0.01 0.50 i 0.02 0.12 i 0.01 0.34 i 0.10
to max. b 1.15 i 0.18 1.59 i 0.28 1.21 i 0.68+ 0.09 i 0.05+
Adj. r2 0.8558 0.7846 0.2348 0.7099

 

+ indicates that the regression coefficient was not significant

143

 

 

 

 

 

 

 

 

16 g 22°C
14 - “l ...... 3% .......................... § ..............
3 12 - . I 5°C
'0 x
8
3 1° ‘ <5
9 .-
5 8-
2 .-
‘5 6 - 5
d) f
g .
5 4 ‘
2 - 5
0 J) I I I I
o 1 2 3 4 5
Time (day)

Figure 3.16. Volume of MCP released from approximately 30 mg of the
molecular encapsulation complex at 5 and 22°C, ~100% RH. The error bar
represents standard error.

144

 

1.0 -

0.8 4

0.6 -1

 

0.4 ~

Fraction of MCP released

oz ~

 

 

0.0

 

 

16

Time (day)

Figure 3.17. The experimental MCP release profiles of monolithic devices at 5°C
(white circle) and at 22°C (black circle) and the predicted values of MCP release
using the modified hyperbola function at 5°C (dotted line) and 22°C (solid line).
The error bar represents standard error.

145

 

1.0 -

 

 

 

8
m 0.8 ~
(U
.9
9
0- _
O 0.6
2
“-
o
8 04 a
“3
g 22°C
u.
5°C
25

 

Time (day)

Figure 3.18. The experimental MCP release profiles of reservoir devices at 5°C
(white circle) and at 22°C (black circle) and the predicted values of MCP release

using the modified hyperbola function at 5°C (dotted line) and 22°C (solid line).
The error bar represents standard error.

146

3.3.5 The effect of relat_ive humidity on the reltejse of MCP at 22°C
The effect of relative humidity was studied on monolithic (LDPE and EVA

matrices) and reservoir (EVA membrane) devices and the molecular
encapsulation complex. The release profiles were then compared to the release
profile of the molecular encapsulation complex at the same temperature and
relative humidity, represented as the fraction of MCP released.
MCP molecular encapsulation complex

Relative humidity has a significant impact on the volume of MCP released
from the molecular encapsulation complex (Figure 3.19). The complex did not
release MCP when subjected to RH of 75% or less. MCP began to desorb at
81 % RH but the volume of MCP released was quite low. The powder was
completely liquefied only when subjected to 93 and 100% RH. At 81 and 85%,
the powder absorbed enough moisture to cause caking. No difference in
appearance of the powder was observed at the other relative humidity levels.

The effect of relative humidity (81 % to ~100%) was analyzed by fitting the
release profile (based on the volume of MCP released) with the exponential rise
to maximum function, which was previously found to best describe the release
profile. The regression coefficients (Table 3.10) indicate that when the relative
humidity increased, the amount of MCP released increased (higher coefficient a).
The release rates at 81 and 85% relative humidity, as indicated by parameter b,
were not significantly different but they were both less than at 93% RH. The

release rate at ~100% was the highest.

147

20

 

 

 

 

 

81% RH

34; 151 E i ~100% RH

'8 ill: f 93% RH
1 j i

9 10«

CL

0

2

“5 g2 Q

g 5_ :16 § 85% RH
% i
> i "f f

 

 

 

 

ii i
0_ E11, 36, 53, 75% RH

I

0 2 4

 

 

 

 

-

O)
C!)

Time (day)

Figure 3.19. The experimental data for MCP volume released from the molecular
encapsulation complex at 22°C when subjected to 11% RH (closed circle), 36%
RH (open circle), 53% RH (closed triangle), 75% RH (open triangle), 81% RH
(closed diamond), 85% RH (open diamond), 93% RH (closed square) and
~100% RH (open square). The predicted data based on linear function (11, 36,
53, 75 and ~100% RH) and exponential rise to maximum function (81, 85, 93%
RH) are presented as a solid line. The error bar represents standard error.

148

Table 3.10. The regression coefficients and the adjusted r2 of the volume of
MCP released from the molecular encapsulation complex for an exponential rise
to maximum function at 22°C.

 

 

 

Relative humidity MCP Volume released
a b Adj. r2
81% 2.94 i 0.22 3.34 _+_ 1.22 0.5764
85% 5.42 i 0.05 3.59 i 0.90 0.6723
93% 13.90 i 0.04 10.13 i 2.54 0.7756
~100% 14.39 i 0.27 2109 : 3635410+ 0.9649

 

" indicates that the regression coefficients was not significant

Monolithic device (EVA and LDPE matrices)

Relative humidity had a similar effect on the monolithic devices for both
EVA and LDPE matrices (Figure 3.20 and 3.21). No MCP was released when
either polymer matrix was subjected to a relative humidity of 75% or less.
Change in surface roughness of the device was found at 85% RH but to a much
lesser extent than at 93 and ~100% RH. The release profile at higher relative
humidity was described by the modified hyperbola function, which was found to
best describe the release profile of the monolithic device in a section 3.3.4. For
devices with an EVA matrix, the only relative humidity tested was at ~100%. At
this relative humidity, the device released MCP and the release profile based on
the volume and ratio of MCP released was described by the following equations:

(16.86 i 4.08)-t
1+(1.64.t0.50)-t

 

v,=

(1.15i0.27)-t
Qt
1+(1.64i0.49)-t

 

149

The adjusted r2 values for the Vt and Q. equations were 0.7631 and 0.7786,
respectively. All regression coefficients were significant. The fraction of MCP

released as a function of time was presented in Figure 3.11.

 

 

 

 

 

 

 

12
1o - ~100% RH
3 ' ' .
8 8 ~
(0
CD
2 I
9
a 5 ‘ .
0
2
”5 .
o ’4 'j '
E r
2 1'
§ 2 - :j 11, 36,53, 75% RH
O - "3": g g
o 2 4 6
Time (day)

Figure 3.20. The experimental data for MCP volume released from the
monolithic (EVA matrix) devices at 22°C when subjected to 11% RH (closed
circle), 36% RH (open circle), 53% RH (closed triangle), 75% RH (open triangle)
and ~100% RH (open square). The predicted data are based on linear function

(11, 36, 53, 75) and modified hyperbola (100% RH) and are presented as a solid
line. The error bar represents standard error.

150

14

 

 

 

 

 

 

 

 

 

 

12 ~ __
j l
3
8 1° . n ~100% RH
U) i I
8
'g 8 ‘ 1. . ..
CL ' 93% RH
I
‘3’ 6 - E 3F ,
*5 l!
(D
E 4 "l u i x 0
2 ~ ' 4—
g ' . . l 85% RH
2 ‘ 'i" ’ . <5
{1'95 . 11, 36, 53, 75% RH
o - ..;$-«—. '—————'
0 2 4 6 8 10 12 14 16
Time (day)

Figure 3.21. The experimental data for MCP volume released from the
monolithic devices (LDPE matrix) at 22°C when subjected to 11% RH (closed
circle), 36% RH (open circle), 53% RH (closed triangle), 75% RH (open triangle),
85% RH (open diamond), 93% RH (closed square) and ~100% RH (open
square). The predicted data based on a linear function (11, 36, 53 and 75% RH)
and modified hyperbola (85, 93 and 100% RH) are presented as a solid line. The
error bar represents standard error.

151

Table 3.11. The regression coefficients and the adjusted r2 of the MCP released
from the monolithic devices (LDPE matrix) for a modified hyperbola function at
22°C.

 

RH Volume of MCP released Ratio of MCP released

 

a b Adj. r2 a b Adj. r2

 

85% 1.45 i 0.29 0.36 i 0.1 0.808 0.26 i 0.05 0.35 i 0.10 0.8150
93% 8.50 i 1.46 1.35 i 0.27 0.8685 0.63 :t 0.11 1.34 i 0.27 0.8720
~100% 29.12 i 7.12 2.96 i 0.82 0.7848 2.02 i 0.50 2.96 i 0.83 0.7800

 

The relationship of the MCP released (based on the volume and fraction
of MCP released) as a function of time for LDPE matrix device was also
described by a modified hyperbola function (Table 3.11). Both regression
coefficient a and b increased significantly with an increasing relative humidity
(Table 3.11). The amount of MCP released was greater and the rate was higher
at a higher relative humidity. The release rate based on fraction of MCP (Figure
3.22) followed the same pattern as the release profile based on the volume of
MCP released. However, the device at 85% RH released a higher fraction of
MCP than the device at 93 and ~100% RH.

Reservoir devices (EVA membrane)

EVA membrane reservoir devices were studied at 85, 93 and ~100%.
These were the conditions that provided sufficient moisture to release MCP from
the molecular encapsulation complex and the monolithic devices. Change in
thickness at the location of the powder agglomeration was observed at 93 and

100% RH. The reservoir device released MCP under all three conditions. As

152

 

‘LO

 

 

 

 

 

 

(18 - "
'8 I ~100% RH
m U a
8 - T
To 0.6 - i " . __.._.—-—-—-
o. . ~85% RH
(2) I ‘ . O .
“6 0.4 ~ I
~ 0
.5 9/ § i 93/o RH
g .. f ‘
I: 0.2 - a: v
l
0.0 ~ u
0 2 4 6 8 10 12 14 16
Time (day)

Figure 3.22. The experimental data for fraction of MCP released from the
monolithic devices (LDPE matrix) at 22°C when subjected to 85% RH (open
diamond), 93% RH (closed square) and ~100% RH (open square). The
predicted data based on modified hyperbola are presented in a solid line. The
error bar represents standard error.

153

time progressed up to 8 days, the volume of MCP in the test container increased
but between 8 and 16 days, the volume of MCP in the test container decreased.
This decrease after 8 days was not observed for any devices containing LDPE
polymer. The reduction of the MCP concentration in the headspace of the test
container is attributed to MCP absorption by EVA, as observed in the
permeability experiment.

Only the release rate (both fraction and volume) up to 8 days was used to
determine the regression coefficients of the exponential rise to maximum
function. Table 3.12 shows that the regression coefficients for devices at 93 and
~100% RH were not significantly different. Coefficient a at these two RH levels
was greater than that of the device at 85% RH based on the volume of MCP
released and significantly less than that of the device at 85% RH based on
fraction of MCP released. Coefficient b at 85% RH was not significantly different
from that at ~100% RH but slightly less than that at 93% RH. This indicates that
RH affected the volume of MCP released but did not have as much effect on the
rate at which it was released. The effect of relative humidity on the volume of
MCP released diminished at RH greater than 93%.

The fraction of MCP released as a function of time (Figure 3.24) shows
that the devices at 93 and ~100% RH released approximately 80% of the
expected MCP at these relative humidity levels. At 85% RH, the fraction of MCP
released was higher than at other relative humidities and the value was greater
than 1. This was also found in the monolithic device (LDPE matrix) where the

fraction of MCP released at 85% was higher than at 93%. This may be a result

154

Table 3.12. The regression coefficients and the adjusted r2 of the MCP released
from the reservoir devices (EVA membrane) for an exponential rise to maximum
function at 22°C.

 

RH Volume of MCP released Ratio of MCP released

 

a b Adj. r2 A b Adj. :2

 

85% 8.30 i 1.48 0.24 i 0.08 0.8293 1.50 :l: 0.27 0.24 i 0.09 0.8189
93% 10.67 i 0.85 0.60 i 0.15 0.8474 0.78 i 0.06 0.62 i 0.16 0.8363
~100% 12.24 :1: 1.24 0.38 i 0.10 0.8222 0.88 i 0.09 0.38 :01 0.8218

 

 

 

 

16
14 .
~100% RH
12 . -
/ . T
10 ~ /‘ . j _ ~93% RH

 

/, ~85%§H

O)

1
\
‘ O

O
0

Volume of MCP released (uL)
on

 

 

 

4 ..., '4 ’x
' O
U
2 - ,2",
A" Q
0 -1 I1"
0 2 4 6 8 10 12 14 16

Time (day)

Figure 3.23. The experimental data for MCP volume released from the reservoir
devices (EVA membrane) at 22°C when subjected to 85% RH (open diamond),
93% RH (closed square) and ~100% RH (open square). The predicted data
based on a modified hyperbola are presented as a solid line. The error bar
represents standard error.

155

L8

 

 

 

 

 

 

16-
~85% RH
1.4 4
U
m a
(I)
(I)
.92
2
g % ~100% H
2 _ T .L
g i ~93% RH
.9
23
9
I‘- E
8 10 12 14 16

 

Time (day)

Figure 3.24. The experimental data for fraction of MCP released from the
reservoir devices (EVA membrane) at 22°C when subjected to 85% RH (open
diamond), 93% RH (closed square) and ~100% RH (open square). The
predicted data based on a modified hyperbola are presented as a solid line. The
error bar represents standard error.

156

of an underestimation of MCP released from the molecular encapsulation
complex at 85% RH, which was used as the expected volume when calculate Q
at 85% RH.

According to these results, EVA is not an appropriate polymer for use in
MCP controlled release devices because it absorbs MCP. Although LDPE has
higher MCP and water barrier, it is a better choice due to its low interaction with
MCP. The LDPE monolithic device released more MCP at a faster rate than the
reservoir device. Therefore, the release rate of the monolithic device (LDPE

matrix) was chosen to further study the effect of relative humidity at 5°C.

3.3.6 The effect of relative humidiy on the release of MCP at 5;C_

MCP molecular encapsulation

The release rate of the molecular encapsulation complex at 5°C was
studied at 79, 87, 97 and 100% RH. In this range, the relative humidity affected
the release amount and the rate of MCP released from the complex (Figure
3.25). The exponential rise to maximum function was used to describe the
release profile. The regression coefficients are presented in Table 3.13. This
model described the release at 87, 97 and 100% RH satisfactorily. At 79% RH,
the atmospheric moisture was not enough to release a significant amount of
MCP from the complex. Because the coefficient b of exponential rise to
maximum function at 79% RH was large but not significant, this function was
reduced to a linear function of Q = a, which is a linear function. Both regression

coefficients (a and b) at 87% RH were less than at 97 and ~100% RH. This

157

Table 3.13. The regression coefficients and the adjusted r2 of the MCP released
from the molecular encapsulation complex for an exponential rise to maximum

function at 5°C.

 

 

 

RH Volume of MCP released
a b Adj. r2
79% 1.07 i 0.15 9.43 i 8.93+ 0.2153
87% 10.12 i 0.34 1.88 i 0.26 0.9135
97% 13.08 i 0.45 4.69 i 0.78 0.8757
~100% 13.81 :t 0.49 3.98 i 0.67 0.8746

 

" indicates that the regression coefficients was not significant

 

 

 

 

 

 

 

 

 

18

16 -
A 14 :F ~100% RH
3 T E T
g 12 4 g fem RH
U)
m T 35 '
9 104
e i §87% RH
o. 8 q
0
2
“5 6 2
0
5 ..
§

2 1 ‘790/0 RH
i
o _ I
0 1 2 3 4 5 6
Time (day)

Figure 3.25. The experimental data for volume of MCP released from the
molecular encapsulation complex at 5°C when subjected to 79% RH (closed
diamond), 87% RH (open diamond), 97% RH (closed square) and ~100% RH
(open square). The predicted data based on an exponential rise to maximum
function are presented as a solid line.

158

indicates that at 87% RH, less MCP was released from the complex than at 97
and ~100% RH and at a slower rate.
Monolithic devices (LDPE matrix)

The release of MCP from the monolithic device (LDPE matrix) was studied
at 87, 97 and ~100% RH. The release profiles (Figure 3.26) were fitted with a
modified hyperbola function. The regression parameters are presented in Table
3.14. The volume of MCP released from the devices at 87 and 97% RH was
very low and could not be described satisfactorily by the modified hyperbola
function as indicated by the insignificance of coefficients a and b. The fraction of
MCP released and the release rate at 87 and 97% relative humidity were very
similar (Figure 3.27). At these relative humidity levels, the device only released
about 10% of the amount of MCP expected to be released while at ~100% RH,
about 20% was released. Although 87 and 97% RH provided sufficient moisture
to result in the release of MCP from the molecular encapsulation, the low water
vapor permeability at this temperature prevented sufficient water from
permeating into the polymer. Thus, not enough moisture was available to

release MCP from the molecular complex.

Table 3.14. The regression coefficients and the adjusted r2 of the MCP released
from the monolithic device (LDPE matrix) for an exponential rise to maximum
function at 22°C.

 

RH Volume of MCP released Ratio of MCP released

 

A b Adj. r2 a b Adj. r2

 

87% 2.80 i 3.98‘ 2.92 i 4.61" 0.0815 0.28 i 0.40" 2.91 i 4.65” 0.0623
97% 1.04 :l; 0.52+ 0.59 :l: 0.38" 0.1318 0.08 i: 0.04+ 0.56 i 0.14" 0.4953
~100% 5.52 i 1.03 1.64 i 0.35 0.8602 0.40 _+_ 0.07 1.64 i 0.33 0.8739

 

159

 

~100% RH

31 8% ' ' E 41I

 

 

 

Volume of MCP released (uL)

 

 

 

.. " E 97% RHE
1 - y . ,4 _ T ,
..I' T 87% RHf

if

14

0 _ ....n
0 2 4 6 8 10 12 14

Time (day)

Figure 3.26. The experimental data for volume of MCP released from the
monolithic device (LDPE matrix) at 5°C when subjected to 85%. RH (open
diamond), 93% RH (closed square) and 100% RH (open square). The predicted
data based on an exponential rise to maximum are presented as a solid line.

160

1.0

 

 

 

 

 

 

 

0.8 -

.0

(D

8

9 l

93 0.6

0.

o

2

“5 0.4 ~

8

'8 ~100% RH

(0

II 0.2 - 3 g i a

87 and 97% RH
1 1 J? E
o 2 4 6 8 1o 12 14
Time (day)

Figure 3.27. The experimental data for fraction of MCP released from the
monolithic device (LDPE matrix) at 5°C when subjected to 85% RH (open
diamond), 93% RH (closed square) and 100% RH (open square). The predicted
data based on an exponential rise to maximum are presented as a solid line.

161

Of the two rate controlling polymers evaluated, LDPE was the more
suitable for use in the controlled release device. The main reason was that it did
not interact with (absorb) MCP. Of the two devices (LDPE matrix) the monolithic
device had a more desirable release rate because the reservoir device only
released a small amount of MCP even at the highest temperature and relative
humidity tested. The monolithic device also has several advantages over the
reservoir device. To make this device is a simpler process and can be
accomplished in one continuous step in large scale production. The molecular
encapsulation complex is also contained within the polymer matrix and,
therefore, it is not likely to disintegrate and prematurely release MCP immediately
when exposed to humid air. It would also prevent contamination of the product
with the encapsulation powder if the device disintegrated.

The controlled release device could be used for MCP treatment for any
produce that can benefit from repeated or continuous treatments such as
tomatoes, apples and avocados. The device is not intended to replace a single
treatment at the time of harvest because the release rate would be too slow to
achieve the right MCP concentration. The anticipated use is as an additional
treatment to prevent produce from regaining its sensitivity to ethylene. The
controlled release device allows in-package treatment by including this device in
a sealed package. When designing the in-package treatment, serious
consideration must be given to the packaging material used. The packaging
materials must have the following properties

- Heat sealable to prevent MCP escaping through pores or channels

162

- High MCP barrier to reduce the loss of MCP through permeation
- High water vapor barrier to retain moisture from respiration of the produce
and to create an atmosphere with sufficient RH to cause release of MCP
- Oxygen and carbon dioxide permeability should be appropriate to create
an optimum modified atmosphere condition and not cause anaerobic
respiration
Once the packaging system is decided, the number of device can be determined
according to the amount of produce in the package and MCP transmission rate
across the packages. The MCP mass transfer occurring in the package is
envisioned in Figure 3.28. MCP released from the device could be absorbed by

the produce, remain in headspace or permeate out from the package.

1

 

MCP controlled
rel ease device

 

   

\2/

Arrow represent the MCP mass transfer activity

 

Produce

 

 

 

Figure 3.28. The envisioned MCP mass transfer activity in produce - package
system containing MCP controlled release devices

163

The model for the amount of MCP absorbed by produce, MCP in the package
headspace, and MCP permeated out from the package is proposed with the
following assumption:
1. The fraction of MCP absorbed by produce is not concentration dependent.
2. The permeability of packaging material is not concentration dependent.
3. The permeation process of MCP in packaging material is at steady-state.
4. The headspace in the package is constant.
Based on these assumptions, the numerical model for MCP mass distribution for

a certain period of time is proposed to be:

 

n-(vtn.1—vm) = [x-W-At]+[vmcp]+[E-A[VMCP- atmj-m]
8 VHS

where n is number of devices in the package, Vt is the volume of MCP released
from device at time t, x is fraction of MCP absorbed by produce (= volume of
MCP/weight of fruits), W is weight of fruit, At is tn+1 - tn, VMcp is volume of MCP in
the headspace, P is permeability of packaging material, I? is thickness of
packaging material, A is surface are of the package, VHS is headspace volume,

and Pam. is atmospheric pressure.

3.4 Summary and Conclusion
Four controlled release devices, monolithic (LDPE and EVA matrices) and
reservoir (LDPE and EVA membrane), were developed and their release rates

were determined. The two polymer matrices of monolithic devices had similar

164

release profiles but EVA was found to absorb MCP which caused a reduction in
MCP concentration. The reservoir device released MCP at a slower rate than did
the monolithic device. Release from reservoir device depends largely on the
polymer membrane. The LDPE device released MCP very slowly while EVA
released a greater amount of MCP at a higher rate.

The storage conditions, i.e. temperature and relative humidity, had a
significant effect on MCP release from the device. The amount of MCP released
and the release rate were greater at higher temperature because both MCP and
water vapor permeation processes are enhanced. Relative humidity had a great
effect on the release rate. The minimum relative humidity that triggered the
release of MCP from the molecular encapsulation complex was 81 % and 87%
RH at 22 and 5°C, respectively. The release rate and release volume increased
with increasing RH for the monolithic device (LDPE matrix) at 22°C but at 5°C the
device only released a significant amount of MCP at ~100% RH. For the EVA
reservoir device, the increased RH resulted in an increased volume of MCP
released but did not affect the release rate.

The LDPE monolithic device has the most desirable characteristics both in
that it does not react with MCP and will not cause a safety concern in case
device disintegrates. The anticipated use of the device is as an in-package
treatment as a supplement to the single application following harvest of the
produce. It would be ideal for produce such as tomatoes, apples and avocados

that benefit from repeated and/or continuous exposure to MCP.

165

 

 

CONCLUSION

The objectives of this research were to evaluate MCP-treated apples as a
potential raw material for fresh-cut apples and, second, to develop of a device to
enable continuous in-package application of MCP.

The combination of MCP treatment and CA storage resulted in intact
apples with more firmness than intact apples subjected to the individual
treatment. This resulted in apple slices with greater firmness. However, slices
from apples subjected to the combination treatment had high susceptibility to
enzymatic browning, and thus, had the most flesh discoloration. In addition, they
had different volatile profiles from slices. Apples from the combination treatment
are suitable as the raw material of fresh-cut apples only when the enzymatic
browning can be minimized by controlling external factors through use of higher
concentration of antibrowning agent, well controlled cold chain distribution and
reduced oxygen atmosphere. When the external factors can not be tightly
controlled, MCP treated apples or CA storage apples are the better choice as
raw materials. At 3 months storage of intact apples, MCP-treated apples were
better than CA storage apples because they had the greatest firmness while their
susceptibility to enzymatic browning and the volatiles production were similar to
apples in CA storage. At 9 months storage, MCP treatment was the most
suitable treatment although the slice firmness had declined significantly. The
firmness was still greater than the minimum threshold (53.4 N). MCP treated

apple slices produced more hexyl acetate and were less sensitive to enzymatic

166

browning than slices from other apples. At 5 and 7 months storage, CA storage
apple and MCP treated apple slices had similar quality.

Four controlled release devices, monolithic (LDPE and EVA matrices) and
reservoir (LDPE and EVA membrane) were developed. The release profiles for
the four devices were similar but the amount of MCP released and the release
rate. Among them, the LDPE monolithic device had the most desirable
characteristics in that it did not react with MCP and for safety reason in the case
where the device may disintegrate. The release characteristics of the LDPE
monolithic device depended largely on temperature and relative humidity. The
amount of MCP released and the release rate from the device increased with
increasing temperature. The effects of relative humidity at 22 and 5°C were
different. The amount of MCP released and the release rate increased with an
increasing RH at 22°C but had very little effect at 5°C. The anticipated use of
the device as an in-package treatment would likely be to supplement the single
application after harvest for produce such as tomatoes, apples, and avocados

that benefit from repeated or continuous treatment MCP treatment.

167

APPENDICES

168

 

 

APPENDIX A

SAS CODES FOR STATISTICAL ANALYSIS OF APPLES CONDITION AND
FRESH-CUT APPLES QUALITY

SAS code for two-way analysis of variance used for analyzing the effect of MCP
treatment and storage atmosphere on the quality of apples before fresh-cut apple
processing

*******it*****************************************

proc mixed data=Initialapple;

by month;

class storage MCP;

model a=storage MCP storage*MCP;
lsmeans storage*MCP/diff;

run;
/a is a response, storage is storage atmosphere,
MCP is MCP treatment/

*1:************************************************

SAS code for repeated measurement analysis for analyzing the effect of
postharvest condition on flesh color and texture of fresh-cut apples during 14
days storage

*******************~k******~k***************~k******

proc mixed data=freshcut color;

by time;

class Storage MCP NS day apple;

model a= StorageIMCPINS|day/ddfm=satterth;
repeated day/type=ar(1)
subject=apple(storage*MCP*NS*day);

lsmeans Storage*MCP*NS/diff;

run;

/a is a response, storage is storage atmosphere,
MCP is MCP treatment, NS is antibrowning agent,

day is storage time of fresh—cut apple/
irir********************~k**************~k****~k******

169

SAS code for repeated measurement analysis for analyzing the effect of
postharvest condition on individually selected volatile compound during 14 day
storage.

***********************~k****************************

proc mixed data=volatiles;

by time;

class Storage MCP day apple;

model EA: StorageIMCPIday/ddfm=satterth;

repeated day/type=ar(1) subject=apple(storage*day);
lsmeans Storage*MCP*day/diff;

MAKE 'diffs' OUT=diff;

MAKE 'lsmeans' OUT=means;

run;

/a is a response, storage is storage atmosphere,
MCP is MCP treatment, day is storage time of fresh—
cut apple/

***~k*~k*~k**********~k********************~k************

170

APPENDIX B

STATISTICAL ANALYSIS OF THE EFFECT OF POSTHARVEST
TREATMENTS ON THE SUBSEQUENT QUALITY OF FRES-CUT APPLES

B1 . The effect of postharvest treatment on the condition of intact apples
before processing

Table 81. p-value for main effect and interaction of storage condition (storage)

and MCP treatments (MCP) of IEC, °Brix, firmness, L*, a* and b* after 3, 5, 7 and
9 month storage

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Response Factor Storage time, month
3 5 7 9
Ln (IEC) Storage 0.0070 <0.0001 <0.0001 <0.0001
MCP <0.0001 <0.0001 <0.0001 ns
Storage * MCP ns ns ns ns
°Brix Storage ns 0.0098 ns 0.0239
MCP ns ns < 0.0001 ns
Storage * MCP 0.0397 ns ns ns
Firmness Storage 0.0017 0.0001 0.0211 0.0010
MCP < 0.0001 0.0001 0.0002 0.0004
Storage * MCP 0.0125 ns ns ns
L* Storage ns 0.0099 0.0150 ns
MCP 0.0080 0.0132 0.0001 ns
Storage * MCP ns ns ns ns
3* Storage ns ns ns 0.0208
MCP ns ns ns ns
Storage * MCP ns ns ns ns
b* Storage ns ns ns ns
MCP ns ns ns 0.0208
Storage * MCP ns ns ns 0.0295

 

 

 

 

 

 

ns = not significant different (p-value > 0.05)

171

 

Table B2. Pairwise comparison of Ln (IEC) between 4 postharvest treatments at
3. 5, 7 and 9 month storage

months Air
+

 

denotes the

Table B3. Pairwise comparison of °Brix between 4 postharvest treatments at 3,
5, 7 and 9 month storage

Air Air + MCP CA CA + MCP
Air
Air + *
CA +
Air +

+

Air
+

 

172

Table B4. Pairwise comparison of firmness between 4 postharvest treatments at
3, 5, 7 and 9 month storage

time Air Air + MCP CA CA + MCP

3 months Air

Air + MCP *

CA *

CA + MCP *
5 months Air

Air + MCP

CA

CA + MCP
7 months Air

Air + MCP

CA

CA + MCP

Air

Air + MCP *

CA *

CA + MCP * * *
* denotes the statistically significant difference (p-value < 0.05)

 

Table B5. Pain/vise comparison of L*-value between 4 postharvest treatments at
3, 5, 7 and 9 month storage

time Air Air + MCP CA CA + MCP
3 months Air
Air + MCP *
CA
CA + MCP
5 months Air
Air + MCP
CA
CA + MCP
7 months Air
Air + MCP
CA
CA + MCP
9 months Air
Air + MCP
CA
CA + MCP

* denotes the statistically significant difference (p-value < 0.05)

 

173

Table BS. Pairwise comparison of a*-value between 4 postharvest treatments at
3, 5, 7 and 9 month storage

Air Air +

months

7 months

        

  

* denotes the significant (p—value <

Table B7. Pain/vise comparison of b*-value between 4 postharvest treatments at
3, 5, 7 and 9 month storage

Air +
Air
+
CA
+
Air
+

+

7 months

 

denotes the

174

82. The effect of postharvest treatment on the flesh color of FC apples

Table B8. p-value for main effect and interaction of storage condition (storage)
and MCP treatments (MCP), antibrowning treatment (AB) and shelf life (time) of
L*, a*, b* and AE of FC apples from apples after 3, 5, 7 and 9 month storage

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Response Factor Storage time of intact apples, month
3 5 7 9

L*-value Storag <0.0001 0.0001 <0.0001 <0.0001
MCP <0.0001 0.0001 <0.0001 <0.0001
Storage * MCP ns 0.0116 ns -
AB <0.0001 <0.0001 <0.0001 <0.0001
Storage * AB ns ns ns <0.0001
MCP * AB ns ns <0.0001 <0.0001
Storage * MCP * AB ns 0.0417 0.0023 -
Time <0.0001 <0.0001 <0.0001 <0.0001
Storage* time ns <0.0001 <0.0001 <0.0001
MCP * time ns ns ns ns
Storage * MCP * time ns ns ns -
AB * time ns ns ns <0.0001
Storage * AB * time ns ns ns ns
MCP * AB * time ns ns ns ns
Storage * MCP * AB *time ns ns ns ns

a*-value Storgge ns <0.0001 0.0109 ns
MCP 0.0065 0.0102 0.0002 ns
Storage * MCP ns <0.0001 ns -
AB <0.0001 <0.0001 <0.0001 <0.0001
Storage * AB ns ns ns 0.0017
MCP * AB ns ns 0.0035
Storage * MCP * AB ns 0.0079 ns -
Time <0.0001 <0.0001 <0.0001 <0.0001
Storage * time ns ns <0.0001 <0.0001
MCP * time ns ns ns ns
Storage * MCP * time ns ns ns ns
AB * time ns ns ns ns
Storage * AB * time ns ns ns ns
MCP * AB * time ns ns ns ns
Storage * MCP * AB *time ns ns ns ns

 

 

 

 

 

 

175

 

Table B8 (continued)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Response Factor Storage time of intact apples, month
3 5 7 9

b*-value Storage ns 0.0291 0.0395 <0.0001
MCP 0.0490 0.0020 0.0207 0.0130
Storage * MCP 0.0054 <0.0001 <0.0001 -
AB <0.0001 <0.0001 <0.0001 <0.0001
Storage * AB ns ns ns <0.0001
MCP * AB 0.1092 0.0022 0.0005 0.0008
Storage * MCP * AB ns 0.0152 0.0025 -
Time <0.0001 <0.0001 <0.0001 <0.0001
Storage * time ns ns ns 0.0002
MCP * time ns ns ns ns
Storage * MCP * time ns ns ns -
AB * time ns ns ns <0.0001
Storage * AB * time ns ns ns ns
MCP * AB * time ns ns ns ns
Storage * MCP * AB *time ns ns ns -

AE Storage ns <0.0001 <0.0001 <0.0001
MCP 0.0418 ns 0.0156 0.0130
Stogge * MCP ns 0.0092 ns -
AB <0.0001 <0.0001 <0.0001 <0.0001
Storage * AB ns ns ns <0.0001
MCP * AB ns ns 0.0053 0.0008
Storage * MCP * AB ns ns ns -
Time <0.0001 <0.0001 <0.0001 <0.0001
Storage * time ns ns <0.0001 0.0002
MCP * time ns ns ns ns
Storage * MCP * time ns ns ns -
AB * time ns ns ns <0.0001
Storage * AB * time ns ns ns ns
MCP * AB * time ns ns ns ns
Storage * MCP * AB *time ns ns ns -

 

 

 

 

 

 

ns = not significant different (p-value > 0.05)

176

 

Table 39. Pain~ise comparison of L*-value between 4 postharvest treatments A
(air), AM (Air + MCP), CA (controlled atmosphere storage) and CAM (CA + MCP)
with and without antibrowning agent (AB) at 3, 5, 7 and 9 month storage

Storage A AIAB AM AM/AB CA CA/AB CAM CAM/AB
time
3 mo. A
AIAB
AM
AM/AB
CA
CA/AB
CAM
CAM/AB
A ,
AIAB
AM
AM/AB
CA
CA/AB
CAM
CAM/AB
A
A/AB
AM
AM/AB
CA
CA/AB
CAM
CAM/AB
A
AIAB
AM
AM/AB
CA
CA/AB *
CAM * * *
CAM/AB - - * * *

* denotes the statistically significant difference (p-value < 0.05)

 

177

Table B10. Pairwise comparison of a*-value between 4 postharvest treatments A
(air), AM (Air + MCP), CA (controlled atmosphere storage) and CAM (CA + MCP)
with and without antibrowning agent (AB) at 3, 5, 7 and 9 month storage

Storage A AIAB AM AMIAB CA CA/AB CAM CAM/AB
time
3 mo. A
AIAB
AM
AMIAB
CA
CA/AB
CAM
CAM/AB
A
AIAB
AM
AMIAB
CA
CA/AB
CAM
CAM/AB
A
AIAB
AM
AMIAB
CA
CA/AB
CAM
CAM/AB
A
AIAB
AM
AMIAB
CA
CA/AB *
CAM *
CAM/AB *

* denotes the statistically significant difference (p—value < 0.05)

 

178

Table B11. Pairwise comparison of b*-value between 4 postharvest treatments A
(air), AM (Air + MCP), CA (controlled atmosphere storage) and CAM (CA + MCP)
with and without antibrowning agent (AB) at 3, 5, 7 and 9 month storage

Storage A AIAB AM AMIAB CA CA/AB CAM CAM/AB
time
3 mo. A

A/AB

AM

AMIAB

CA

CA/AB

CAM

CAM/AB

A

AIAB

AM

AM/AB

CA

CA/AB

CAM

CAM/AB

A

AIAB

AM

AM/AB

CA

CA/AB

CAM

CAM/AB

A

AIAB

AM

AMIAB

CA

CA/AB *

CAM *

CAM/AB * *
* denotes the statistically significant difference (p-value < 0.05)

 

179

Table B12. Pairwise comparison of AE between 4 postharvest treatments A (air),
AM (Air + MCP), CA (controlled atmosphere storage) and CAM (CA + MCP) with
and without antibrowning agent (AB) at 3, 5, 7 and 9 month storage

Storage A NAB AM AMIAB CA CA/AB CAM CAM/AB

time

3 mo. A
A/AB
AM
AMIAB
CA
CA/AB
CAM
CAM/AB
A
AIAB
AM
AMIAB
CA
CA/AB
CAM
CAM/AB
A
AIAB
AM
AMIAB
CA
CA/AB
CAM
CAM/AB
A
A/AB
AM
AMIAB
CA
CA/AB
CAM
CAM/AB - -

* denotes the statistically significant difference (p-value < 0.05)

 

180

B3. The effect of postharvest treatment on the texture of FC apples

Table B13. p-value for main effect and interaction of storage condition (storage)
and MCP treatments (MCP), antibrowning treatment (AB) and shelf life (time) of
texture of FC apples from apples after 3, 5, 7 and 9 month storage

 

 

 

Factor Storage time of intact apples, month

3 5 7 9
Storage <0.0001 <0.0001 <0.0001 <0.0001
MCP <0.0001 <0.0001 <0.0001 <0.0001
Storage * MCP ns ns 0.0108 -
AB 0.0178 0.0015 0.0118 <0.0001
Storage * AB ns ns ns ns
MCP * AB ns ns ns ns
Storage * MCP * AB ns ns ns -
Time ns ns ns ns
Storage * time ns ns ns ns
MCP * time ns ns ns ns
Storage * MCP * time ns ns ns -
AB * time ns ns ns ns
Storage * AB * time ns ns ns ns
MCP * AB * time ns ns ns ns
Storage * MCP * AB *time ns ns ns -

 

ns = not significant different (p-value > 0.05)

181

Table B14. Pairwise comparison of texture between 4 postharvest treatments A
(air), AM (Air + MCP), CA (controlled atmosphere storage) and CAM (CA + MCP)
with and without antibrowning agent (AB) at 3, 5, 7 and 9 month storage

Storage A AIAB AM AMIAB CA CA/AB CAM CAM/AB

time

3 mo. A
AIAB
AM
AM/AB
CA
CA/AB
CAM
CAM/AB
A
AIAB
AM
AMIAB
CA
CA/AB
CAM
CAM/AB
A
AIAB
AM
AMIAB
CA
CA/AB
CAM
CAM/AB
A
A/AB
AM
AMIAB
CA
CA/AB
CAM
CAM/AB - -

* denotes the statistically significant difference (p-value < 0.05)

 

182

 

B4. The effect of postharvest treatment on the hexyl acetate concentration
of FC apples

Table B15. p-value for main effect and interaction of storage condition (storage)
and MCP treatments (MCP) and shelf life (time) of hexyl acetate area response
apples from apples after 3, 5, 7 and 9 month storage

 

 

 

Factor Storage—time of intact apples, month

3 5 7 9
Storage 0.0020 ns 0.0001 0.0001
MCP <0.0001 ns ns ns
Storage * MCP 0.0039 0.0089 ns ns
Time 0.0027 ns ns ns
Storage * time 0.0030 ns ns ns
MCP * time 0.0053 ns ns ns
Storage * MCP * time 0.0060 ns ns ns

 

ns = not significant different (p-value > 0.05)

183

 

 

Table B16. Pairwise comparison of hexyl acetate concentration in the package
headspace of FC apples at the shelf life of 0, 1 and 2 weeks from intact apples
that received 4 postharvest treatments A (air), AM (Air + MCP), CA (controlled
atmosphere storage) and CAM (CA + MCP) at 3, 5, 7 and 9 month storage

Storage A0 A1 A2 AMO AM1 AM2 CAO CA1 CA2 CAMO CAM1 CAM2
time

3 mo.

A0

A1

A2
AMO
AM1
AM2
CAO
CA1
CA2
CAM1
CAM2
CAM3
A0

A1

A2
AMO
AM1
AM2
CAO
CA1
CA2
CAM1
CAM2

 

* denotes the statistically significant difference (p-value < 0.05)

184

APPENDIX C

MCP CALIBRATION CURVE

Since the known concentration of MCP gas was not available, 1-butadiene
was selected for construction of MCP calibration curve due to their similarity in
their chemical structure. 1-Butadiene was injected into a glass jar with a known
volume to give a concentration of 1.5, 6, 33.3 and 100 uL L'1 in the headspace.
The volume of 50, 100, 200, 300, 400 and 500 uL of the headspace were
withdrawn using the airtight syringe and injected into a gas chromatography
equipped with a flame ionization detector. The calibration curve is presented in
Figure C1. The statistical analysis were presented in Table C1-C2.

MCP calibration curve prepared using 1-Butadiene isa linear relationship
in the range of 0 - 0.06 pl of MCP. The calibration equation is:

Area response = (6012408 * volume of 1-butadiene) + 3575.01
This equation is adequately describe the relationship of the area response from
gas chromatography and volume of 1-butadiene injected (p-value < 0.0001).
Both the slope and the intercept of the models are significant (both p-values <
0.0001). The intercept represents the area response when injected blank (air
without 1-butadiene). Thus, when use the calibration equation to calculate the
concentration of MCP, the area response of the blank for that particular day was
subtracted from the area response of the sample. Then, only the slope was used

to calculate the concentration as in the following equation:

185

Corrected area response
6012408

volume of MCP =

 

3.5e+5

 

3.0e+5 ~

2.5e+5 4

2.0e+5 .

1.5e+5 ~

Area response

1.0e+5 ~

5.0e+4 4

 

 

 

 

0.0 1 1

I I

0.00 0.01 0.02 0.03 0.04 0.05 0.06

volume of MCP, uL

Figure 00.1. MCP calibration curve prepared using 1-butadiene. The solid line
represents the predicted value and the dotted lines represent the prediction
interval.

Table C1. Analysis of variance for calibration equation

 

df SS MS F Significance F

 

Regression 1 4.44E+1 1 4.44E+1 1 27054.53 8.53E-86
Residual 64 1.05E+09 16413459

 

Total 65 4.45E+1 1

Table CZ. t-test results for regression parameters of calibration equation

 

 

Coefficients Standard Error t Stat P-value
Intercept 3575.01 610.292 5.86 1.77E-07
Slope 6012408 36553.45 164.48 8.53E-86

 

186

APPENDIX D

CALCULATION OF THE REQUIRED AMOUNT OF SMARTFRESHTM

Example of the calculation of the amount of SmartFreshTM required to established

a desired concentration of MCP (X uL.L") in a treatment chamber with volume =

V liter.

1) Volume of MCP in a treatment chamber = VMcp (mL) = x.v x 10'3
2) Weight of MCP in a treatment chamber, w (9) is calculated based on the
Ideal gas Law.

p.V = L31
MW

Where P is pressure (atm)
MW is molecular weight of MCP (54 g)
R is gas constant (82.06 atm.mL.mo|e".K")
T is temperature (K)

100-w

3) Amount Of SmartFresh” required = % active ingredient of SmartFresh

 

To determine the amount of SmartFreshTM required to established 1 pL L'1 of

MCP in 30 gallon (113.56 L) barrel, used in Chapter 2, are shown as an example.

Volume of MCP in a treatment chamber = VMcp = 1 x 113.56 x 10'3 mL

187

Weight of MCP in a treatment chamber, w (9) is calculated based on the

Ideal gas Law.

1 atm X11356 x10"3 mL = l - 82.06m - (273 + 20)
54 9 mole K
w = 0.00026 9
Amount of SmartFreshTM required = 100x0.00026g = 0.18 g

 

0.14

188

 

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