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This is to certify that the
thesis entitled
Modified—atmosphere packaging of apple slices: Modeling
respiration and package oxygen partial pressures as a
function of temperature and film characteristics

presented by

RUOMWADEE LAKAKUL

has been accepted towards fulfillment
of the requirements for

Master .degree in Eackagm‘ g.

 

v
Major professor

Date Nov 15, 1994.

0-7639 MS U is an AflirmaliveAction/Equal Opportunity Inxtitution

 

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DATE DUE DATE DUE DATE DUE
JAN—G—Q—ZUQ
14 .L a 1i

MSUIeAn.““ ‘L ... -j m" 4 ',' "u.

 

MODIFIED-ATMOSPHERE PACKAGING OF APPLE SLICES: MODELING
RESPIRATION AND PACKAGE OXYGEN PARTIAL PRESSURE AS FUNCTION
OF TEMPERATURE AND FILM CHARACTERISTICS
By

Ruomwadee Lakakul

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

School Of Packaging

1994

 

ABSTRACT
MODIFIED-ATMOSPHERE PACKAGING OF APPLE SLICES: MODELING
RESPIRATION AND PACKAGE OXYGEN PARTIAL PRESSURES AS A
FUNCTION OF TEMPERATURE AND FILM CHARACTERISTICS.
By

Ruomwadee Lakakul

A systematic approach was taken to acquire information for the design of a modified-
atmosphere packaging (MAP) system for apple slices. Initially, various combinations
of O2 and CO2 were assessed for their control of tissue browning, thereby generating
target gas concentrations for package design. Reduced O2 and elevated CO2
atmospheres were applied to sliced apples and while some gas concentrations
significantly reduced browning relative to air controls, none of the treatments
prevented browning to a sufficient level to be acceptable. MAP was used as a tool
for obtaining respiratory data needed to calculated permeability characteristics of
packaging films that will obtain and achieve and maintain desired gas levels in the
package headspace at O, 5, 10 and 15C. The lowest 02 patial pressure to which fruit
could be exposed without fermentation increased with increasing temperature. A
mathematical model was developed to characterize the relationship between steady-
state 02 partial pressure (p.02) and 02 uptake and film permeability to 02 of packages.
The p92 model was used for predicting the effect of P02, activation energy (Epo’),

temperature, film type, and film thickness on p92,

 

"And whatever you do, whether in work or deed,
do it all in the name of the Lord Jesus,
giving thanks to God the Father through him."
Colossians 3:17.

iii

 

ACKNOWLEDGEMENTS

I would like to thank Dr. Ruben Hernandez for advice, help, and support.
Special thank for Dr. Randolph M. Beaudry for his patient training, support and
understanding through out this project.

Give thanks to:

Dr. Bruce Harte, Dr. Art Cameron , Chowdary Talasila

My family: Mom Dad and Poom

My family: Pee Ro, Pee Lau, and Nong Pha

Hospitality of people in the Hort. Lab: Rufino, Weimin, Yali, Cathy,

Phillipos, and Others

Friends: Fon, Duke, Ru, Pang, Pee Kok, and others

iv

 

Guidance Committee:

The journal paper format was chosen for this thesis in accordance with
departmental and university regulations. The thesis is divided into 2 chapters in
which Chapter II has been prepared according to format requirements for Journal of

the American Society for Horticultural Science.

 

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FIGURES

LIST OF SYMBOLS

INTRODUCTION

REFERENCES

CHAPTER I

1. Literature Review: Browning in apple and modeling of MAP
2.

References

CHAPTERII

Modified-atmosphere packaging of apple slices: Modeling respiration

and package oxygen partial pressure of temperature
and film characteristics

O\UI&UJNv—s

. Abstract

. Introduction

. Materials and Methods
. Results

. Discussion

. References

5

vi

Page

VIII-ix
x-xiii
xiv-xvi
1-2

3

4-23
24-29

3 1

32-34
35-41
41-48
48-55
56-58

 

TABLE OF CONTENTS (cont.)

Page
CHAPTER III CONCLUSION 115-116
CHAPTER IV APPEDICES
1. Appendix A 117-119
2. Appendix B 120-121

3. Appendix C 122

vii

 

LIST OF TABLES

Results
Table Page

1. Weight of fruit (g), thickness (mils), and surface area of pouches (cm?) were
used to generated range of 02 partial pressure inside the packages at 0, 5, 10,
and 15C, calculated from equation 3. 59

2. Effect of 02, C02, and time on ‘L’, ‘a’, and ‘b’ values of Slice apple tissue of
cultivar ‘Ida Red’ held at 5C. The values of ‘L’, ‘a’, and ‘b’ immediately
after cutting were 84.98, 2.55, and 14.90, respectively. 60

3. Effect of C02 concentration on C02 concentration on CO2 injury of apple
slices rating from 1-4 scale (1 =none, 2=slight, 3=moderate, and 4=severe)
on cultivar ‘Ida Red’ held at 5C. ‘ 61

4. Lower 02 limit for apple slices held at O, 5, 10, and 15C. The O2 partial
pressure inside the package were estimated from the curve describing the
relationship between RQ and 02 partial pressure (Figure 12) 02 partial
pressure below which a sharp increase of RQ took place. 62

5. Values for a, b, c, m, and n in equations 12 and 13 describing the relationship
between 02 uptake and 02 partial pressure inside the package were fitted
Simultaneously for O, 5, 10, and 15C and standard error calculated by using
SAS. ' 63

6. V,m and KT for 0, 5, 10, and 15C calculated from the fitted model;

V,m = O.602e°""”’T - 0.377 mmol-kg‘1-h’1
and KT = 0.05T + 0.662 kPa. 64

viii

 

LIST OF TABLES (cont.)

Appendix A Page
Table

1. Analysis of variance procedure for ‘L’, ‘a’, and ‘b’ values 117
2. Analysis of variance procedure; effects of each treatment and between

treatments to ‘L’, ‘a’, and ‘b’ values. 118

Analysis of variance procedure for CO2 injury 119

ix

 

LIST OF FIGURES

Chapter I
Illustration Page
1. Enzymatic browning reaction, Showing site of action of reducing agents which

include such browning inhibitors as sulfiting agents and ascorbic acid. 7
Chapter H

Figure

1. Effect of time on the ‘L’, ‘a’, and ‘b’ values of Sliced apple tissue of
cultivar ‘Ida Red’ at 0C (closed circle) and cultivar ‘NY674’ at room
temperature (23C) (open circle). Data were fitted with exponential equation
y =ae‘”‘+c. 65

2. Effect of time and temperature on the ‘L’ value of sliced apple tissue of
the cultivar ‘Ida Red’ in air. Data were fitted with exponential equation
y =ae‘”‘+c. 67

3. Effect of time and temperature on the ‘a’ value of sliced apple tissue of
the cultivar ‘Ida Red’ in air. Data were fitted with exponential equation
y =ae‘”‘+c. 69

4. Effect of time and temperature on the ‘b’ value of sliced apple tissue of
the cultivar ‘Ida Red’ in air. Data were fitted with exponential equation
y=ae""+c. 71

5. The time (Tm) required for ‘L’, ‘a’ and ‘b’ values to reach half way
between initial and final value of sliced apple tissue of cultivar ‘Ida Red’
in air from using the best fit curves of Figures 2, 3, and 4. 73

10.

11.

12.

13.

LIST OF FIGURES (cont.)

Page

Effect of temperature on film permeability to O2 and C02 for 3 mi] and 4 mil
(0.00762 cm and 0.01016 cm) LDPE films used in packaging experiments.
Bars represent i std, n =3. 75

Arrhenius plot of 02 and C02 permeability for 3 and 4 mil LDPE film used in
packaging experiments with r2 = 0.99. 77

Effect of temperature on relative rate for rates of reaction possesing range

Of activation energies including those of the P02 of some films (Saran, PVC,
PP, and LDPE). Data were generated using the Arrhenius equation (equation
5) and before transformed to a relative rate of l at 0C. 79

Effects of steady state 02 partial pressure and storage temperatures on
the rate of 02 uptake of apple slices cultivar ‘NY674’ in sealed LDPE
packages. 81

Composite curves demonstrating the effects of steady-state 02 partial
pressure and storage temperatures (0, 5, 10, and 15C) on the rate of
02 uptake of apple slices cultivar ‘NY 674’ in sealed LDPE packages. 83

Effect of steady state 02 partial pressure and storage temperatures
on the C02 production of apple slices cultivar ‘N Y674’ in sealed LDPE
packages. 85

Effect of steady-state 02 partial pressure on the respiratory quotient
of apple slices in sealed LDPE packages held at 0, 5, 10, and 15C. 87

Relationship between headspace ethanol vapor partial pressure and the
respiratory quotient of apple slices in LDPE sealed packages at four
temperatures. 89

xi

 

15.

16.

17.

18.

19.

20.

21.

LIST OF FIGURES (cont.)

Page

Effect of steady state 02 partial pressure and storage temperatuer on the

rate of 02 uptake of apple slices cultivar ‘NY674’ in sealed LDPE packages.
Curves are depict the best-fit respiratory model for 0, 5, 10, and 15C
(equation 14). 91

Effect of temperature on for Vum as determined from respiratory model with
values for a, b, and c as given in Table 5. 93

Effect of temperature on for KT as determined from respiratory model with
values for m and n as given in Table 5. 95

Effect of temperature on the rate of 02 uptake over a range of O2 partial
pressure for apple slices. Data were obtained from the fitted 02 partial
pressure model (equation 14). 97

Effect of temperature and O2 partial pressure on Qlo (the rate of 02 uptake
at temperature T+ 10C divided by rate of 02 uptake at temperature TC) of
apple Slices in the sealed LDPE packages. Data were Obtained from the fitted
02 partial pressure model. 99

Predicted 02 partial pressure changes in MA packages of sliced apple based
on initial optimization to 0.6 kPa at 0C for films with various values for
activation energy. Predicted ()2 partial pressure inside the package were
generated using Equation 18 with appropriate substitutions from Equation 14.
Film permeability was assumed to respond temperature as in Figure 8. 101

Predicted 02 partial pressure changes in MA packages of sliced apple based

on initial optimization to 1.2 kPa at 15C for films with different values for
activation energy. Predicted 02 partial pressure were generated using Equation
18 with appropriate substitutions from equation 14. Film permeability was
assumed to respond temperature as in Figure 8. 103

xii

 

22.

23.

24.

25.

LIST OF FIGURES (cont.)

Page

Effect of temperature on predicted 02 partial pressure for packages of apple
Slices composed of LDPE having a range of thicknesses. Predictions were
generated using equation 18 with appropriate substitutions from equation 18.
3- fold lower 02 limit dash line was represents an exponential equation Lower
02 limit = 0. 587*e 00‘" fitted to lower 02 estimates (Table 4).105

Effect of temperature on predicted O2 partial pressure for packages of apple
slices composed of LDPE, posessing various ratios of Wl/A of LDPE
packages of apple slices. Predictions were generated using equation 18 with
appropriate substitutions from equation 14. 3-fold lower 02 limit dash line
represents by an exponential equation Lower 02 limit = 0.587"‘e°'0m fitted to
lower 02 estimates (Table 4). 107

Validation of the model by designing packages target headspace 02 from
3.575E-07 and 2E-07 Wl/A ratios in Figure 23. 3-fold lower 02 limit dash
line represents by an exponential equation Lower 02 1imit= O. 587* ° 0‘"
fitted to lower 02 estimates (Table 4). 109

Effect of ranges of thicknesses of various films on 02 partial pressure in the
package at 0C. Thicknesses noted will provide aerobic conditions throughout
the temperature range shown. Curves were generated from the fitted 0202
partial pressure model (Equation 18) with substitution of different Epoz.

Lines parallel x-axis represent the range of thickness of each film that can

be used in aerobic range. 111

Appendix B

1.

Calculated apparent activation energy (EaR° 2) for sliced apple fruit respirationR
as affected by temperature and 02 partial pressure. Calculated values for Ba °2
obtained by stepwise numerical integration of the relationship between ln(02
uptake) and 1/Temperature In K at 02 partial pressure 0.3, 0.5, 1, 4, and 16
kPa. 120

xiii

 

Q10

LIST OF SYMBOLS

Parameters

Surface area of polymer, cm2

Activation energy of 02 uptake by fruit, kJ°mol°l
Activation energy of polymer O2 permeation, kJ - mol'1
Total 02 flux into the package, mmol - h" (Fick’s law)
02 partial pressure at half-maximal 02 uptake, kPa
Thickness of polymer, cm

Permeability constant

02 Permeability coefficient, mmol-cm1-cm'2-h'1-kPa‘l
C02 Permeability coefficient, mmol-cm‘-cm'2-h"-kPa'1
02 partial pressure inside the package, kPa

CO2 partail pressure inside the package, kPa

O2 partial pressure outside the package, kPa
C02 partial pressure outside the package, kPa

R02 at (T+10)/R(,2 at T

xiv

 

E<1 '-l 53% f 75

2

LIST OF SYMBOLS (cont.)

The gas constant 0.0083144 kJ-mol'1 K’1

02 uptake of fruit per unit weight, mmol'kg‘l h’1
Total 02 uptake of packaged fruit, mmol'h‘l
Temperature in celsius or kelvin

Maximum R02 as a function Of T, mmol'kg'l'h‘l

Weight of packaged fruit, kg

XV

   

INTRODUCTION

Lightly processed vegetables which include lettuce, cabbage, broccoli,
cauliflower, etc. , have found widespread acceptance and have been readily
incorporated into food service offerings. Fruit products, such as apple slices, have I
potential for successful entry into a precut fruit market. The purpose of this research
was to determine necessary packaging characteristics (e. g. package dimensions, film
permeability to 02 and C02, temperature sensitivity of 02 and C02 permeability, etc)
to generate acceptable atmospheres within packages for Sliced apple fruit. The first
goal was to determine target 02 and C02 to control the browning reaction of sliced
fruit. The second goal was to collect respiratory data for the development of a
respiratory model for sliced apple such that package characteristics needed to achieve
and maintain target gas concentrations could be identified. To this end, the model
was used to predict the Steady-state package oxygen partial pressure as a function of
temperature and film permeability.

Apple Slices undergo rapid tissue browning. Atmosphere with reduced 02 or
elevated CO, concentrations have been commonly used to reduce apple respiration and
extend storage life. In addition, certain proportions of these gases have also been

found to reduce browning reaction in some commodities. Controlled-atmosphere

 

2

technique was used to target 02 and CO2 concentration for controlling browning
reaction in apple Slices.

For model development, the respiration of apple slices described by 02 uptake
as function of temperature and package 02 partial pressure was defined using a
package approach. A respiratory model was developed by empirically fitting the data
with Michaelis-Menten type model (Lee et al., 1991; Cameron et al., 1994) or
Langmuir’s equation (Hemadez and Gavara, 1994). Maximal 02 uptake and the
package 02 partial pressure at half maximum 02 have temperature sensitivity and can
be defined by the model. The package 02 model can be developed from respiratory
model related with permeability characteristics according to Fick’s law. The 02
partial pressure inside the package can be predicted according to the model as a

function Of temperature and permeability characteristics.

 

REFERENCES

Cameron, A.C., R.M. Beaudry, N.H. Banks, and M.V. Yelanich. 1994. Modified-
atmosphere packaging of blueberry fruit: modeling respiration and package

oxygen partial pressures as a function of temperature. J. Amer. Soc. Hort.
Sci. 119(3):534-539.

Hernandez R.J. and R. Gavara. 1994. Sorption and transport of water in nylon-6
films. J. of Polymer Sci: part B: Polymer Physics vol 32:2367-2374.

Lee, D.S., P.E. Haggar, J. Lee, and KL Yam. 1991. Model for fresh produce
reparation in modified atmospheres based on principles of enzyme kinetics. J.
Food Sci. 56(6):1580—1585.

 

CHAPTER I

LITERATURE REVIEW

Browning in apples and modeling of Modified-atmosphere packaging

 

5
Lightly processed produce, also known as precut, value-added, fresh-processed

or fresh-cut produce, are packaged produce items that comprise the most rapidly
growing segment of the fresh produce industry. In January, 1994 issue of the trade
journal, Packer reported that within the $57 billion/year produce industry in 1992,
lightly processed products comprised approximately $2 billion. Retail sales of fresh-
cuts, or lightly processed produce, an unknown category a few years ago, commanded
a 6% of retail produce sales nationally, and up to 11% in California. Recent sales
figures indicate sales of refrigerated prepared salads and coleslaw increased almost
93% from 1992 to 1993 (anonymous, 1994). The primary driving force behind their
use is the convenience offered to food service industry and consumers. Consumers
(retail and institutional users) have demonstrated that they are willing to pay
substantially more for ready-to-use lightly processed produce than whole produce.
Lightly processed vegetables which include among other lettuce, cabbage,
broccoli, and cauliflower have found widespread acceptance or readily incorporated
into food service offerings. On the other hand, lightly processed fruit products,
unlike their vegetable counterparts, have been Slower to develop. Sliced fruits with
higher sugar and water contents which contributes to significantly problems with
moisture loss, decay and tissue softening. Another important impediment to a lightly
processed fruit product is rapid tissue browning. New technology to protect
processed lightly processed fruits from physical and physiological damage are being
developed. Once these processing methods are developed, significant market outlets

should soon open for fruit, especially since lightly processed vegetables are so widely

6

accepted. Perhaps the most likely and successful lightly processed fruit product is

apple slices.

1. Browning in cut apples

As indicated above, browning Of the cut tissue of apple slices is a major
quality concern. Enzymatic browning develops easily in cut fruits such as apples,
pears, peaches, bananas, and grapes, and vegetables such as potatoes, mushrooms and
lettuce. Coloration reactions can occur after bruising or cutting and they affect
significantly the produce shelf-life.

The browning process constitutes a complex set of reactions between the
product tissue and environment factors. To a large extent, browning in apples
involves the oxidation by polyphenol oxidase (PPO). Its substrates include phenols
such as caffeic acid derivatives, chlorogenic acid, (+)—catechin, and (-)-epicatechin
(Nadudvari-Markus and Vamos-Vigyazo, 1984), and atmospheric oxygen. In the
browning reaction, monophenolic compounds are hydroxylated to o-diphenols, and
these latter are oxidized to o-quinones (Mayer and Hare], 1979; Vamos-Vigyyazo,
1981; McEvily et al., 1992). On the other hand, o-quinones are highly reactive
compounds and can polymerize spontaneously to form high-molecular-weight
compounds such as the brown pigment melanin, or react with amino acids and
proteins (non-enzymatic reaction) that enhances the brown color produced (McEvily et
al., 1992). A variety of phenolic compounds are oxidized by PPO; the most common

substrates are catechins, cinnamic acid esters, 3,4—hydroxyphenyl-alanin (DOPA), and

7
tyrosine (Sapers G.M., 1993). PPO takes the name of tyrosinase, o-diphenol oxidase,

catechol oxidase, etc. , depending upon the substrate. In apple peel (Red delicious),
4-methyl catechol, chlorogenic acid, catechol and catechin are substrates of PPO

(Vamos-Vigyyazo, 1981).

 

 

 

 

OH OH O C 1
amp e:
O M CE “M £1 —- ....
R R OH R O ”We"
Monophenol O-Dihydroxy phenol O-Quinone Amino Acids
Proteins
1 J Phenolic Compounds
Quinons
Reducing Agent

Illustration 1: Enzymatic browning reaction, showing site of action of reducing agents

which include such browning inhibitors as sulfiting agents and ascorbic acid.

The severity of enzymatic browning on cut surfaces of apple slices will depend
partly on the extent of the damage done to surface tissues by the peeling or cutting
procedure. A water-jet cutting system was found to produce more subsurface cellular
damage in sliced potato than a sharp stainless steel knife blade, as judged by scanning
electron microscopic observation and measurement of protein extractability at the cut
surface (Backer and Gray, 1992).

The degree of browning is also dependent on the amount and activity of PPO
and substrate. Cultivars of apples differ in their tendency to brown due to variation
in PPO activity and substrate content. For instance, NY 674 apples are lower in
polyphenol oxidase and polyphenols content compared to other cultivars (Lee and

McLellan, 1990). The cut surface of N Y674 tissue showed least low degree change

 

8

of browning change in ’L’ values among 12 cultivars tested (Kim et a1, 1993). Such
differences can be used in the selection of cultivars that give the condition to
minimize browning.

Senescent browning (SB); a common feature of product deterioration, can be
prevented or reduced by using C02 enriched atmosphere. The brown pigments of
senescent browning are generated by the oxidation of phenolic compounds by PPO.
These phenolic compounds come from the hydroxylation of cinnamic acid which is
formed by the deamination of phenylalanine catalyzed by phenylalanine ammonia-
lyase (PAL) (Mateos, 1993). Under environmental with high concentration of C02,
PAL activity is induced whereas phenolic production and browning is inhibited.
Control of low degree of browning is lost when lettuce tissue is transferred from C02
to air which cause rapid increase in soluble phenolic content (Siriphanich and Kader,
1985). Elevated value of CO2 concentration can reduce browning of mechanically
damaged green beans by inhibiting formation of phenolic compounds and phenolase

activity (Buesher and Henderson, 1977).

H. Browning Inhibition
A.) Controlled Atmosphere storage

As browning is the product of complex oxidative reactions and therefore a
direct function of oxygen concentration, it can be retarded by the decreasing O2 in
direct contract with the cut surface of the fruit. Atmospheres with reduced 02 and/or

elevated CO; concentrations have been commonly used to reduce apple respiration and

 

9

extend storage life. Studies have shown that there are optimal values of 02/C02 rater
in preventing browning (Rolle and Chism, 1987). For example, elevated CO2 levels
delay brown discoloration of lettuce (Siriphanich and Kader, 1985).

However, minimum percentage of (1-3%) 02 is necessary for maintenance of
aerobic respiration. Usually 02 concentrations of less than 1% create anaerobic
conditions for the living cells, whereby energy requirements of tissues are supplied
via glycolysis and fermentation rather than through the TCA cycle. The by—products
of fermentation include ethanol and acetaldehyde, which can contribute to off flavor
development (Rolle and Chism, 1987).

Although the use of elevated C02 treatments has been shown to have desirable
effects, controlling the environment, influencing respiration and controlling browning
for some commodities, negative effects may occurs if concentrations exceed certain
critical levels. High values of CO2 concentrations decrease energy supplied to tissues
by inhibiting various respiratory enzymes (Shipway and Bramlage, 1973). Where cut
apples are treated with high CO2 concentration, areas around the core are injured
producing a dry and brown surface. C02 treatments can also induce the development
Of off—flavors and cause physical damage if the level is too high.

Barrett (1989) found that apples stored under typical CA conditions; 1-3% 02
and 3-5% C02, and analyzed immediately did not havea trace of brown discoloration
in their tissues. On the other hand, the cortical tissue of apples stored under varying
CO; conditions (8%, 9%, 10% and 12%) was observed to be both browner initially

and to darken: faster after 30 minutes in air than apples stored under typical CA

10

conditions. This finding agrees with the results of Liu and Pan (1989) who found that
’Delicious’ apples stored under the same varying high C02 conditions had
Significantly greater flesh browning than normal CA stored apples after 6 months.

Since 02 is required for enzymatic browning, reducing oxygen from contact
with product can delay the reaction. MAP has the potential to be used to control gas
concentrations in the package. However, excessive reduction of oxygen must be
avoided to prevent anaerobic conditions that can damage the tissue by inducing
anaerobic metabolism, leading to tissue breakdown and off-flavor formation. Further
more, anaerobic condition in the package are also favorable for the growth of

Clostridium botulinum, very dangerous microorganism.

B.) Chemical treatment

A number of chemical treatments exist that are able to control browning.
These treatment are commonly based of sulfiting agents. Sulfur dioxide, sodium
sulfite, potassium bisulfite and potassium metabisulfites are highly effective in
controlling not only both enzymatic and non-enzymatic browning but also the growth
of microorganisms (Sapers, 1993). However, sulfites are subject to regulatory
restrictions by the FDA because of adverse effects on human health. FDA
restrictions on the use of sulfites in certain fruit and vegetable products have
prompted researchers to develop sulfite substitutes. Ascorbic acid (vitamin C) is
probably the best known alternative to sulfite. It reduces quinones back to phenolic

compounds before they can undergo further reaction to form pigments. Ascorbic acid

 

11

and its isomer erythorbic (d—isoascorbic) acid have been used to inhibit enzymatic
browning in fresh-cut apples. As reported by El-shimi, 1993; Tressler and Dubois,
1944, these two compound can be added to syrups solution, sometimes in combination
with citric acid and calcium salt, for dipping of the fruits.

Sulfites inhibitors present greater chemical stability and better penetration than
ascorbic acid-based inhibitors, for these reasons the latter are less effective. To
improve the performance of the ascorbic acid more stable derivatives have developed.
Stable formulations include, ascorbic acid-2-phosphates, ascorbyl palmitate and other
fatty acid esters of ascorbic acid, a-glucosyl ascorbic acid. The rate of penetration
can be increased by treating the fruit under pressure or vacuum instead of dipping or
spraying (Sapers et al., 1990).

The use of PFC inhibitors such as cinnamic acid and benzoic acid in
combination with ascorbic acid (Sapers et al. , 1989), carbon monoxide and kojic acid
[5-hydroxy-2-(hydroxymethyl)- -pyrone] (Chen et al., 1991) has been reported.
Dudley and Hotchkiss ( 1989) reported that cysteine prevents brown pigment formation
by reacting with quinone intermediates to form stable, colorless compounds. Molnar-
Perl and Friedman (1990) suggested that reduced glutathione and N-acetylcysteine are
nearly as effective as sulfites in controlling browning in apple, potato, and fresh fruit
juices. Bromelain, an enzyme present in pineapples, proved to be effective for
inhibiting browning in refrigerated apple slices (Lozano-de-Gonzalez et al., 1993).
Further studies by Lozano-De-Gonzalez (1993) has confirmed that pineapple juice and

ion exchanged pineapple juice (pineapple juice where organic acids and amino acids

l2

and small peptides were removed) are a good alternatives to sulfites for preventing
browning in fresh and dried apple products.

Interestingly, honey has been shown to inhibit enzymatic browning on white
grapes and cut fruits. Indeed, honey found effective in retarding flesh color change
of MA packaged apple Slices (Lee et al., 1994). This effect appears to be associated
more with the presence in honey of a small peptide weight of about 600 Datton than

to the reduction of dissolved oxygen due to the sucrose (Oszmianski and Lee, 1990).

C.) Edible coating

An edible coating was reported to prevent enzymatic browning of mushroom
slices (Nisperos-Carriedo et al.,l99l) and sliced apples. The USDA researcher Attila
Pavlath has developed a FDA approved, tasteless seaweed-based gel coating that can
prevent browning for fourteen days on apple slices (personal communication).
Pavlath has also created a spray formulated with the calcium salt of vitamin C which
can be found in many green vegetables. It can keep a cut apple fresh for two or three
days. John Krochat, a researcher at the University of California Davis, is attempting
to develop a transparent coating derived from components of milk on sliced apples
(Krochat, personal communication). A cellulose-based coating, called ‘Nature seal’ ,
now has been used for carrots, papaya, and pears by acquired by EcoScience of

Worcester, Mass. (Stephens, 1994).

 

13

III. Decay Concern

Physiological decay, in addition to browning, is still a major obstacle
remaining to the commercial production of sliced apple and other fruit. Two
diseases, the blue mould rot and grey mould rot in apples which are caused by
Penicillium expansum Link and Botrytis cinerea Pers. respectively, commonly affect
stored apples (Snowdon, 1990). These microorganisms penetrate wounded tissue
causing physiological damages and decay development. So it seems plausible that
they may be responsible for the decay in sliced apples too. Possibly there are other
species that can grow in the surface of Slice apple. The control of these species is
achieved by a combination of chemical and physical methods. Chemical control
methods, (pre- and post-harvest), are directed at eliminating, or substantially
reducing, the primary inoculum input into stores and in certain crops. Chemical
control can be accomplished by washing and applying fungicide in sprays, aqueous
washes, as dusts, or by fumigation. Physical control methods often affect the activity
of both host and pathogen and include atmosphere modification, low and high
temperature, heat treatment and irradiation, and are generally intended to retard the
onset of decay in storage (Maude, 1980).

Modified-atmospheres have been found to effectively retard the growth of
some microorganisms. High carbon dioxide (10-20%) or low oxygen (1-0.25%)
reduced decay of strawberries caused by B. cinerea (Couey and Wells, 1970). Carbon
dioxide storage was preferred by Couey and Wells (1970) because insufficient oxygen

results in anaerobic respiration leading to ‘invasive alcohol poisoning’ or off-flavors.

14

Fungi, in general, are more sensitive to elevated carbon dioxide than to low oxygen.
However, injuries caused by carbon dioxide limit the level of C02 that can be used.

Decay ‘control can also be achieved through the application of chemical food
additives such as 802, irradiation or fungicide. However, the use of this type of
additives poses health hazards to human consumption such as in the case of the
allergic response to sulfites. For these reasons, the use Of ‘natural’ preservative
compounds and techniques has a greater appeal to most consumers. At present, no
chemical materials are applied to lightly processed products.

There have been investigations into the possibility of using biological control
of the fruit decay. Janisiewicz (personal communication) has described a pink yeast,
Sporobolomyces roseus-occurring naturally on the surface of pears, that reduces blue
mold on apples up to 100% and gray mold up to nearly 80%. Furthermore, by
adding a sugar (2-deoxy-d-glucose) to the antagonistic yeast Candida saitoana, Wilson
and E1 Ghaouth (personal communication) have discovered a new biocontrol agent to
protect peaches and apples from postharvest rots of apples treated with this yeast-
sugar combination, 80% completely resisted the Botrytis cinerea rot pathogen after 16
days. Ecogen (Langhorne, PA) & Ecoscience (Falmoth, MA) companies are now
commercially making a new biocontrol agent.

Decay control using volatile antifungal compounds holds some promise as an
alternative to materials and techniques discussed so far. This technology ‘fits well’
with packaging applications where the volatile material can be incorporated in the

packaging material for treating the commodity right at the time of consumption.

15

Antifungal volatile materials such as benzaldehyde, 1-hexanol, E—2-hexanal and 2-
nonanone, released by red raspberries and strawberries during ripening can control
decay in package fruit (Vaughn et al. 1993). Among those compounds, 2-nonanone
has surfaced as a likely candidate due to its relatively low toxicity to the fruit, very
low mammalian toxicity, a pleasant fruity odor and commercial availability. 2-
nonanone is also a generally recognized as safe (GRAS) compound and is listed for
food application under Synthetic Flavoring Substance and Adjuvants (FDA, 172.515).
Levels of volatile compounds other than 02, CO2 and H20 can accurately be
modeled based on their production rate within the package (Beaudry et al.,1993).
The implication is that the steady-state approach can be used for manipulating
headspace concentration of a number of volatiles, including that may have antifungal
properties. Maintenance of continuous volatile concentrations will probably be
necessary due to the fact that most volatiles are fungistatic rather than fungicidal.
Advances in controlled-releases/delivery technology for volatile materials such as
pheromone suggest that a continuous release system can be developed for packages.
Prior to this advance, a model is need to predict the necessary film characteristics to
maintain acceptable levels of Oz and C02 inside the package as a function of oxygen

partial pressure.

III. Modified Atmosphere Packaging (MAP)
MAP is a process to extend the shelf-life of fresh fruits and vegetables.

Target gas compositions surrounding a product is dependent upon the product’s

l6

requirements, gas exchange and sensitivity of desirable physiological processes to gas
levels. Most fresh fruits and vegetables can be stored longer in low 02 and high CO2
atmosphere than in air (Kader, 1989). For apple slices, MAP can possibly be used to
facilitate the use of volatile antifungal compounds, maintain aerobic conditions and
maintain sterile conditions.

Modification of the internal atmosphere is attained through respiration of the
product within the sealed package and depends on the interaction of respiratory
characteristics of the product and the permeability properties of packaging film. The
natural process of respiration of products is used to reduce 02 and increase C02 under
restricted gas exchange through a barrier. Permeable films are usually used and
available as a barrier to create modified atmosphere (Talasila et al. , 1992). The
reduction in 02 concentration and increase in C02 concentration create gradients
causing O2 to enter and CO2 to exit the package. When 02 consumption equals 02
diffusion into the package and C02 production equals C02 diffusion out of the
package, steady-state conditions are achieved (Kader,1989).

One approach for designing an MA package that generates a physiologically
effective package 02 partial pressure is to match the total respiratory 02 uptake of the
packaged product with the total 02 permeation through the film according to the

following equation (Kader,1989; Beaudry et al., 1992; Cameron et al., 1994):

P A
W = 02 [p002 _ p302] (1)

R5?“ = R02 1

 

17

Where R: is total 02 uptake of package fruit (mmol-h“), R02 is 02 uptake of fruit per
unit weight (mmol-kg‘1-h"), P02 is 02 permeability coefficient (mmol-cm‘-cm'2-h“°kPa'
1), p.02 is 02 partial pressure of inside the package (kPa), W is fruit weight (kg), A
surface area of the package (cm2) and l is the thickness of the film (cm).

As can be seen from the equation 1, the total 02 uptake by the product is a
function of the fruit weight, surface area, thickness of the film and type of film that
will be used (permeability coefficient). If the 02 level inside the package falls below
that supporting aerobic respiration, anaerobic condition or fermentation may occur.
Although the tissue can tolerate anaerobic conditions, extended exposure to these
conditions leads to browning, off-flavors and loss of economic value. MA packages
should be designed to maintain safe and effective partial pressures of 02 and C02 over
a wide range of temperatures (e. g. 0 to 30C) because there is a risk of temperature
abuse during shipping, handling, and marketing. Therefore, the need for an accurate
determination of the lower 02 limit is required for MAP. Gran and Beaudry (1993)
described a method for determining the lower 02 limit as defined by the 02 level at
the upswing in the respiratory quotient (RQ) or RQ breakpoint, as 02 levels become
limiting to aerobic respiration.

Selection of a film that will result in a favorable atmosphere should be based
on the expected respiration rate at the transit and Storage temperature and the known
optimum 02 and C02 concentrations. The 02 level in the package should be higher

than lower 02 limit and C02 level should be lower than harmful C02 levels. A

18

suitable film requires much more permeability to CO2 than 02. Fortunately, most
commercially available films are about 4 to 5 times more permeable to C02 than 02.
In addition to differential Oz and CO2 permeabilities, some desirable
characteristics of plastic films for MAP of fresh produce include having required
permeabilities for the different gases, good transparency and gloss, low weight, high
tear strength and elongation, low temperature heat-scalability, lack of toxicity,
nonreactivty with produce, good thermal and ozone resistance, good weatherability,
commercial snitability and, ease of handling, printing and labeling (Kader, 1989).
There are few kinds of polymers routinely used for packaging fresh produce
such as PVC, polystyrene, polyethylene, and polypropylene. Polyolefins;
polyethylene, polypropylene, and polybutylene as well as their copolymers, are
typified by their good water vapor barrier properties, their relatively high gas
permeabilities, and their favorable response to heat sealing. Among those, LDPE
(specific gravity = 0.910 to 0.925) has high ratio of C02 to 02 permeability which
allow 02 concentrations to decrease without an associated excessive buildup of CO2
inside the package (Kader, 1989). Some PVC films can have very high C02/02

permeability ratios (4—5) as well, making them well suited for MAP.

IV. Modeling Atmosphere Modification within the package
Respiration of apple slices described by R02 and p92 as function of temperatures
has not been shown. The effect of temperature on respiratory rate has been measured

for tomato, blueberry, and raspberry fruits (Cameron et al., 1989; Beaudry et al.,

19
1992; Joles et al., 1994). The permeability of the film to O2 and C02 and it’s

temperature sensitivity have to be also experimentally defined so that the living
produce will be able to respire and maintain aerobic condition through out the

temperature range.

A.) Respiratory Models

Respiration rates have been measured for a number of fruits and vegetables
under various conditions as either 02 consumption or C02 production rates. Talasila
(1992) gives a comprehensive list of the available models. Henig and Gilbert (1975)
fitted regression equations for rates of O2 consumption and C02 production as
functions of 02 and C02 concentrations for tomato fruits by assuming that there was
negligible influence of C02 concentration on O2 consumption and 02 concentration on
C02 production. This assumption was not considered valid after the data was
analyzed again by Hayakawa et al. (1975). However, a number of studies have
shown that CO2 has little influence on respiratory activity at levels below 20 kPa
(Beaudry et al., 1992; Joles et al., 1994).

Cameron et a1. ( 1989) developed empirical models for 02 consumption rate as
a function of 02 concentrations from the 02 depletion data from tomato fruit sealed in
jars. Cameron et al., (1989), Mannapperuma and Singh (1987) estimated respiration
rates only at 20C. Talasila et a1. (1992) developed a model to predict respiration rate
of strawberries as a function of temperature and a function of gas concentrations. He

found that the influence of CO2 concentration on respiration rate of strawberries is

20
minimal.

Lee et al. (1991) developed a semi-empirical model for out broccoli based on a
enzyme approach. In this model, the dependence of respiration on 02 was assumed to
follow a Michaelis-Menten type equation, the effect of CO2 on respiration was thought
to follow an uncompetitive inhibition model. This model was later used to predict gas
concentrations inside MA packages of cut broccoli.

A Michaelis-Menten type respiratory model can be well fitted with respiratory
data of several commodities and has been used with various commodities such as
blueberry, tomato, raspberry and strawberry (Banks et al., 1989; Beaudry et al.,
1992; Cameron et al., 1994; Joles et al., 1994; Lee et al., 1991; Talasila et al.,

1994). In these studies the Michaelis-Menten type respiration model is as follows.

01
Vm Pa“ (2)
K7 + Pro2

R02 =

From the above equation, 02 uptake (R0,) depends on 02 partial pressure
inside the package (p.02) and temperature which can be expressed in two parameters;
KT (p.02 at half-maximal R0,) and Vm (maximal R0,). This model, developed by Lee
et al. (1991), was proved to fit well with the real respiratory data of blueberry fruit
(Cameron et al. , 1994). This model appears to have general applicability and has
been shown to be suitable for incorporation into models for predicting the level of 1292

over a range of temperatures.

2 1
B.) Modeling Package Atmospheres

For packaged produce, it was recognized by Tomkins (1961) that several
factors affect 02 and C02 conditions within packages. Factors identified were the
size of package, surface area and weight of contents and the production, escape and
equilibrium concentration of CO2 (Tomkins, 1961). Based on this early knowledge,
there were many attempts to find the relationship between polymer film characteristic
and respiration of commodity in MAP.

Several attempts have been made to model MAP systems for each constant
surrounding temperatures (Cameron et al., 1989; Deily and Rizvi, 1981; Hayakawa et
al., 1975; Henig and Gilbert, 1975; Jurin and Karel, 1963; Mannapperuma and
Singh, 1987; Veeraju and Karel, 1966). Kader (1989) and Talasila (1992) give the
comprehensive list of the available models. The first steady state model to predict gas
concentrations inside a package for apples at constant temperature was developed by

Jurin and Karel (1963). This is simply a form of Fick’s law and a rearrangement of

 

 

equation 1.
R 1
p,°’= [pf’ _"_] M] (3)
PO: A
pco,= pco Rea} 22.414W <4)
I 0 P02 A

 

Where p.02 and p92 are 02 partial pressure inside and outside the package,

respectively in kPa. R6, Rec, are 02 uptake and CO2 production of fruit per unit

22
weight (mmol-kg"°h"). P02 and PC02 are 02 and CO2 permeability coefficient,
respectively in mmol-cm-cm'z-h°‘-kPa“. W is fruit weight in kg. 1 is thickness of film
in cm. A is surface area of the package in cmz.

From the steady-state respiratory model (equations 3 and 4), the relationship
between the rate of 02 uptake and 02 concentration for tomato fruit was described as
a continuous mathematical function which was utilized to develop the model for
optimization of oxygen concentration in the sealed package of tomato fruits (Cameron
et al., 1989; Gong and Corey, 1994). Beaudry et a1. (1992) measured the effect of
temperature on package 02 and CO2 and empirically fitted the relationship between 02
uptake and steady-state 02 of blueberry fruit with exponential equations at each
temperature (0-25C).

The blueberry fruit data generated by Beaudry et al. (1992) was further
evaluated by Cameron et al. (1994), who developed the model for prediction of
steady-state package 02 for MA systems over a wide range of temperature (0-25C).
The model developed has been used to predict the effect of altering the Ea of the film
on p.02 across the temperature range of 0-25 C. Predicted 02 levels agree quite well
with original package 02 data of Beaudry et al. (1992).

The purpose of this research was to determine necessary packaging
characteristics (e. g. package dimensions, film permeability to O2 and C02,
temperature sensitivity of 02 and CO2 permeability, etc) to generate acceptable
atmospheres within packages for sliced apple fruit. The first goal was to determine

target 02 and C02 to control the browning reaction of sliced fruit. The second goal

23

was to collect respiratory data for the development of a respiratory model for sliced
apple such that package characteristics needed to achieve and maintain target gas
concentrations could be identified. To this end, the model was used to predict the
steady-state package oxygen partial pressure as a function of temperature and film

permeability.

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T.M.Stewart. 1989. Modelling fruit response to modified atmospheres. J.K.
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Beaudry, R.M., A.C. Cameron, A. Shirazi, and D.L. Dostal—Lange. 1992. Modified-
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Boylan-Pett, W. 1980. Design and function of a modified-atmosphere package for
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Cameron, A.C., W. Boylan-Pett, and J. Lee. 1989. Design of modified atmosphere
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Cameron, A.C., B.D. Patterson, P.C. Talasila, and D.W. Joles. 1993. Modeling the
risk in modified-atmosphere packaging: A case for sense-and-respond
packaging. Proceeding from the Sixth Intl. CA. conf., Ithaca, N.Y., June 15—
17. NRAES-71(1): 95-102.

Cameron, A.C., R.M. Beaudry, N.H. Banks, and M.V. Yelanich. 1994. Modified-
atmosphere packaging of blueberry fruit: modeling respiration and package
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Sci. 119(3):534-539.

Chen, J .S., C.I. Wei and M.R. Marshall. 1991. Inhibition mechanism of kojic acid
on polyphenol oxidase. J. Agric. Food Chem. 39:1897-1901.

Couey, H.M. and J .M. Wells. 1970. Low-oxygen or high-carbon dioxide atmosphere
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Deily, K.R. and S.S.H. Rizvi. 1981. Optimization of parameters for packaging of
fresh peaches in polymeric films. J .Food Process Engineering. 5:23-41.

Dudley, ED. and J .H. Hotchkiss. 1989. Cysteine as an inhibitor of polyphenol
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Food and Drug Administration 21CFR ch.1(4-1-93 Edition)

Gong S. and K.A. Corey. 1994. Predicting steady-state oxygen concentrations in
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119(3):546-550.

Gran, GD, 1993. Fruit respiration and determination of low oxygen limits for apple
(Malus Domestica, Borkh.) fruit. Master thesis Michigan State Univ., East
Lansing.

Gran, CD, and RM. Beaudry. 1993. Determination of the low oxygen limit for
several commercial apple cultivars by respiratory quotient breakpoint.
Postharvest Biol. Techno]. 3(3):259-267.

26

Hayakawa, K., Y.S. Henig, and S.G. Gilbert. 1975. Formulae for predicting gas
exchange of fresh produce in polymeric films. J. Food Sci. 40(1):186—191.

Henig, Y.S. and S.G. Gilbert. 1975. Computer analysis of variables affecting
respiration and quality of produce packaged in polymeric films. J. Food Sci.
40(5): 1033- 1035 .

Joles, D.W., A.C. Cameron, A. Shirizi, P.D. Petracek, and RM. Beaudry. 1994.
Modified-atmosphere packaging of ‘Heritage’ red raspberry fruit: respiratory
response to reduced oxygen, enhanced carbon dioxide, and temperature. J.
Amer. Soc. Hort. Sci. 119(3):540-545.

Kader, A.A., D. Zagory, and EL. Kerbel. 1989. Modified atmosphere packaging of
fruits and vegetables. Crit.Rev. Food Sci. 28(1):1-30.

Kim, D.M., N.L. Smith and CY. Lee. 1993. Quality of minimally processed apple
slices from selected cultivars. J. Food Sci. 58(5):1115-1117.

Lee, CY. and M.R. McLellan. 1990. Effect of cultivar and composition of phenolics
on browning of apples. Abstract#558, IFT Annual Meeting, Anaheim, CA.

Lee, D.S., P.E. Haggar, J. Lee, and KL. Yam. 1991. Model for fresh produce
reparation in modified atmospheres based on principles of enzyme kinetics. J.
Food Sci. 56(6):1580-1585.

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18(1).

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Wenatchee, WA., July.

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Lozano-de-Gonzalez P.G., D.M. Barrett, R.E. Wrolstad, and D.W. Robert. 1993.
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Mannapperuma, J .D. and RP. Singh. 1987. A computer aided model for gas
exchange in fruits and vegetables in polymeric packages. ASAE paper no. 87-
6526. Paper presented at the 1987 winter meeting of the ASAE at Chicago,
Illinois.

Mateos, M., D. Ke, M. Cantwell, and A.A. Kader. 1993. Phenolic metabolism and
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Mayer, A.M. and E. Harel. 1979. Polyphenol oxidase in plants. Phytochemistry
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McEvily, A.J., R. Iyengar, and W.S. Otwell. 1992. Inhibition of enzymatic browning
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28

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29

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HortScience 21(3):472-474.

CHAPTER II

Modified-atmosphere packaging Of apple Slices: Modeling respiration and
package oxygen partial pressure as function of temperature and film
characteristics.

30

 

 

3 1
ABSTRACT

A systematic approach was taken to acquire information for the design of a
modified-atmosphere packaging (MAP) system for apple slices. Initially, various
combinations of O2 and CO2 were assessed for their control of tissue browning,
thereby generating target gas concentrations for package design. Reduced 02 and
elevated C02 atmospheres were applied to sliced apples and while some gas
concentrations Significantly reduced browning relative to air controls, none of the
treatments prevented browning to a sufficient level to be acceptable. Modified-
atmosphere packaging (MAP) was used as a tool for obtaining respiratory data needed
to calculated permeability characteristics of packaging films that will obtain and
achieve and maintain desired gas levels in the package headspace at 0, 5, 10 and 15C.
The lowest 02' partial pressure to which fruit could be exposed without fermentation
increased with increasing temperature. A mathematical model was developed to
characterize the relationship between, steady-state 02 partial pressure (p.02) and 02
uptake and film permeability to 02 of packages. Maximum 02 uptake (Van) and the p92
at half-maximal 02 uptake (KT) were both increased with temperature. The p92 model
was used for predicting the effect of P02, activation energy (EpO’), temperature, film
type, and film thickness on p.02 for apple slices. It can also be used to predict the
minimum ratio Of Wl/A of LDPE that can achieve aerobic condition throughout the

temperature range.

 

 

32
INTRODUCTION

Lightly processed produce, also known as precut, value-added, fresh-processed
or fresh-cut produce, are packaged produce items that comprise the most rapidly
growing segment of the fresh produce industry. Precut vegetables which include
lettuce, cabbage, broccoli, cauliflower, etc., have found widespread acceptance and
have been readily incorporated into food service offerings. Fruit products, unlike
vegetable counterparts, have been Slower to develop. Sliced fruit with higher sugar
and water contents, have significantly more problems than vegetables because of rapid
tissue browning, moisture loss, decay, and tissue softening. Apple slices has the
potential to be successful lightly process fruit product.

Browning is a major quality concern and, for apple, is primarily.
Discoloration can occur after bruising, cutting or during storage and is often the
limiting factor in shelf life. Browning in a sliced product results from a series of
complex oxidative reactions in part catalyzed by polyphenol oxidase (PPO) (McEvily
et al., 1992). Browning can be retarded by decreasing 02 or increasing C02 in
contact with the cut surface of the product (Siriphanich and Kader, 1985; Kader,
personal communication). Atmospheres with reduced 02 or elevated C02
concentrations have been commonly used to reduce apple respiration and extend
storage shelf life (Rolle and Chism, 1987; Siriphanich and Kader, 1985).

A minimum percentage of (1-3%) 02 is necessary for maintenance of aerobic
respiration. Induction of fermentation results in ethanol and acetaldehyde synthesis,

which can contribute to off flavor development (Rolle and Chism, 1987). Although

 

33

the use of elevated C02 treatments has been Shown to have the desirable effects of
influencing respiration and controlling browning for some commodities, if
concentrations exceed a certain level, injury is likely to occur. Although range of
non-damaging Oz and C02 levels have been published for a numbers of commodities
(Kader, 1989); the safe levels of O2 and CO2 are unknown for apple Slices.

Modified atmosphere packaging can be used to achieve target gas compositions
surrounding a product. The natural process of respiration of the enclosed products
reduces 02 and increases C02 under restricted gas exchange through the polymer film
barrier. Steady-state gas levels achieved in the package depend on the interaction of
respiration of the product and the permeability properties of packaging film.

MA packages should be designed to maintain safe and effective partial
pressures of 02 and C02 over a wide range Of temperatures because there is a risk of
temperature abuse during shipping and handling. The need for an accurate
determination of the lower 02 limit is required for modeling and designing MAP
systems. MA package should be able to provide 02 levels higher than the lower 02
limit and C02 levels below harmful CO2 levels across the temperature range likely to
be encountered.

One approach for designing an MA package that generates desirable package
02 partial pressures is to match total respiratory 02 uptake of the packaged product
with the total 02 permeation through the package according to Fick’s law (Kader,
1989; Beaudry et al., 1992; Cameron et al., 1994). Respiration and film permeability

to 02 and C02 vary differentially with temperature. The respiratory process has the

34
added complexity of also being dependent on the package 0, partial pressure.

The effect of temperature on the respiration rate has been measured for
tomato, blueberry and raspberry fruits (Cameron et al., 1989; Beaudry et al., 1992;
Joles et al., 1994). Respiration of apple slices described by 02 uptake as a function
of temperature and 02 partial pressure has not been defined. However the
dependency of respiration on O2 and temperature has been found to be reasonably
well described by a Michaelis-Menten type equation for tomato (Cameron et a1. ,
1994), blueberry (Beaudry et al., 1992), raspberry (Joles et al., 1994), strawberry
(Talasila et al., 1994) and cut broccoli (Lee et al., 1991). The respiratory models
have been successfully combined with describing the temperature sensitivity of P02 to
develop model for predicting package 02 as a function of temperature, fruit weight,
surface area, film thickness.

The purpose of this research was to determine necessary packaging
characteristics (e. g. package dimensions, film permeability, etc) to generate
acceptable atmosphere within packages of Sliced apple fruit. The first goal was to
determine if there were 02 and C02 combination that controlled browning reaction of
sliced fruit. These gas combinations would then serve of target for package design.
The second gOal was to collect respiratory data for the development of a respiratory
model for Sliced apple. Finally, package permeability characteristics were combined
with the respiratory model to develop a model that can be used to predict the effects
of various parameters (temperature, film thickness, fruit weight. etc) in package 02

such that target gas concentrations could be achieved.

35
MATERIALS AND METHODS

1. Measuring browning in apple slices
A.) Apples

Apple fruit of the cultivar ‘Ida Red’ were harvested in an early October from
Clarksville, Michigan at a stage of maturity suitable for long-term storage under
controlled-atmospheres (CA). They were stored in CA at 1.5 i 0.1 kPa 02 and 3 i
0.5 kPa C02 at 1 i 0.2C. After two months, fruit were removed from CA storage
and held for 1 day in air at 3C prior to the experiment.
B.) Rate of Browning

The rate of tissue discoloration was measured in order to gauge the time when
antibrowning treatments need to be applied at 0, 5, 10, and 15C. Two apples were
sliced into wedges (width 2-3 cm) using a stainless steel knife and placed into jars
with small holes for aeration. The jars were held at 0, 5, 10, and 15C for 3 days.
Browning of the cut surfaces was assessed using the method of Barrett (1989) using
the change in reflectance over time. Measurements were made using the Model CR-
300 Minolta Chroma Meter, (Minolta camera Co.,Ltd, Ramsey, NJ). The ‘L’ value
signifies the degree of lightness from 60 white to -60 (black), ‘a’ and ‘b’ values
signify the color; ‘a’ value varies from 60 (green) to -60 (red), ‘b’ value varies from
60 (yellow) to -60 (blue). Prior to measurement, the Chroma Meter was calibrated

using a white calibration plate.

C.) Inhibition of Browning with CA storage

36
A flow-through CA system, as described by Liu and Samelson (1986) was

used to generate various gas mixtures of O2 and C02. In the study, ten different
mixtures were prepared containing 1 or 20 kPa Oz and 0, 5, 10, 15 or 20 kPa C02.
Apple fruits were cut into wedges (2-3 cm in width) while at 5C using a stainless
steel knife. Bruised tissue was avoided. Four pieces were randomly selected and
sealed into an air-tight 473.2 ml (1 pint) glass container. The jars were flushed
immediately with one of the ten different gas mixtures, and the levels of O2 and C02
in the jar were measured to confirm that they had reached the desired concentration.
Atmosphere modification was completed within 90 seconds after slicing. The jars
were placed in a storage room maintained at 5C and humidified (Liu and Samelson,
1986) gas mixtures were supplied, having a flow rate of 15 ml per minute. Fruit
slice color was determined immediately after cutting and after 1, 2, 3, 5, 7, 10 and
14 days under CA conditions. In each instance, color was determined in three
locations on each face of the four slices for each treatment/time combination.
D.) CO, injury index

A CO2 injury rating system was developed based on visual analysis.
Ratings were on a 1-4 scale (1 =none, 2=slight, 3=moderate, and 4=severe)
(Barrett, 1989). C02 injury was assayed after treatment with the various gas
combinations for 14 days. CO2 injury may be seen as brown and moist surface near

core tissue (Lidster et a1. , 1990)

37

11. Modeling apple respiration and package oxygen partial pressures as a function of
temperature.
A.) Apples

Apple fruit of the numbered selection ‘NY 674’ were obtained from plantings
in Geneva, New York and Clarksville, Michigan. Kim et al. (1993), and Lee and
McLellan (1990) reported ‘NY 674’ tissue showed less decline in ‘L’ values than
other apple varieties and they attributed this resistance to browning as being a result
of lower polyphenol oxidase activity and polyphenol content relative to the other
cultivars tested. This characteristic makes ‘NY674’ a product which Should make
treatments to control browning more efficient. Harvested fruits were held under
elevated humidity at 3C for 7 days prior to use. Apples were cut into wedges using
stainless steelknife. The core of each piece was removed. Each piece was

approximately 1-2 cm wide measured at the skin side.

B.) Package design

Fruit slices were sealed in pouches made of 0.00762 and 0.01016 cm (3 and 4
mil, respectively) thick low-density polyethylene (LDPE; LDF 550) (Dow chemical
company, Midland, MI). The range of steady-state 02 concentrations from 0.1 to 16
kPa were generated at 0, 5, 10, and 15C (Cameron et al., 1989). The initial step in
the designing process involved determining respiration rates for apples at an elevated
02 partial pressure (20.7 kPa) and 20C. From this valve, the R02 was estimated to be

0.1, 0.6, 0.05 and 0.02 mmol kg'1 h'1 at 15, 10, 5,and 0C, respectively. Using these

38

estimates of R0,, the needed film thickness, area and fruit weight was calculated to
generate 16 kPa 02. From these high 02 settings, film thickness and fruit weight
were increased and package area decreased in order to achieve a wide range of lower
02 levels. Four replications of each package configuration were made for each
temperature (Table 1). Film thickness were either 3 or 4 mil and package area either

800 or 1250 cm2. Fruit weight ranged from 19 to 587 g.

C.) Permeability of Film:

The O2 and CO2 permeability of 3 mil and 4 mil LDPE films were determined
on three random film samples at 0, 10 and 20C according to the method of Beaudry
et al. (1992). A specially-built stainless steel permeability cell was submerged in a
water bath (lauda RC20; Brinkrnan Instrument Co., West Bury, N.Y.), and
temperature was measured using thermocouple and mercury thermometers. The
permeability cell contained two circular 25-ml chambers separated by the film sample
and sealed in place by an O-ring. The cell chambers were 8 cm in diameter and 0.5
in depth and surface area 50 cm2. Stainless steel and copper coils tubing were
attached to the inlet for the N2 carrier supply line. The passage of the gas through the
coils before entering the cell allowed the system to be isothermic, i.e. the entering gas
had the same temperature as the cell. The permeant mixture of O2 and CO2 (65 and
35 kPa, respectively) was introduced to one chamber of the cell and N2 carrier gas
was introduced to the other chamber. The rate of O2 and CO2 permeation through the

film was calculated from the steady-state partial pressure difference between the two

39

streams. The partial pressure of O2 and CO2 in the carrier gas stream was determined
from concentration measurements obtained using a sequential combination of O2 and
CO2 analyzers. To measure the 02 concentration, an analyzer with a Ametek S3A/II
a calcia-zirconia electrochemical detection cell was used (Ametek Co., Thermox
Instrument Div., Pittsburgh, Pennsylvania). CO2 was measured with a ADC 225-
MK3 analytical infrared gas analyzer (Analytical Development Co., Hertfordshire,
England). Concentrations were calculated relative to a certified standard gas mixture
(106 uL/L 02 and 100 p.L/L CO2 in N2 gas). Flow rates were maintained between
110 and 130 ml/min for all gases, and the chamber pressures were equalized and
maintained at about 0.4 kPa H20 above atmospheric.

Concentration data were converted to partial pressures using the ideal gas law
to determine the permeability coefficients. Values of the permeability as a function of
the temperature were fitted by an Arrhenius equation or indicated by the following

equation:

Ep

Pr: P. e m (1)

Where Pi is permeability coefficient at any temperature in kelvin. Pc is permeability
constant. R is gas constant (0.0083144kJ-mol'1 K"). Ep is activation energy in

kJ-mol". T is temperature in Kelvin. This equation can be converted to:

1n(P,)=§_I;+1n(P,) (2)

40

E.) Respiration rate of apple slices

Apples were cut into wedges and placed on a plastic tray in order to avoid cut
surface contact with the film. The tray with the slices were placed in LDPE pouches
and heat sealed. A gas-sampling septum, made Of Dupont Silicone H tub/tiling glue
on a short strip of electrical tape was attached to the surface of the package (Boylan-
Pett, 1986).

In order to accelerate the achievement of steady-state gas concentrations, a
portion of the headspace air was removed by vacuum and replaced with N2 gas.
Packages having Obvious holes or containing fruit with decay lesions were discarded.
No fungicide treatment was used.

Gas samples were drawn from each package through the self-sealing silicone
septum using a 0.5 m1 insulin syringe. Two gas samples were analyzed from each
package at each evaluation using the O2 analyzer (Servomex Paramagnetic O;
Transducer, Series 110, Servomex Co., Sussex, England) and C02 analyzer (ADC
analytical infra red C02 Analyzer 225-MK3, Analytical Development Co.,
Hoddesdon, England) connected in series, with N2 as the carrier gas (flow rate = 100
ml/min). A third gas sample was taken if any difference was noted between the first
two samples. I

The gas composition of individual packages was monitored until the internal
gas partial pressure, p.02 and p902 reached steady-state values. For steady-state

conditions the following equations can be written:

 

 

 

R01 = (1200’- pro’) Pg}? (3)
RC0, = (pica, ' paco,) 13:31.4 (4)

The respiratory quotient (RQ) was calculated as R€02 divided by R02. Data
were plotted as the dependence of 02 uptake and CO2 production on O2 partial
pressure in the package (092) at four temperatures. The RQ breakpoint indicating
lower 02 limit was determined from the curve between RQ and O2 partial pressure
using the approach of Beaudry et al. (1992) and an increase in ethanol vapor in the

package.

RESULTS
1. Browning under controlled-atmosphere

Compared rate of browning for cultivar ‘Ida Red’ at 0C and ‘NY674’ at room
temperature, ‘NY674’ even at high temperature (23C) has much slower browning rate
than ‘Ida Red’ at low temperature (Figure l). The browning of apple slices in air as
determined by ‘L’, ‘a’, and ‘b’ value were plotted versus times at five temperatures
(0, 5, 10, 15, and 20C) (Figure 2, 3, and 4). Based on subjective evaluations by
laboratory personnel, changes in ‘L’, ‘a’, and ‘b’ values were 2.8, 1.7, and 4.2,
respectively could be detected. If the value decreased (‘L’ and ‘a’) and increased (‘b’
value) by more than this margin point it was considered to have undergone an

undesirable levels of browning. ‘L’ and ‘a’ values decreased rapidly, while the ‘b’

 

42

value increased rapidly for all temperatures. The relationship between the time (Tm)
required for the reading to reach half way between initial and final value and
temperature was estimated from the best fit curves (Figure 5). Browning occurred
with such rapidity at all temperatures, it was evident that flushing of the mixture gas
would be needed immediately after cutting. ‘L’ and ‘b’ trends indicated the browning
rate was slower at lower temperature. the rate of change in the ‘a’ value was not
much influenced by temperature in the range from O to 15C however, it increased at
20C.

There are Significant treatment effects (oz=0.05) for on ‘L’, ‘a’, and ‘b’ values
(Table 1; Appendix A). CO2 and time (the duration of exposure to treatment
atmosphere) had a significant effect on all ‘L’, ‘a’, and ‘b’ values. Only 02 had a
significant effect on ‘b’ value (Table 2; Appendix A). Exposure to 5, 10, 15, and
20% CO2 caused an increase in ‘L’ value and ‘a’ value relative to CO2 control (5
0.03% C02) (Table 2) but 5, 10, 15, and 20% CO2 did not differ. 5, 10, 20% CO2
caused a decrease in ‘b’ value. The exception being 15% CO2 which didn’t differ
from 5, 10 and 20% C02. There was no apparent pattern to effect of date on ‘L’,
‘a’, and ‘b’ values although there were some differences.

CO2 treatment had a significant effect on the severity of CO2 injury of apple
slices (Table 3; Appendix A). CO2 injury was encountered for 20, 15 and 10% CO2
treatments, it was most severe for the 20% CO2 treatment and there was no

significant difference between 10 and 15% CO2 (Table 3).

43

II. Film Permeability

As previously shown (Beaudry et al., 1992), P02 and Pm2 of LDPE 3 and 4 mil
increased exponentially with increasing temperature (Figure 6). An Arrhenius plot Of
the data indicates that the natural log of the permeability coefficient for both gases
depended linearly on the reciprocal of temperaturein Kelvin (Figure 7) with r2 =
0.99 according to the equation 2, where Ep/R is the slope of the fitted line and ln(P,)
is the y-intercept.

Activation Energy (Epo’) is a measure of temperature sensitivity for 02. The
higher the activation energy, the greater the temperature effect. The degree to which
relative permeability increases in response to temperature (Figure 8) is associated with

its Ep02 according the following equation.

P.

_ £133:
P0

=exp R

 

 

[$153] (5)
Where Pi and P0 are permeability constants at any temperature (1“,) in Kelvin and
273.15 K (To).

The change in the rate of 02 diffusion with temperature for free diffusion is
proportional to the relative change in temperature in Kelvin. The Ep02 of free

diffusion through holes is approximately 5 ldlmol. This low Ep02 confers essentially

no change in gas exchange across the temperature range of this experiment (Figure 8).

Equations for predicting P02 and Poo, for 3 and 4 mil film at any temperature

(Kelvin) were determined to be:

44

4 mil film
P01= 0.077 * exp(—4396/ T) (6)
Pco,= 0.132 * exp(-4157/T) (7)
3 mil film;
P01= 0.104 * exp(—4485/7) (8)
Pco2= 0.167 * exp(-4230/ T) (9)

Regression analysis was performed on transformed data to estimate values of
Ep and, the permeability constant (Pc). When the curves are plotted together, they
are not significantly different for PCO2 and are nearly identical for P0,. The equations

describe essentially the same curve within the temperature range of 0 to 15C.

III. Respiratory model

Steady-state p92 was reached for all packages for each temperature. Steady-
State p.02 ranged from approximately 0.1 to 16 kPa. R02 and Rm, was calculated for
each package using equation 3 and 4, respectively. R02 and RCO2 of apple slices with p02
were plotted as a function of temperature (Figures 9, 10, and 11). The R02 and R€02
increased with increased temperature at all steady-state p.02. The data tended to be

more variable at 10C and 15C.

 

45

AS 1’92 declined, RQ increased above its aerobic values (Figure 12). The 02
level at which this increase took place decreased with temperature. The increase in
RQ with declining p92 has been taken as representing the lower 02 limit (Gran and
Beaudry, 1992) variously referred to as the RQ breakpoint, extinction coefficient and
fermentation point. The low 02 limits for each temperature were determined by
marked increases in RQ values above the aerobic RQ value (approximately 1) which
occurred for packages with declining p.02 (Table 4). Ethanol concentration in the
package headspace increased linearly with RQ above 1 (Figure 13) indicating
fermentative metabolism.

The lower 0, limit estimates for 0, 5, 10, and 15C CT) were empirically fitted

with an exponential equation for graphical depiction (r2 0.99):

Lower 02 limit = 0.195 e‘o'm’“ (10)

The data describing the relationship between R02 and steady-state p92 were
fitted with the Michaelis-Menten type model (Lee et al. , 1991; Cameron et al., 1994)
with two temperature-dependent functions Vm and KT as indicated in the following

equation:

R = m“ (11)
1* Pt

 

Vm and KT were found to vary with temperature according to the follows:

46

Vm= ae”+c (12)

KT= m T+ n (13)
Data were fitted simultaneously at four temperatures using statistical analysis
software (SAS) to estimate values for a, b, c, m, and n as in Table 5. Substituting

these constants in equation 11 yields:

= (0.602e°-°°9T— 0.377) pf” (14)
(0.05T+ 0.662)+ p.01

 

01

The relationship between R0, and p.02 for 0, 5, 10, and 15C was depicted (Figure 15).
At high 1792, R.)2 is considered equal to Vm. This model was well fitted by the data in
Figure 11 with R2 0.944. Vm and KT were calculated from the model (Table 6,
Figures 16 and 17, respectively).

According to the mOdela R02 increased more rapidly with temperature as p92
increased (Figure 18). At 0.3 kPa, R02 increased approximately 3—fold, while at 16
kPa, R02 increased nearly 6-fold. The change in the rate of respiration due to
temperature can be characterized using Q10. Like Bax”, Qlo can be used as a measure
the relative temperature sensitivity of a physiological process. As Qlo increases,
temperature sensitivity increases. Qlo was determined at temperature range between

0-15C at different p92 (Figure 19). For every 10C increase in temperature, the

 

 

47

respiration rate decrease approximate 1.7 to 3.6 times depending on the pp, inside the

package.

IV. The 1792 model
The total 02 uptake of the packaged fruit is given by the multiplication of R02

times the weight, W.

VEu Pfk
KU+ pfh

(15)
o,vv =

R5j‘“’= R W

For a package in which gas exchange is at steady-state, O2 flux into the package (F02,

mmol h") can be calculated from

 

p.” -p."] (16)

At steady-state, Fe, (total 02 flux into the package) is considered equal to respiration
rate total; We can therefore solve for O2 partial pressure inside the package as from

the following equation:

[pf’-pro’]= ——V'““p‘01 W (17)

2

1(1+ 1%0

POA
l

 

which can be rearranged to

48

1/2
2

W] + 4 POO’KT) (18)

K + Vm ~13}
A

 

 

0

2

 

 

 

 

DISCUSSION

While some gas concentrations significantly reduced browning relative to air
controls, none of the treatments prevented browning to a sufficient level to be
acceptable. Kader (personal communication) suggested that 02 levels of 0.5% and
CO2 levels of more than 20% would started to have some effect of controlling
browning on cut fruits. However 0.5 % O2 is dangerously close to the lower 02 limit
for apple fruit slices (0.1 to 0.3%) and a concentration of CO2 greater than 10% can
cause C02 injury.

There are many possible anti-browning treatments that retard tissue browning
apple slices, for example, the combination of sporix; an acidic polyphosphate, with
ascorbic acid (Sapers et al. , 1989), pineapple juice and ion exchange pineapple juice
(Lozano-de-Gonzalez et al., 1993), the combination of 1% ascorbic acid solution with
heat treatment (El-shimi, 1993) as well as honey (Lee et al., 1994). An edible
coating, such as the seaweed-based coating developed by Attila Pavlath (personal
communication) also has potential control browning for 8-14 days. One of these
methods may prove commercially viable depending on the practical processes of

slicing and packing, period of distribution and cost. Anti-browning agents extracted

49

from natural sources may gain favor with some consumer groups. None of them are
successfully used for MA fresh apple slices package in the market.

The anti-browning treatment should be applied to the slices immediately after
it is cut Since color changes rapidly. The optimal concentration and duration Of
chemical treatment for apple slices will probably be cultivar dependent due to
differing browning rates, polyphenol oxidase activities and native antioxidant levels.
It will be important to apply an anti-browning agent in a way that consumes little
time, is of low cost and has high production rate.

Use of this seaweed-based coating is potentially practical way to control
browning in sliced apple. Pavlath (personal communication, 1994) sprayed apple
slices with a seaweed-based coating on surface within 20 seconds. This seaweed-
based formulation has some commercial promise. However, the layer of coating
material (100th of an inch in thickness) may affect consumer’s preference.

Maintenance Of an acceptable texture after cutting, treating with anti-browning
agent and storage needs to be studied. Loss of firmness of apple Slices in atmosphere
can be easily detected by consumer. However, the study of texture changes has not
been done for apple slices in MA package.

Due to the susceptibility of the cut surface of apple slices to decay, a sealed
package or pouch may be necessary. Atmosphere modification is apt to occur once a
package is sealed. Modification of the atmosphere is attained through respiration of
the fruit within the sealed package and depends on the interaction of respiratory

characteristics of the fruit and the permeability properties of packaging film.

50

Therefore, the respiratory data, permeability properties and the levels of pa, and pcoz

limit must be reported.

The lower 02 limit for apple slices was about half (or less) that of whole fruit
(Gran, 1993). The low 02 tolerance of apple slices can be explained by the fact that
whole apple fruit have a skin resistance to 02 movement that is significantly higher
than tissue resistance (Trout et al., 1942; Burg and Burg, 1965). Without the skin
apple tissue (wound tissue) respire more and has higher an internal 02 than whole
fruit at the same p.02 so it needs less 02 to maintain aerobic conditions, thereby
resulting in a decrease in the lower 02 limit.

The low 02 limit of whole apples is temperature dependant (Grans, 1993).
Like whole fruit, the lower 02 increased with temperature for apple Slices. While the
lower 02 limit was defined by an elevated RQ and associated fermentation, there are
also limits imposed by C02 injury. The data suggest the p.902 limit was near 10 kPa
as determined by C02 injury. An optimal package design therefore, will maintain p92
in the range of aerobiosis and p992 below the range causing injury. The p92 model,
based on the respiratory model, can be used to design a package that will predict the
makeup of the atmosphere for sliced apple in any package size, by any polymer film
of known thickness, for any given fruit weight (equation 18). In addition to providing
a suitable atmosphere during storage, packages should maintain safe and, if possible,
effective p.02 and pF°2 over a range of temperatures because of the risk of temperature

abuse during the process of handling and marketing.

 

 

5 1

Optimal package designs will allow sufficient O2 in such that pp, is higher than
the lower 02 limit throughout the temperature range. The Ep02 of LDPE (Figure 8) is
lower than the apparent EaR°2 of apple Slices (Appendix B) throughout the range of
temperatures from 0 to 15C. Thus, the permeation Of 02 gas through the package has
a lower temperature sensitivity than fruit respiration, meaning that as temperature
increased, the respiration rate of the fruit increased relatively more than P02. The
lower 02 limit at which anaerobiosis within the LDPE packages was induced also
increased with temperature ranging from 0 to 15C, thus enhancing the temperature
sensitivity of the system.

Cameron et al. (1993) measured variation in product respiration and package
permeability and modeled the effect on p02. They determined there is an estimatable
risk of the p.02 falling below lower 02 limit and resulting in fermentation. They
showed that for broccoli, packages need to be designed to generate 1292 levels well
above the lower 02 limit in order to ensure aerobic conditions. Target p,°2
concentrations 3-fold higher than the lower 02 limit reduced the risk of a package
becoming anaerobic l in a 1,000,000 (Talasila, personal communication).

The p.02 model developed from apple slice data was used to determine how
changing EaP°2 affects the potential risk of temperature-induced anaerobiosis.
Predictions were made for packages optimized to 0.6 kPa at 0C which provides a
buffer (3X) relative to the lower 02 limit (Figure 20). No Epo2 can provide p.02 above

3X buffered low 02 limit at the higher end of the temperature range. This can be

52

explained by the fact that respiration rate of apple slices increased more rapidly than
the increase in 02 flux through the film.

For packages designed to generate 1.2 kPa at 15C (Figure 21), the lower the
Ep°2, the higher p02 a package will attain at 0C. Polymer films that have lower
temperature sensitivities are predicted to develop greater declines in p92 when the
temperature increased from DC to SC and less flexibility in package design.
Therefore, for package system, the higher the Epo2 the better for the temperature
abuse of the system.

The p.02 model can also be used to demonstrated the effect of film thickness on
p.02 (Figure 22). The predicted curves are for an LDPE package system with fruit 0.1
kg and a surface area of 120 cm2. Films of 0.227 mil thickness or less are predicted
to provide aerobic p.02 levels within the 0 to 15C temperature range. The thicker films
are predicted to risk fermentation over some portion Of the temperature range.

A more generally applicable form of the model can be derived using a ratio of
the Wl/A of each polymer film. From our data, an apple slice package can be
designed to maintain aerobic conditions within the temperature range from 0 to 15C
when the Wl/A ratio is less than 5.65x10'7 kg-mil/cm2 (Figure 23). This ratio is
easily used in designing packages. For example, if a company wished to develop a
100 gram fruit pack and the machines could handle 0.5 to 2 mil thickness of LDPE,
the film dimensions would therefore have to fall within the range of 225 cm2 to 899

cm2 to avoid the risk of fermentation.

53
Ratio 3.575E-07 and 2E-07 were chosen to validate the model at 0, 3, 5, 10,

and 12C. The package pouches were designed for surface area, thickness and fruit
weight according to the predicted ratio. p92 of packages were measured and plotted as
a function of temperature (Figure 24). The data points were reasonably close to the
predicted value (represented by the solid line). However, there were some packages
that were eliminated due to holes in package as determined by an elevated RQ at
steady-state. More packages at each temperature (0 to 15C) should be tested and a
statistical evaluation performed for a more through validation of the model.

Another concern for apple slices package is the package dimension and design.
The primary package needs to be strong enough to prevent the damage from
transportation and distribution that can happen after packing or before consuming.
This design Should be appropriate for the process of packing and handling.

There are many kinds of polymer film available in the market that can be used
for MAP of fresh produce. If company wants to design package that has surface area
120 cm2 exposed to atmosphere and contain 0.1 kg (6 or 7 pieces of 2-3 width
wedge), they model can be used to predict the range of film thicknesses to be used
(Figure 25) to maintain aerobic conditions between 0C and 15C. Among these
polymers, Saran has a high Epoz, but low Po2 so it can achieve a large range of
aerobic p.02. However P02 is very low, so film thickness must be extremely thin.
Since machining has the limitation that the thinnest film that they can produce is 0.4
mil (Steve Jenkins, Dow Chemical, Midland, personal communication) Saran use is

not an option. Moreover, a thin monolayer film may not provide enough strength for

 

54
the package. Film that has low P02, for example LDPE (Po2 = 8.85E-09

mmol-cm-cm‘2 -h"-kPa") or lower, can not be used for product apple slices in this
designed package.

Affinity 1140, an experimental film for Dow Chemical company, is a new
LDPE formulation having precisely controlled frequencies of aliphatic side chains of
specific lengths that has P02 about 3 times higher than that of LDPE with the similar
Epoz. The elevated P02 allows the use of greater film thickness than standard LDPE.
For example, 1 mil frlm will yield p92 of 6 kPa at 0C (film area 120 cm2 and apple
slices 0.1 kg) and will safely remain aerobic until 15C. Affinity 1140 has also has
the advantages of being polyolefin which include high tear strength, high resistance to
chemical degradation, good water barrier, high ratio of PCOZIP02 and good heat seal,
with higher 02 and CO2 permeability (Appendix C).

Decay is one of the major obstacles remaining to the commercial production of
apple slices. Decay was observed on the apple slices in packages within 5 days at
15C and 8 days at 10C. Maximizing this duration will probably be a major goal
marketing to provide sufficient retail and home shelf life after distribution. Types of
microorganisms at each temperature can also be studied.

Decay. control can be achieved through the application of chemical food
additives, irradiation or fungicide however, consumer may prefer the use of natural
preservative compounds. Leepipatanawit (personal communication) is attempting to
use the volatile antifungal compound, 2-nonanone released by red raspberries and

strawberries during ripening (Vaughn et al. , 1993) to control decay in apple slices

55

package. Levels of release of volatile antifungal compounds to maintain target
headspace concentrations can be modeled. An extension of the present model can be
developed which predicts release rate requirements for 2 nonanone or other compound

on the film recommendation generated by the present 1202 model.

References

Beaudry, R.M., A.C. Cameron, A. Shirazi, and D.L. Dostal-Lange. 1992. Modified-
atmosphere packaging Of blueberry fruit: Effect of temperature on package 02
and C02. J. Amer. Soc. Hort. Sci. 117:436-441.

Berrett D.M. 1989. Effects of controlled atmosphere storage on browning and
softening reactions in ’Delicious’ apples. PhD Diss. , Cornell University.

Burg, S.P., and EA. Burg. 1965. Gas exchange in fruits. Physiol. Plant. 18:870-884.

Cameron, A.C., W. Boylan-Pett, and J. Lee. 1989. Design of modified atmosphere
packaging systems: Modelling oxygen concentrations within sealed packages of
tomato fruits. J.Food Sci. 54(6):1413-1416, 1421.

Cameron, A.C., B.D. Patterson, P.C. Talasila, and D.W. Joles. 1993. Modeling the
risk in modified-atmosphere packaging: A case for sense-and-respond
packaging. Proceeding from the Sixth Intl. CA. conf., Ithaca, N.Y., June 15-
17. NRAES-71(1): 95-102.

Cameron, A.C., R.M. Beaudry, N.H. Banks, and M.V. Yelanich. 1994. Modified-
atmosphere packaging of blueberry fruit: modeling respiration and package
oxygen partial pressures as a function of temperature. J. Amer. Soc. Hort.
Sci. 119(3):534-539.

El-shimi, N .M. 1993. Control Of enzymatic browning in apple slices by using
ascorbic acid under different conditions. Plant foods for human nutr. 43:71-76.

Food and Drug Administration 21CFR ch.1 (4-1-93 Edition)

El-shimi, N .M. 1993. Control of enzymatic browning in apple slices by using
ascorbic acid under different conditions. Plant foods for human nutr. 43:71-76.

Gran, CD, 1993. Fruit respiration and determination of low oxygen limits for apple

(Malus Domestica, Borkh.) fruit. Master thesis Michigan State Univ., East
Lansing.

56

57

Gran, CD, and R.M. Beaudry. 1993. Determination of the low oxygen limit for
several commercial apple cultivars by respiratory quotient breakpoint.
Postharvest Biol. Technol. 3(3):259-267.

Joles, D.W., A.C. Cameron, A. Shirizi, P.D. Petracek, and R.M. Beaudry. 1994.
Modified-atmosphere packaging of ‘Heritage’ red raspberry fruit: respiratory
response to reduced oxygen, enhanced carbon dioxide, and temperature. J.
Amer. Soc. Hort. Sci. 119(3):540—545.

Kader, A.A. 1989. A summary of CA requirements and recommendations for fruits
other than pome fruits. Proceeding from the Fifth Intl. CA. conf.,
Wenatchee, DC, June 14-16, vol 1:303-328.

Kader, A.A., D. Zagory, and EL. Kerbel. 1989. Modified atmosphere packaging of
fruits and vegetables. Crit.Rev. Food Sci. 28(1):1-30.

Kim, D.M., N.L. Smith and C.Y. Lee. 1993. Quality of minimally processed apple
slices from selected cultivars. J. Food Sci. 58(5):1115-1117.

Lee, C.Y. and M.R. McLellan. 1990. Effect of cultivar and composition of phenolics
on browning of apples. Abstract#558, IFT Annual Meeting, Anaheim, CA.

Lee, D.S., P.E. Haggar, J. Lee, and KL. Yam. 1991. Model for fresh produce
reparation in modified atmospheres based on principles of enzyme kinetics. J.
Food Sci. 56(6):1580-1585.

Lee C.Y., Smith, D.M. Kim and C. Lagarde de. 1994. Effect of heat treatment on
firmness of apples and apple Slices. J. of food processing and preservation.
18(1).

Lidster, P.D., G.D. Blanpied, and R.K. Prange. 1990. Controlled-atmosphere
disorders of commercial fruits and vegetables. Agriculture Canada Publication
1847/E. pp.7-22.

Liu, F.W. and D. Samelson. 1986. Rates of change in firmness, acidity, and ethylene
production of ‘McIntosh’ apples in simulated low-ethylene CA storage. J.
Amer. Soc. Hort. Sci. 111(3):404-408.

Lozano-de-Gonzalez P.G., D.M. Barrett, R.E. Wrolstad, and D.W. Robert. 1993.
Enzymatic browning inhibited in fresh and dried apple rings by pineapple
juice. 58(2):399-404.

Pavlath A. USDA. Western Regional Research Center. Albany, CA 94710.

 

58

Rolle RS and G.W. III Chirm. 1987. Physiological consequences of minimally
processed fruits and vegetables. J. Food quality. 10:157-177.

Sapers, G.M., K.B. Hicks, J .6. Phillips, L.G. Zarella, D.L. Pondish, R.M.
Matulaitis, T.J. McCormack, S.M. Sondey, P.A. Seib, and Y.S. El-Atawy.
1989. Control of enzymatic browning in apple with ascorbic acid derivatives,
polyphenol oxidase inhibitors and complexing agents. J .Food Sci.

54:997,1002,1012.

Siriphanich, J. and A.A. Kader. 1985. Effects of C02 on total phenolics , phenyl
alanine ammonia lyase and polyphenoloxidase in lettuce tissue. J. Am. Soc.
Hort Sci. 110(1):249-253.

Trout, S.A., E.G. Hall, R.N. Robertson, F.M.V. Hackney, and S.M. Sykes. 1942.
Studies in the metabolism of apples. Austr. J. Exptl. Biol. Med. Sci. 20:219-
231.

Vaughn, S.P., G.F. Spencer, and BS. Shasha. 1993. Volatile compounds from
raspberry and strawberry fruit inhibit postharvest decay fungi. J. Food Sci.
58(4):793-796.

59

Table 1: Weight of fruit(gram), thickness (mils), and surface area (cm2) of
pouches were used to generated range of 02 partial pressure inside the
package at 0, 5, 10, and 15C, calculated from equation 9.

Temperature 0C 5 C

 

pkg Weight(g) Thickness(mil') Area(cm2) Weight(g) Thickness(mil) Area(cm2)

1 475 4 800 578 4 800
2 232 4 800 432 4 800
3 150 4 800 248 4 800
4 107 4 800 1 18 4 800
5 90 4 800 87 4 800
6 72 4 800 66 4 800
7 54 4 800 48 4 800
8 38 4 800 74 3 800
9 53 3 800 54 3 800
10 42 3 800 40 3 800
1 1 47 3 1250 30 3 800
12 27 3 1250 19 3 800
Temperature 10C 15C

 

pkg Weight(g) Thickness(mil) Area(cm2) Weight(g) Thickness(mil) Area(cm2)

1 437 4 800 236 4 800
2 250 4 800 115 4 800
3 139 4 800 76 4 800
4 80 4 800 53 4 800
5 61 4 800 40 4 800
6 9O 3 800 73 3 800
7 67 3 800 56 3 800
8 50 3 800 46 . 3 800
9 36 3 800 52 3 1250
10 27 3 800 35 3 1250
11 31 3 800 28 3 1250
12 20 3 800 21 3 1250

'1 mil = 0.00254 cm

60

Effect of 02,-C02 and time on ‘L’, ‘a’, and ‘b’ values of slice apple
tissue of cultivar ‘Ida Red’ held at 5C. The values of ‘L’, ‘a’, and ‘b’
immediately after cutting were 84.98, 2.55 , and 14.90, respectively.

Table 2:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Oz (%) ‘L’ value ‘a’ value ‘b’ value
1 78.236a 2.38b 23.78a
20 78.05a 2.37a 22.95b
C02 (%) ‘L’ value ‘a’ value ‘b’ value
0.03 77.22b 2.35b 24.06a
5 78.47a 2.39a 22.91c
10 78.36a 2.38a 23.27bc
15 78.36a 2.38a 23.70ab
2O 78.31a 2.38a 22.88c
Day ‘L’ value ‘a’ value ‘b’ value
1 78.75ba 2.39ba 22.95b
2 77.82cd 2.37cd 22.95b
3 78.75a 2.40a 23.08b
5 78.54ba 2.39ab‘ 23.04b
7 78.26cb 2.38bc 23.16b
10 77.26d 2.35d 24.01a
14 77.26d 2.36d 24.33a

 

 

 

 

 

61

Table 3: Effect of CO2 concentration on CO2 injury of apple slices rating from
1-4 scale (1 =none, 2=slight, 3=moderate, and 4=severe) on cultivar

‘Ida Red’ held at 5C.

 

 

 

 

 

 

C02 (%) CO2 injury
0 1.00c
5 1.00c
10 2.00ba
15 1.75b
20 2.63a

 

 

 

 

62

Table 4: Lower 02 limit for apple slices held at 0, 5,10, and 15C. The pp, were

estimated from the curve describing the relationship between RQ and
Oz partial pressure (Figure 13) 02 partial pressure below which a sharp
increase Of RQ took place.

 

 

 

 

 

Temperature Lower 02 limit
(°C) (kPa)
0 0.2
5 0.25
10 0.3
15 0.4

 

 

 

 

 

63

Table 5: Values for a, b, c, m, and n in equation 17 describing the relationship
between 02 uptake and 02 partial pressure inside the package were
fitted simultaneously for 0, 5, 10, and 15C and standard error
calculated by using SAS.

 

Parameters Estimate Asymptotic Std. Error

 

 

 

 

a 0.602 0.257
b 0.069 0.019
c -0.377 0.264
m 0.050 0.033

 

n 0.662 0.398

 

 

 

 

 

64

Table 6: Vm and KT for 0, 5, 10, and 15C calculated from the fitted model;
V,m = 0.602e°'°°9T-0.377 mmol kg" h" and KT = 0.05T + 0.662

 

 

 

 

 

kPa.
Temperature . Vm KT
(°C) (mmol kg" h") (kPa)
0 0.23 0.66
5 0.50 0.91
10 0.80 1.16
15 1.32 1.41

 

 

 

 

 

 

Figure 1:

65

Effect of time on the ‘L’ value, ‘a’ value, and ‘b’ value of Sliced apple
tissue of cultivar ‘Ida Red’ at 0C (closed circle) and cultivar ‘NY 674’
at room temperature (23C) (open circle). Data were fitted with
exponential y = ae""+c. '

'0' value

'L' value

'b' value

66

 

26—
21—
16—

 

 

 

 

2.8—
2.7—
2.6—
2.5-

 

82—:

753—:

 

74$

 

F r I ' I ‘ l ' I ‘ I ' l ‘
0 500 1000 1500 2000 2500 3000

Minutes

 

67

Figure 2. Effect of time and temperature on the ‘L’ value of sliced apple tissue of
the cultivar ‘Ida Red’ in air. Data were fitted with exponential
equation y=ae""+c.

'L' value

68

 

82—
77-

72—

20°C

I
O

 

82—

77—

 

82-

77—

0
CD
C

 

82-

77—

C)
O

 

82-

77-

 

0°C
0 O .

O O

 

I

0

I 500 ' IO'OO' 15'00120100‘25'00150'001

Minutes

 

69

Figure 3. Effect of time and temperature on the ‘a’ value of Sliced apple tissue of
the cultivar ‘Ida Red’ in air. Data were fitted with exponential
equation y=ae""+c

 

'0' value

70

 

 

 

 

 

 

 

 

 

 

 

 

20°C
270— a
A A O
2.50- T .. o
280 I F I T I I T I F 7 T
' " 15°C
2.60- a Q Q a
O V O
280 I I F ' I I F I T I I
' ‘ g 10°C
s
2.60- RG0 O ,.
O" Q U f)
280 I I I I I I I I T I
' 5°C
2m x . ,, A
U V O
U I I I I I I I I I T
0°C
0 (3 L)
2.50— O
l f I F I T I ' I I I ' I I
0 500 1000 15002000 2500 3000

Minutes

 

71

Figure 4. Effect of time and temperature on the ‘b’ value of sliced apple tissue of
the cultivar ‘Ida Red’ in air. Data were fitted with exponential
equation y =ae'”‘+c

 

'b' volue

72

 

 

 

 

 

 

 

 

 

 

26- h A O
\J O U
22-
18“ 20°C
I I I I I I I I I
254 A A a A Q
21-
17- 15°C
I I I l I I I I
25“ n C Q 0 O O
21-
17~ 10°C
V I I I I I I I
26" C O Q 9
22-1 f
18— o
O 5 C
I I I T T F I I I I
26— U 0 O
O
22—
18- 0°C

 

 

I

0

1 500 r1000] 15002000 1250050001

Minutes

 

73

Figure 5. The time (Tm) required for ‘L’, ‘a’ and ‘b’ values to reach half way
between initial and final value of Sliced apple tissue of cultivar ‘Ida
Red’ in air from using the best fit curves of Figures 2, 3, and 4.

 

74

86v oCBGcOQEmH

 

(seinuti/‘i

 

cm A: S m. o

_ ____e___.__________o
o:_o>._ l1.-

o:_o>no|o.

o20>o411<ION

Ice

18

10m

\ a 102

103

 

 

 

75

Figure 6. Effect of temperature on film permeability to 02 and C02 for 3 mil and
4 mil (0.00762 cm and 0.01016 cm) LDPE films used in packaging

.kPO‘Q

Penneobfldy

Onnmtmprxn4h4

1213—07

76

 

1.0E—07—

8.0E—08e

ODE—08-

4.0E—08—

2.0E—08-

 

 

0.0

 

 

T I I I I I I

5 ' I '10 T I '15 I I 20 25
Ternperoture (WC)

 

77

Figure 7. Arrhenius plot of 02 and C02 permeability for 3 and 4 mil LDPE film
used in packaging experiments with r2 = 0.99.

|n(PermeGbility)

-—15.00

78

 

—-II

—16.00-

—l7.00—

—18.00-

—19.00-

 

-20.00

i38c4 mil CO2

    
 

3&4 mil O2

 

 

0.0034

0.0055 ‘ 0.0056
l/Temperoture (K)

0.0037

79

Figure 8. Effect of temperature on relative rate for rates of reaction possesing
range of activation energies including those of the P02 of some films
(Saran, PVC, PP, and LDPE). Data were generated using the
Arrhenius equation (equation 5) and before transformed to a relative
rate of 1 at 0C.

 

Relative RO’te

80

 

60

 

 

 

5 1101

Temperature (°C)

I
l
I
I
l
I
' PVC
I I
O
' €
I
f
I
4 50
I
I O
I
, 0 PP
I ' a
' I I
' I
' I
' o
I ' "
O I '
l O ’
I O
’ O
O O
X ' ' LDPE
o
o ,’ o ‘
O ’ '
l O " o
I O ' "
' ’ o o
O O '0
I ' ‘ a
o ‘ ¢
I a o '0
l o " '0
I o '
I v o a
y I O "
, o 'r '.
I O ' O
o , o ,'
o ' ‘
O O
C I ' 'O
o a o .
v a o
o o
o .,‘
.
" 5
1 I I I —r I I 1 1 T

 

81

Figure 9. The effects of steady state 02 partial pressure and storage temperatures
(0, 5, 10, and 15C) on the rate of 02 uptake of apple slices cultivar
‘NY674’ in sealed LDPE packages.

O2 Uptake (mmo|°kg“°h"‘)

82

 

 

 

 

 

 

 

.- T T I I lo I I a '0
1.4: (boo 00000 15 C
1.0“ o@o
0.6- 332,00?”

lab 0
0.2-8

. I I I I I0 I7' I I '
1.0- o o 10 °C
0.6—‘wm O 00 00 00 O O
0.2- w 0

a) ' I I I I j I I I I
0.7- 5 oc
0.5- 0 (Do 8 O
0.3; we 0 96b 0 g 0
0.1-3g

' . I I I I I I I
0.4— O 0 0 °C

.. O 03 OO

_ O
0.21% acmé’OOOOO coca °°

fiI ‘ I a I I I 1 I . I . I ' I I
O 2 4 6 8 IO 12 14 16 18

O2 Partial Pressure (kPa)

83

Figure 10. Composite curves demonstrating the effects of steady state 02 partial
pressure and storage temperatures (0, 5, 10, and 15C) on the rate of 02
uptake of apple slices cultivar ‘N Y674’ in sealed LDPE packages.

O2 Uptake (mmol-kg‘I-h“)

84

 

 

I I
15C

0
1'6_ A 10C
0 5C 0
1.4— ' 0C 0
O A
1.2% O00 0 O
o
a
1.0— ‘
A
0490
A
08— 000 ‘
4 O 80 p ‘
O A
0.6— 0 AA A ‘
a: ‘0 3 <>
. O ‘A 0 A
04— ‘5 ~00<> I I
‘ (R a Q o o 8 O
-W‘ 66 A . — I.
.4 I
0.2 o I II I.

I I

i.
0.0
0

III
III-1""
I I I I I P I I I I I f I

2 4 6 8 10 12 14
O2 Partial Pressure (kPa)

 

Figure 11.

85

Effect of steady state 02 partial pressure and storage temperatures (0,
5, 10, and 15C) on the C02 production of apple slices cultivar ‘NY 674’
in sealed LDPE packages.

(:02 Production

12-

86

 

1.4—

 

I0>0-

I I I j l I I fl j I i
150 _
10C
SC
0C _.
O o
o 0 —
A
O A _.
O
A
A

<9 0 '8 C"
o [I
I I i I

Il‘l' ‘ —

 

 

 

8‘110T112i11411i6118

O2 Partial Pressure

87

Figure 12. Effect of steady—state 02 partial pressure on the respiratory quotient of
apple slices in sealed LDPE packages held at O, 5, 10, and 15C.

Respiratory Quotient (RQ)

88

 

 

 

 

 

I I I I I I
15°C
I
.0 «'0. o .00 O . o .0 o O
I ' I I v f
., 10°C
0 ' ‘
.§
v
fi'OQ 00‘ o P .. O o 1
a I l l I j T
5 °C
..
I
o -
I
fi“ 0 o .0. o 00.
a I I I r F
0 °C
' o 0 oo o o o 000 -
r I I I 1 fi I j fir I I I I I I T"

 

1 2 , 3 4
OzPartial Pressure (kPa)

89

Figure 13. Relationship between headspace ethanol vapor partial pressure and the
respiratory quotient of apple slices in LDPE sealed packages at four
temperatures.

Ethanol vapor (,uL/L)

9O

 

 

 

 

 

 

 

 

140— I I I 0 I150—
lOO- O -
60‘ o a O —
20- -
M. I I I I
100.: O O 100.

60' O
_ ébo _
20* 0 ..
75_ we . l l l _
- 00 5C -
45- -
lS-l .000 a .—
w CI I I I
30_ OC _
1o- 0 ”O -
O
l’lfimr I I I I
O l 2 3 4

Respiratory Quotient

 

91

Figure 14. Lower 02 limit of apple slices cultivar ‘NY674’ over a range of
temperatures as determined by RQ breakpoint.

92

 

 

 

0.5—1 1 1 1 1 1 1 1 1 1 1 . 1 . 1 1 1 1~
0.4— ,1 _
0.3— ‘ ,/‘ ——
0.2— 0’ i . -—

0.1— -

Lower 02 limit (kPa)
\
\
\

 

 

 

00 I I I I ' l I I I I ' l I l I l '
O 2 4 6 8 10 12 14 16

Temperature (°C)

 

93

Figure 15. Effect of steady state 02 partial pressure and storage temperatuer on the
rate of 02 uptake of apple slices cultivar ‘NY 674’ in sealed LDPE
packages. Curves are depict the best—fit respiratory model for 0, 5, 10,
and 15C (equation 14).

 

94

m: mu fir mm 0.?

Aaniv musmmmua 658a NO

 

 

 

 

 

 

90 o
c. ”.1.“
99 co
9
I a
a
<«
I
I
O '
a o 000
I a
o
_. _ . _ .D. . _ . P . _ __

 

 

 

m;

<l_q.l_5>1.|OLULU) expidn ZQ

95

Figure 16. Effect of temperature on for Vum as determined from respiratory model
with values for a, b, and c as given in Table 5.

 

(mmol'kg“°h“)

mox

V

96

 

1.4-

1.2-

1.0-

0.8-

0.6—

0.4—

O.2~

 

0.0

 

 

5""1'o'

Temperature (°C)

'15

 

 

97

Figure 17. Effect of temperature on for KT as determined from respiratory model
with values for m and n as given in Table 5.

 

98

 

Gov mugauaarcme

 

 

0.0
1N.O
14.0
1©.O
de
Io.—
1N;
14.—

 

 

m;

(0cm) I>1

99

Figure 18. Effect of temperature on the rate of 02 uptake over a range of O2
partial pressure for apple slices. Data were obtained from the fitted 02
partial pressure model (equation 18).

100

 

Gov augaemaEme

 

 

 

 

 

m— OF 0 O
_ _ p _ t . _ . p . _ _ 00.0
md
10¢.Q
P .
10m 0
Iomd
4 100.—
8 18;
cm: _ _ _ _ . _ . _ _ _ _

 

 

044

 

<1..L| l-5>i IOUUUUYOEJ

101

Figure 19. Effect of temperature and 02 partial pressure on Q10 (the rate of 02
uptake at temperature T+ 10C devided by rate of 02 uptake at
temperature TC) of apple slices in the sealed LDPE packages. Data
were obtained from the fitted 02 partial pressure model.

102

Aoov EBaEQEmH

 

 

 

 

 

m: t: N_ O_ m w 4 N o
_ _ .i. . _ _ _ _ _ _ _ _ _ _
1o.m
mto .
00 1mm
..
106..
a.
m: en
en:
_ _ _ _ _ _ _ _ _ _ _ _

 

 

0%

010

 

Figure 20.

103

Predicted O2 partial pressure changes in MA packages of sliced apple
based on initial optimization to 0.6 kPa at 0C for films with various
values for activation energy. Predicted 02 partial pressure inside the
package were generated using Equation 18 with appropriate
substitutions from Equation 14. Film permeability was assumed to
respond temperature as in Figure 8.

 

 

 

Gov EBaEane

 

104

 

 

 

 

m: t.1. N— O_. m an N
1—l— p — — b — — n — _ — p b h — b p _ — — - .i—l— P n —. b b — — u b ~—
m :E: No 532 ,.
OM ll 11 \Ill lllll r
04 11.11.11
om ll ..

 

 

‘-
‘
‘
‘
\
‘
‘
‘
‘
‘
‘
‘
‘
\
‘
‘
‘I
‘

11113:: No 5:2 xn

h b p _ _ p p — F p p — p — _ — b h _ .— P — n — b p . — _ _ _ _ p - . —

 

1 I I
“O. V“. N O.
O O O Q

I

I
09
O

1

I
O.

I

I
(\l

I

.4.
(Odd) ZQ eoadsppeH

 

LO

Figure 21.

105

Predicted O2 partial pressure changes in MA packages of sliced apple
based on initial optimization to 1.2 kPa at 15C for films with different
values for activation energy. Predicted O2 partial pressure were
generated using Equation 18 with appropriate substitutions from
equation 14. Film permeability was assumed to respond temperature as
in Figure 8.

Heodspoce 02 (kPa)

106

 

 

30

4O

50

60

__-——_———__——__~__Ewer Oz limit

 

 

 

I'III

' o

I'IIIIIIIIIII

2 4 6 8"'I'o"1'2'"1‘4

Temperature (°C)

 

 

Figure 22.

107

Effect of temperature on predicted O2 partial pressure for packages of

apple slices composed of LDPE having a range of thicknesses.
Predictions were generated using equation 18 with appropriate
substitutions from equation 14. 3-fold lower 0, limit line was
represents an exponential equation Lower 02 limit= O.587e°*047T fitted
to lower 02 limit estimates Table 4.

 

 

 

108

Heodspoce 02 (kPa)

 

          

02468101214

Temperature (°C) 5'

 

Figure 23.

109

Effect of temperature on predicted O2 partial pressure for packages of
apple slices composed of LDPE, posessing various ratios of Wl/A of
LDPE packages of apple slices. Predictions were generated using
equation 18 with appropriate substitutions from equation 14. 3—fold
lower 02 limit line represents by an exponential equation on Lower 02
limit= 0.587e"'om fitted to lower 02 estimates Table 4.

 

Headspoce 02(kPo)

110

 

20—

I\) O)
l J .

(P

‘555E-07

- 2E-O7 \ .
3575E.7§ ‘

.4
—<
—1

 

5E—O7

7E-O7

 

.
.4
4

_3X lower 02 limit _________________

 

 

I ‘ I ' I I I ' |

'o 2 4 6 811101214

Tenfiperoture (°C)

 

 

 

Figure 24.

111

Validation of the model by designing packages target headspace 02
from 3.575E-07 and 2E-07 Wl/A ratios in Figures 23. 3-fold lower 02
limit line represents by an exponential equation on Lower 02 limit =
O.587e°-°m.

 

 

 

 

112
I I I I f I I I I
20-
16‘. 25-07 0
121 o
: o 8 0
A ' O
O 8“ o
a. ‘ 9
x i
v
4..
N ..
0 3x lower o.__Ii_rp_ig ..................................
8 O I r I I I r I I I I
8- .-
(n 20-
.0 .
O 1
§ 16—
1 2 13.5755-070
8- 8 °
. O o O
. o o
4_ e
. 3X lower 0, limit _________________________________
O T I I I f I

 

 

Temperature (°C)

 

I-

 

 

Figure 25.

113

Effect of ranges of thicknesses of various films on 02 partial pressure
in the package at 0C. Thicknesses noted will provide aerobic
conditions throughout the temperature range shown. Curves were
generated from the fitted 0&2 partial pressure model Equation 18 with
substitution of different Ep , package surface area 120 cm2 and fruit
weight 0.1 kg. Lines parallel x-axis represent the range of thickness of
each film that can be used in aerobic range.

Activation Energy (Ea) for aerobiosis

114

 

 

 

 

 

 

 

 

I 20 ' I . I ' I ' I ' I
1 OO- “
AEROBIC
80- ‘
LLOO43 SARAN 0.00025
60~ ‘
0.00038 PVC 0.000305
0.217 PP 0.021
40 '- 0.277 LDPE 0.0338 —
1.0 AF‘II40 0.124
HYPOXIC
20" (unacceptable) ‘
O - I . I

 

o 4 8'1l21116'210
Package 02 @ 0 °C (CS—fold buffer)

 

CONCLUSION

Browning of sliced apple could not be retarded with Controlled-atmosphere
made of the 02 and C02 combinations tested (0.1 or 20% 02 with 0.03, 5, 10, 15, or
20% C02). Thus, no optimum gas concentrations could be identified. Alternative
methods for controlling browning may be achieved with packaged apple slices by such
method as spraying seaweed-based edible coating. Modified-atmosphere packaging
was used as a tool for obtaining respiratory data needed to calculated permeability
characteristics of packaging films that will achieve and maintain target gas levels in
the package headspace at O, 5, 10, and 15C for cultivar NY‘674’. The lower 02
limits were found to increase with increasing temperature. A lower 02 limit was
determined to be three-fold higher than the O2 limit at RQ breakpoint throughout the
temperature range. This 3 fold buffer was calculated to be a low risk 02 minimum,
having only a 1 in 1,000,000 change of undergoing fermentation. A mathematical
model was developed to characterize the interaction of fruit R02, p92 and P02 film
permeability. Vm increased exponentially with increasing temperature. KT increased
linearly with increasing temperature. The p92 model was used for predicting the effect
of P02, Bap”, temperature, film type and film thickness on p.02 of any package system.

This model can be further used to demonstrate in the minimum ratio of Wl/A that can

115

 

116

achieve and maintain aerobic condition throughout the temperature range. Once the
ratio has been set, packages can be designed for any weight of fruit, thickness of the
film and size of the package. A film with high P02 approximately 1E-08 mmol-cm"
2°h"-kPa'1 (10 times higher than common LDPE) is recommended to be used with
apple slices. Decay is also needed to be controlled in the MAP of apple slices. This
model can be further to predict release rate requirements for antifungal compounds
such as 2 nonanone, based on film recommendation generated by the present p92

model.

APPENDIX A

117

Table 1: Analysis of Variance Procedure for ‘L’, ‘a’, and ‘b’ values

Dependent Variable: L—value

 

 

 

Source l_)_E Sum of Squares Mean Square F-value 2
Model 69 426.493 6.18 3.41 0.0001
Error 210 380.398 1.81

Corrected

Total 279 806.892

Dependent Variable: a—value

Source DE Sum of Squares Mean Square F—value 2
Model 69 0.272 0.0039 3.41 0.0001
Error 210 0.242 0.0011

Corrected

Total 279 0.514

Dependent Variable: b-value

Source m Sum of Squares Mean Square F-value 2
Model 69 412.10 5.972 2.09 0.0001
Error 210 599.172 2.853

Corrected

Total 279 1011.27

118

Table 2: Analysis of Variance Procedure; the effects of each treatment and

between treatments to ‘L’, ‘a’, and ‘b’ values.

Dependent Variable: L-value

 

 

 

__Source M W W m E

02 1 2.4219 2.4219 1.34 0.2489
C02 4 59.923 14.981 8.27 0.0001
date 6 123.84 20.641 11.39 0.0001
02*date 6 57.79 9.633 5.32 0.0001
C02*date 24 88.21 3.675 2.03 0.0044
02*C02 4 10.37 2.593 1.43 0.2247
02*C02*date 24 83.92 3.496 1.93 0.0076
Dependent Variable: a-value

Source DE Sum of Squares Mean Square F-value P

02 1 0.00154 0.00154 1.34 0.2489
C02 4 0.03819 0.00955 8.27 0.0001
date 6 0.07895 0.01315 11.39 0.0001
02*date 6 0.03684 0.00614 5.32 0.0001
C02*date 24 0.05623 0.00234 2.03 0.0044
02"‘CO2 4 0.00661 0.00165 1.43 0.2247
02*C02*date 24 0.05349 0.00223 1.93 0.0076
Dependent Variable: b-value

Source 133 Sum of Squares Mean Square F-value P

02 1 49.97 47.97 16.81 0.0001
C02 4 58.78 14.69 5.15 0.0006
date 6 76.38 12.73 4.46 0.0003
02*date 6 9.96 1.65 0.58 0.7448
C02*date 24 89.80 3.74 1.31 0.1587
02*CO2 4 54.70 13.67 4.79 0.0010
02*C02*date 24 74.51 3.10 1.09 0.3594

 

119

Table 3: Analysis of Variance Procedure for CO2 injury.

Dependent Variable: CO2 injury

 

 

Source m Sum of Squares Mean Square F-value 2
Model 9 16.525 1.836 3.87 0.0024
Error 30 14.25 0.475

Corrected

Total 39 30.775

Dependent Variable: C02 injury

Sourgg DE Sum of Squares Mean Square F-value P

02 1 0.625 0.625 1.32 0.2600
C02 4 15.40 3.85 8.11 0.0001
02 and C02 4 0.5 0.125 0.26 0.8993

 

APPENDIX B

120

Figure 1. Calculated apparent activation energy (EaR°2) for sliced apple fruit
respiration as affected b temperature and 02 partial pressure.
Calculated values for Ea °2 obtained by stepwise numerical integration
of the relationship between 1n(02 uptake) and 1/Temperature in K at 02
partial pressure 0.3, 0.5, 1, 4, and 16 kPa.

121

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1U9J0dd0 D
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(low/M)

APPENDIX C

122
Affinity 1149

Dow Company Texas
Density = 0.895

melt index = 1.6

Ea’°2 = 36.34 kJ/mol
Ea’°°2 = 32.36 kJ/mol
Po2 = 0.254 exp(-4371/T)
Pm2 = 0.25 exp(-3923/T)

PC02/1)o2 = 4.3

 

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