éol’)

 

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This is to certify that the
thesis entitled

THE SHELF LIFE AND IN PACKAGE COOKING OF READY-
TO-EAT FRESH ASPARAGUS IN MICROWAVEABLE MAP
AND VSP TRAY SYSTEMS

presented by
Patnarin Benyathiar

has been accepted towards fulfillment
of the requirements for the

MS. degree in Packaging

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November 9, 2009

 

Date

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THE SHELF LIFE AND IN PACKAGE COOKING OF READY-TO-EAT FRESH
ASPARAGUS IN MICROWAVEABLE MAP AND VSP TRAY SYSTEMS

By

Patnarin Benyathiar

A THESIS

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

MASTER OF SCIENCE

Packaging

2009

ABSTRACT

THE SHELF LIFE AND IN PACKAGE COOKING OF READY-TO-EAT FRESH
ASPARAGUS IN MICROWAVEABLE MAP AND VSP TRAY SYSTEMS

By
Patnarin Benyathiar

Asparagus (Asparagus officinalis L.) is one of the most popular cuisine
vegetables. To assess the quality as a packed ready-to-eat product, fresh green
asparagus (Michigan and Peru) was cut to the length of 6 inches, sanitized with
sodium hypochlorite and then packed in commercially available microwaveable
modified atmosphere packaging (MAP) and vacuum skin packaging (VSP) trays.
Weight loss, moisture content, pH, 02/002 content in the package headspace,
microbial growth and sensory shelf life (odor, color, texture and overall quality)
were analyzed throughout the storage time. Michigan asparagus was packed and
stored at 1°C and 8°C, 80% RH for 18 storage days. The sensory results showed
that the shelf life of asparagus stored under MAP was longer than that stored
under VSP. MAP of asparagus, stored at 1°C and 8°C was able to maintain
product quality through 18 days and 15 days, respectively, whereas the VSP
package maintained product quality for only 9 days at 1°C and 3 days at 8°C.
Asparagus was also stored at a commercial storage temperature (4°C, 80% RH)
for 21 days. The MAP system maintained asparagus quality throughout the 21
days while the VSP system maintained product quality until day 18. Microwave
cooking time and power level affected the quality of the cooked asparagus. Either
2 or 3 min cooking time at full power was satisfactory for the MAP while 2 min at

full or medium power was satisfactory for VSP.

This thesis is dedicated to

My parents, Suchint Benyathian and Sopit Benyathian, my sister
Asaya Benyathian and my grandparents

iii

ACKNOWLEDGEMENTS

I am highly indebted to many people for their help and support throughout
my graduate study. First of all I would like to thank my wonderful advisor Dr.
Bruce Harte for all his consistent support and guidance during this program and
for his encouragement to pursue my MS. degree. He provided me several
opportunities to explore my knowledge in academics and also in several other
fields.

I am also thankful to my committee, Dr. Janice Harte and Dr. Susan Selke,
for their valuable time and invaluable advice. I am greatly indebted to Dr. Janice
Harte who sparked my interest in sensory science and encouraged me for
studies and provided a great opportunity to join internship at Kellogg Company,
Battle Creek.

This project could not be successful without the invaluable suggestion
from another wonderful person, Dr. Mark Ubersax. His role was pivotal to this
research. I also express my sincere thanks to Dr. Kirk Dolan for his kind
permission to use his lab facilities and his advice all the time.

I am grateful to the faculty and staff at the School of Packaging. I would
like to thank Linda Estill and Colleen Wager for their great help. I am also
thankful to Michigan Asparagus Council for funding this project, especially Mr.
John Bakker who provided asparagus for this research.

I am also greatly indebted to all my friends for their friendship and

assistance, specially Dharmendra Mishra, Joongmin Shin, Savisa Bhumiratana,

iv

Chomploen Suwanbhanu, Chaleampong Kongcharoen, Vareemon Tuntivanich,
Thasanee Satimanon, Monthien Satimanon, Pakapol Kittipinyovath, Apiradee
Bhisanbut, Enyo Quist, Lillian Tarazi, Pankaj Kumar, Mitzi Ma, Eric Birmingham,
Eva Almenar, Alliison Meldrum, who helped me to pack asparagus in packages
and also served as trained panelists on sensory panel. I really appreciate their
help during long hours in the pilot plant. I also extend my thanks to all my Thai
friends in packaging.

I am greatly thankful to my family who always taught me the value of
education and encouraged me to pursue my higher studies. They make me feel
that they are always with me and comfort me in tough times.

Please accept my apology if I forgot to mention those who have

contributed to this research. I sincerely thank them from the bottom of my heart.

TABLE OF CONTENTS

List of Tables ....................................................................................... ix
List of Figures ....................................................................................... xii

1 Introduction

1.1 Asparagus Harvest ................................................................ 2
1.2 Asparagus Market ................................................................. 2
1.3 Characteristics of Fresh Green Asparagus ................................. 3
1.4 Nutritional Value of Fresh Asparagus ........................................ 4
1.5 Packaging of Asparagus ......................................................... 5
1.6 Bibliography ......................................................................... 8
2 Literature Review

2.1 Michigan asparagus ............................................................. 10
2.2 Michigan asparagus market .................................................... 12
2.3 Pathogenic microorganisms and degradation of asparagus .......... 14
2.4 Sanitation for fresh-cut asparagus ........................................... 18
2.5 Innovation packaging of fresh-cut asparagus ............................. 29

2.5.1 Modified atmosphere packaging (MAP) ......................... 31

2.5.2 Vacuum skin packaging (VSP) .................................... 38

2.5.3 Film ........................................................................ 39
2.6 Storage and Temperature .................................................... 47
2.7 Sensory quality of fresh-cut asparagus .................................... 52
2.8 Microbiological safety of fresh-cut asparagus ............................ 56
2.9 Bibliography ....................................................................... 61

3 The Shelf Life of Fresh-Cut Michigan Asparagus Packed in MAP and VSP
Microwaveable Tray Systems at 1°C And 8°C Storage Temperatures

3.1 Introduction ........................................................................ 75
3.2 Materials and Methods ......................................................... 77
3.2.1 Sanitation, packaging and storage ................................. 77

3.2.2 Product Evaluation .................................................... 79
3.2.2.1 Weight loss ................................................... 79

3.2.2.2 Moisture Content ............................................ 79

3.2.2.3 Headspace gas analysis .................................. 80

3.2.2.4 pH analysis ................................................... 80

3.2.2.5 Microbial analysis ........................................... 80

3.2.2.6 Sensory evaluation ......................................... 81

3.3 Result and Discussion ........................................................... 83
3.3.1 Weight Loss .............................................................. 83

3.3.2 Moisture Content ........................................................ 84

3.3.3 Headspace gas Analysis .............................................. 86

3.3.4 pH Analysis .............................................................. 88

vi

3.3.5 Microbial analysis ....................................................... 90

3.3.6 Sensory evaluation ..................................................... 94

3.4 Conclusion ......................................................................... 98

3.5 Bibliography ...................................................................... 99

4 Shelf Life of Fresh-Cut Green Asparagus in MAP and VSP Microwavable
Tray Systems

4.1 Introduction ....................................................................... 103

4.2 Materials and Methods ......................................................... 105

4.2.1 Sanitation, packaging and storage ................................ 105

4.2.2 Product Evaluation .................................................... 107

4.2.2.1 Weight loss .................................................. 107

4.2.2.2 Moisture Content ........................................... 107

4.2.2.3 Headspace gas analysis ................................. 108

4.2.2.4 pH analysis .................................................. 108

4.2.2.5 Microbial analysis .......................................... 109

4.2.2.6 Sensory evaluation ........................................ 110

4.3 Result and Discussion ......................................................... 111

4.3.1 Weight Loss ............................................................. 111

4.3.2 Moisture Content ...................................................... 111

4.3.3 Headspace gas Analysis ............................................. 113

4.3.4 pH Analysis ............................................................. 116

4.3.5 Microbial analysis ................................................... 117

4.3.6 Sensory evaluation ................................................... 120

4.4 Conclusion ........................................................................ 121

4.5 Bibliography ..................................................................... 123

5 Sensory Quality of Cooked Ready-To-Eat Fresh Asparagus by
Microwaveable MAP and VSP Tray Systems

5.1 Introduction ....................................................................... 127

5.2 Materials and Methods ........................................................ 129

5.2.1 Sanitation and packing ............................................. 129

5.2.2 Cooking and Sensory Evaluation ................................. 130

5.3 Result and Discussion ......................................................... 132

5.3.1 Modified atmosphere packaging (MAP) tray system ......... 132

5.3.2 Vacuum Skin packaging (VSP) tray system ................... 134

5.3.3 Packaging preference of fresh-cut asparagus ................ 136

5.4 Conclusion ....................................................................... 138

5.5 Bibliography ...................................................................... 139
CONCLUSION ................................................................................... 141
APPENDICES .................................................................................... 143
APPENDIX A Flow Chart of Over All Process ............................... 144
APPENDIX B Consent Form for Sensory Evaluation of Fresh Asparagus.
.............................................................................................. 145

vii

APPENDIX C Questionnaire for Sensory Evaluation of Fresh Asparagus.
.............................................................................................. 149
APPENDIX D Consent Form for Sensory Evaluation of Cooked Asparagus
.............................................................................................. 151
APPENDIX E Questionnaire for Sensory Evaluation of Cooked Asparagus
.............................................................................................. 153

viii

LIST OF TABLES

Table 1.1: The regional production of asparagus including fresh market and

processed from 2005 to 2006 ................................................................... 3
Table 1.2: The sizes of asparagus spears used in grading ............................. 4
Table 1.3: The nutritional value of green asparagus ..................................... 5

Table 2.1: The yearly harvest seasons of Asparagus in North America and South
America .............................................................................................. 1 1

Table 2.2: The percent consumption of asparagus spears utilized as fresh,
canned and frozen in 1997, 2001 and 2005 .............................................. 13

Table 2.3: Some microorganisms which cause spoilage in asparagus ............ 17

Table 2.4: Sanitization methods used to eliminate/reduce the presence of
microorganisms on fresh whole and cut produce ........................................ 19

Table 2.5: The effect of varying pH on the activity of chlorine forms in water.... 25

Table 2.6: Chlorine concentrations generally recommended for postharvest
sanitation of fresh fruits and vegetables .................................................... 28

Table 2.7: Classification of horticultural crops according to respiration rate ...... 30

Table 2.8: The respiration rates of fresh vegetables (C02 production in mg/kg/h)
at different storage temperatures ............................................................ 31

Table 2.9: Threshold levels of 02 and CO2 concentration causing injury to fruits
and vegetables and typical injury symptoms .............................................. 35

Table 2.10: 02 thresholds causing injury for horticultural crops held at typical

storage temperatures ............................................................................ 36
Table 2.11: C02 pressure thresholds causing injury for horticultural crops ........ 37
Table 2.12: Recommended MA conditions for vegetables ............................ 37
Table 2.13: Typical polymeric plastic materials for MAP containers ................. 40
Table 2.14: Permeability of polymeric films for fresh produce ........................ 45

ix

Table 2.15: Polymeric film types used for packaging of MAP produce ............. 46

Table 2.16: The optimum storage condition of whole fruits and vegetables for
MAP ................................................................................................. 50

Table 2.17: Optimal transit temperatures for various vegetables .................... 51

Table 2.18: Descriptors with definitions and references for odor/flavor of fresh
fruits and vegetables ............................................................................ 55

Table 3.1: The moisture content of fresh-cut Michigan asparagus stored at 1°C
and 8°C, 80% RH under MAP and VSP systems during 18 days storage ......... 83

Table 3.2: 02 and C02 concentration in fresh-cut Michigan asparagus in MAP at
1°C and 8°C, 80% RH during storage ...................................................... 87

Table 3.3: Microbial populations on fresh-cut Michigan asparagus stored in MAP
and VSP at 1°C and 8°C, 80% RH during storage ...................................... 91

Table 3.4: Panelist’s response (mean) for fresh-cut Michigan asparagus stored in
MAP and VSP at 1°C and 8°C, 80% RH ................................................... 95

Table 3.5: Effect of storage temperature on sensory characteristics of fresh-cut
Michigan asparagus stored in MAP ......................................................... 96

Table 3.6: Effect of storage temperature on sensory characteristics of fresh-cut
Michigan asparagus stored in VSP .......................................................... 96

Table 4.1: The moisture content of fresh-cut asparagus during storage at
4°C .................................................................................................. 112

Table 4.2: The pH values of fresh asparagus in MAP and VSP stored at 4°C,
80% RH for 21 days of storage .............................................................. 116

Table 4.3: Microbial populations on fresh-cut asparagus stored in MAP and VSP
at 4°C, 80% RH during storage .............................................................. 118

Table 4.4: Panelist’s response (mean) for fresh-cut asparagus stored in MAP and
VSP at 4°C, 80% RH .......................................................................... 120

Table 5.1: Sensory quality of the cooked asparagus in the microwaveable MAP
tray ................................................................................................. 133

Table 5.2: Consumer preference for cooked asparagus in microwaveable MAP
trays at 2 different cooking conditions ..................................................... 134

Table 5.3: Sensory quality of the cooked asparagus in the microwaveable VSP
trays ................................................................................................ 135

Table 5.4: Consumer preference for cooked asparagus in microwaveable VSP
trays at 2 different cooking conditions ..................................................... 136

Table 5.5: Consumer preference for MAP and VSP packages of fresh-cut
asparagus ......................................................................................... 137

xi

LIST OF FIGURES

Figure 1.1: The small, medium and large size grades of fresh asparagus
spears ................................................................................................. 4

Figure 1.2: A schematic representing modified atmosphere packaging and
vacuum skin packaging systems ............................................................... 6

Figure 2.1: The percent of available chlorine at different pHs and water
temperatures ...................................................................................... 25

Figure 3.1: Fresh-cut Michigan asparagus packed in a MAP tray and a VSP
tray ................................................................................................... 79

Figure 3.2: Moisture content of fresh-cut Michigan asparagus stored in MAP at
1°C and 8°C, 80% RH during storage ....................................................... 85

Figure 3.3: Moisture content of fresh-cut Michigan asparagus stored in VSP at
1°C and 8°C, 80% RH during storage ....................................................... 85

Figure 3.4: 02 concentration in fresh-cut Michigan asparagus in MAP at 1°C and
8°C, 80% RH during storage .................................................................. 87

Figure 3.5: CO2 concentration in fresh—cut Michigan asparagus in MAP at 1°C
and 8°C, 80% RH during storage ............................................................ 88

Figure 3.6: The pH of fresh-cut Michigan asparagus stored in MAP at 1°C and
8°C, 80% RH during storage .................................................................. 89

Figure 3.7: The pH of fresh-cut Michigan asparagus stored in VSP at 1°C and
8°C, 80% RH during storage .................................................................. 89

Figure 3.8: Bacterial growth on fresh-cut asparagus in MAP at 1°C and 8°C, 80%
RH during storage ............................................................................... 92

Figure 3.9: The growth of yeast and molds on fresh-cut asparagus in MAP at 1°C
and 8°C, 80% RH during storage ............................................................ 92

Figure 3.10: Bacterial growth on fresh-cut asparagus in VSP at 1°C and 8°C,
80% RH during storage ......................................................................... 93

Figure 3.11: The growth of yeast and molds on fresh—cut asparagus in VSP at
1°C and 8°C, 80% RH during storage ....................................................... 93

xii

Figure 3.12: The sensory quality of fresh-cut Michigan asparagus packed in
MAP tray at 1°C and 8°C, 80% RH during 18 days of storage ....................... 97

Figure 3.13: The sensory quality of fresh-cut Michigan asparagus packed in VSP
tray at 1°C and 8°C, 80% RH during 18 days of storage .............................. 97

Figure 4.1: Fresh-cut green asparagus spears packed in a Dupont® tray using
MAP, and a Cryovac® tray using VSP ..................................................... 107

Figure 4.2: Percent moisture content of fresh green asparagus in MAP and VSP
packages at 4°C, 80% RH during 21 days of storage ................................. 112

Figure 4.3: 02 and C02 concentrations of fresh-cut asparagus stored in the MAP
at 4°C, 80% RH during 21 days of storage ............................................... 114

Figure 4.4: 02 and CO2 concentrations of fresh-cut asparagus stored in the VSP
system at 4°C, 80% RH during 21 days of storage ..................................... 115

Figure 4.5: 02 and CO2 concentration of fresh-cut asparagus stored in the MAP
and VSP system at 4°C, 80% RH during 21 days of storage ........................ 115

Figure 4.6: The pH measurement of fresh-cut asparagus in MAP and VSP at 4°C,
80% RH during 21 days of storage ......................................................... 116

Figure 4.7: The population of total count bacteria on fresh-cut asparagus stored
in MAP and VSP at 4°C, 80% RH during 21 days of storage ........................ 119

Figure 4.8: The yeast and mold population on fresh-cut asparagus stored in MAP
and VSP at 4°C, 80% RH during 21 days of storage .................................. 119

Figure 4.9: The sensory quality of fresh-cut asparagus packed in MAP and VSP
trays at 4°C, 80% RH during 21 days of storage ....................................... 121

Figure 5.1: Fresh-cut Michigan asparagus spears packed in a Dupont® tray using
a MAP technique and a Cryovac® tray using a VSP technique ..................... 131

Figure 5.2: Microwave cooking of fresh-cut asparagus in MAP and VSP trays and
the cooked asparagus sample presented to the panelists ........................... 132

Figure 5.3: Spider plot of the sensory evaluation of microwave cooked asparagus
in MAP trays under 2 different cooking conditions ...................................... 133

Figure 5.4: Consumer preference for cooked asparagus in microwaveable MAP
trays ................................................................................................ 134

xiii

Figure 5.5: Spider plot of the sensory evaluation of microwave cooked asparagus
in VSP trays under 2 different cooking conditions ..................................... 135

Figure 5.6: Consumer preference for cooked asparagus in microwaveable VSP
trays ................................................................................................. 136

Figure 5.7: Consumer preference for overall appearance of fresh-cut asparagus
packed in microwaveable MAP and microwaveable VSP trays ...................... 137

xiv

1. INTRODUCTION

This thesis has been divided into three chapters. Chapter one focuses on
the shelf life of fresh Michigan asparagus using two different techniques:
modified atmosphere packaging (MAP) and vacuum skin packaging (VSP), and
the effect of two different storage temperatures: 1°C and 8°C on the quality of
fresh asparagus. Chapter two focuses on the shelf life of fresh asparagus in
modified atmosphere packaging (MAP) and vacuum skin packaging (VSP)
microwaveable tray systems at a commercial storage temperature of 4 °C. In
chapter three, the effect of cooking time on the quality of cooked fresh cut
asparagus in modified atmosphere packaging (MAP) and vacuum skin packaging
(VSP) microwaveable trays at 4° C was studied. A consumer sensory
acceptance test comprising the following attributes: aroma, appearance/color,
texture, flavor and overall acceptability, was used to evaluate the quality of
cooked asparagus at different cooking times and temperatures. The appearance
of product in these two different packaging techniques was also considered

important for the marketing of fresh asparagus.

1.1 Asparagus Harvest

Asparagus belongs to the Lily family (Asparagus officinalis L.) and has
been cultivated for over 2000 years. However, the original habitat in which
asparagus was grown is cloudy. Asparagus was first known by Greeks and
Romans, and means sprout or shoot in Greek, and was first domesticated by the
Macedonians about 200 8.0 (MAAB 2005).

Asparagus crowns are planted about a foot deep in sandy, clay-loam, peat
or muck solids with a pH 6.0—6.8. Generally, asparagus is planted from seeds
and the first harvesting begins after the third year of transplanting when crowns
have been well established and the plants have developed a strong fibrous root
system (MAAB 2005). The edible part of asparagus is the young shoot,
commonly called the spear. For green asparagus, spears are cut when their
height is eight or ten inches above the soil in early summer by hand snapping or
cutting with a special long—handled knife below the soil surface (Hexamer 1901).
Due to its perishable nature, asparagus has to be cooled immediately by storing
at 0°C (32°F) to 2°C (35.6°F), 95% RH, or through hydrocooling after harvesting
to remove the field heat. Asparagus can be affected by chilling injury if stored at
0°C for more than 10 days, resulting in limp, wilted stalks and darkened spots

near the tips (Lutz and Hardenburg 1968; Mills 2001; Luo and others 2006)

1.2 Asparagus Market
There are two varieties of asparagus in today’s marketplace based on the
color of the spears: green and white asparagus. Green asparagus is more

popular in the US market than white asparagus, which is widely eaten in Europe

and Japan (MAAB 2005). According to the world asparagus report (2004 Food
and Agriculture Organization (FAO) of the United Nations and FAS/China), the
United States is ranked third in asparagus production. In 2005, cultivated land in
the US. in asparagus production was 54,000 acres which yielded 90,200 tons of
asparagus (World Horticultural Trade & U.S. Export Opportunities 2005). The
three largest asparagus producing states in the US. are California, Washington
and Michigan, according to the USDA (2006), as indicated in Table 1.1 (Peirce
1987; MAAB 2005; USDA 2006).

Table 1.1: The regional production of asparagus including fresh market and
processed from 2005 to 2006 (KIeweno 2006; USDA 2007).

 

Area for Yield Per

Area Harvested Production

 

 

 

Harvest Acre
State 2007
2005 l 2006 200512006 20057 2006
Acres th. 1,000 th.

 

California 24,100 24,000 23,000 32 25 770 600

Washington 13,000 9,000 7,500 41 42 532 378

Michigan 12,200 11,700 1 1,500 19 22 232 257
TOTAL 49,300 44,700 42,000 31 28 1,534 1 ,235

 

 

 

 

 

 

 

 

 

 

 

 

 

1.3 Characteristics of Fresh Green Asparagus

Asparagus has a pencil shape, which translates into a long green spear
with tight scale-like leaves and compact tips. The grading of asparagus is based
on its freshness (including color of spears and tips), length, diameter of stalks
and the amount of bruises (MAAB 2005). The definition of freshness from the
USDA is that “the stalk is not limp or flabby”. The characteristics of high—quality
fresh green asparagus are its firm, fairly straight and shiny deep green stalks or
bluish green stalks with a minimum of white stems, and tightly closed and

compact tips. It should also be disease free (UCCE 2006), and the third quarter

of the stalk length should be green (Lipton 1990; US. Department of Agriculture
1997). According to the United States standards for grading of fresh asparagus,
the spear size is identified by its diameter, measuring at a point approximately 1
inch from the butt. The 5 asparagus spear sizes are shown in Table 1.2 and
Figure 1.1.

Table 1.2: The sizes of asparagus spears used in grading (US. Department of
Agriculture 1997)

 

 

 

 

 

 

 

Sizes of Asparagus Spears Diameter
Very small spears less than 5/16 inch
Small spears 5/16 — less than 8/16 inch
Medium 8/16 - less than 11/16 inch
Lam 11/16 - less than 14/16 inch
Very large 14/16 and more

 

 

 

 

Figure 1.1: The small, medium and large size grades of fresh asparagus spears

1.4 Nutritional Value of Fresh Asparagus

Asparagus is one of the most nutritionally well-balanced and most
consumed vegetables in the world. It has a high fiber level and a wealth of
nutrients, and very low sodium and calorie content. Additionally, asparagus is an

excellent source of vitamin A, vitamin B, vitamin C, carotenoids, folic acid,

potassium, copper, and zinc (California Asparagus Commission 2007) as shown
in Table 1.3. Several published research papers describe the benefits of folic
acid as being necessary in blood cell formation, reduction of neural tube birth
defects and protection against liver disease (MAAB 2005).

Table 1.3: The nutritional value of green asparagus (Rubatzky and Yamaguchi
1997)

 

 

 

 

 

 

 

 

 

 

Composition Percent (%) Composition Percent (%)
Water 92.2 Vitamin B1 0.20
Calories 22 Vitamin B2 0.14
Carbohydrate 3.8 Niacin 2
Protein 2.60 Calcium (Ca) 22

Fat 0.21 Phosphorus (P) 67
Fiber 0.77 Potassium (K) 271
Ash 0.79 Sodium (Na) 2
Vitamin A 950 Magnesium Mg) 18
Vitamin C 33 Iron (Fe) 0.8

 

 

 

 

 

 

1.5 Packaging of Asparagus

Due to its high metabolic (respiration) rate, asparagus deteriorates very
rapidly after harvesting. Thus, controlled atmospheric storage (CAS), an
agriculture storage method, is used to extend the shelf life of fresh asparagus by
constantly monitoring and adjusting the oxygen (02) and carbon dioxide (CO2)
level within a gas-tight storage chamber. Modified atmosphere packaging (MAP)
can also be used to maintain the freshness of fresh produce.

Modified atmosphere packaging (MAP) (Figure 1.2) is a packaging
technique used to create a balance between the produce respiration and the gas
permeability of polymeric packaging films to create an optimum atmosphere. In
general, there are 2 types of modified atmosphere packaging: active and passive.

An active modified atmosphere package is established by flushing out the initial

atmosphere within the package and then replacing it with a gas mixture, usually
nitrogen, oxygen and carbon dioxide. This technique is used for O2-sensitive
products such as fresh-cut lettuce or potatoes to slow down enzymatic browning
(Charles and others 2003). A passive modified atmosphere package depends on
the product respiration and the permeability of the package to adjust the
atmosphere in the package passively (Farber and Dodds 1995).

Vacuum skin packaging (VSP) (Figure 1.2) is a newer packaging
technique which can be used for fresh produce to maintain its freshness and
extend its shelf life. It is established by evacuating the air and sealing the

package without deliberate replacement with any gas mixture.

02

*2"- “\ 11 11 11 11 x"-
‘5'5 ‘\-_t-.t—-1_/’

   

  

 

MAP VSP

Figure 1.2: A schematic representing modified atmosphere packaging and
vacuum skin packaging systems

In this study, both passive modified atmosphere packaging (MAP) and
vacuum skin packaging were used to maintain the shelf life of fresh cut
asparagus at 1°C, 4°C and 8°C.

The overall objective of this work was to determine the shelf life of fresh
asparagus using two different packaging techniques and three storage-
temperature combinations. Other objectives included the verification of the

cooking time and temperature for these microwaveable products and to examine

the feasibility of these packages for fresh asparagus in the market. This work will
help to develop packaged fresh-cut asparagus as a value added, ready-to-eat

product using microwavable packaging.

1.6 BIBLIOGRAPHY

California Asparagus Commission. 2007. Consumer information. National
information.

Charles F, Sanchez J, Gontard N. 2003. Active Modified Atmosphere Packaging
of Fresh Fruits and Vegetables: Modeling with Tomatoes and Oxygen
Absorber. p 1736-42.

Farber JM, Dodds KL. 1995. Principles of modified-atmosphere and sous vide
product packaging. Lancaster: Technomic Publishing Company, Inc. 195—
6 p.

Hexamer FM. 1901. Asparagus, its culture for home use and for market; a
practical treatise on the planting, cultivation, harvesting, marketing, and
preserving of asparagus, with notes on its history and botany. New York:
Orange Judd Company. 1-4, 83-99 p.

Kleweno DD. 2006. Michigan Vegetable Summary 2006. National Agricultural
Statistics Service, United States Department of Agriculture.

Lipton WJ. 1990. Postharvest biology of fresh asparagus. Hort Rev 12:69-155.

Luo Y, Suslow T, Cantwell M. 2006. Asparagus. United States Department of
Agriculture-Agricultural Research Service (USDA-ARS).

Lutz JM, Hardenburg RE. 1968. The commercial storage of fruits, vegetables and
florist and nursery stocks.: United States Department of Agriculture,
Agriculture Handbook. 66-94 p.

MAAB. 2005. Welcome to asparagus online. Michigan Asparagus Advisory
Board.

Mills HA. 2001. Asparagus (Asparagus officinalis). University of Georgia.

Peirce LC. 1987. Vegetables: Characteristics, production, and marketing. New
York: Wiley. 173-83 p.

Rubatzky VE, Yamaguchi M. 1997. World Vegetables. Principles, Production and
Nutritive Values. 2 ed: Chapman & Hall. 645-57802 p.

US. Department of Agriculture. 1997. United States standards for grads of fresh
asparagus.

UCCE. 2006. Asparagus facts and recipes. University of California Cooperative
Extension. Agriculture and Natural Resources.

USDA. 2006. Vegetables 2005 summary. National Agricultural Statistics Service.
United States Department of Agriculture. .

USDA. 2007. California Vegetable Review. National Agricultural Statistics
Service. United States Department of Agriculture.

World Horticultural Trade & U.S. Export Opportunities. 2005. World Asparagus
Situation and Outlook. Foreign Agricultural Service, US. Department of
Agriculture.

 

2 Literature Review

2.1 Michigan asparagus

Asparagus (Asparagus officinalis L.), a unique perennial vegetable, is a
member of the lily family (Liliaceae) (Hexamer 1901; Peirce 1987), and is one of
the most consumed vegetables in the world. The United States ranks third in the
world’s biggest asparagus producers and consumers of fresh asparagus with
102,780 tons in 2004, behind China (587,500 tons) and Peru (186,000 tons)
(World Horticultural Trade & U.S. Export Opportunities 2005). The principal
production and consumption in the US. market is green asparagus (Luo and
others 2006).

After California and Washington, Michigan ranks third in the US. in total
asparagus production with approximately 7,700,000 lbs. of asparagus, worth 18
million dollars annually on farmland mostly near the Lake Michigan shoreline in
both the west and southwest areas (Hart and Shelby or between South Haven
and Benton Harbor) of the state because of the moderate temperatures and
loamy soils (MAAB 2005; USDA 2006). In addition, asparagus also ranks third as
the most important Michigan vegetable crop, behind cucumbers and snap beans
(Taylor 1979). Unlike asparagus from other states, Michigan asparagus is
harvested traditionally by hand-snapping above the ground. This snap method
not only requires less labor but also makes the product tender and tasty,
resulting in one of the best asparagus in the United States. The growing season
for Michigan asparagus is very short, starting from late April through July, as

illustrated in Table 2.1 (MDA 2007).

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2.2 Michigan asparagus market

The marketplace for fresh Michigan asparagus is in the northeast and
midwest and is affected by product preference, preparation technique and
consumption habits (Behe 2006). There are many value added products made
from asparagus in today’s market such as pickled asparagus, canned asparagus
and frozen spear/cut asparagus. According to a strategic plan for the Michigan
asparagus industry which was presented at a Michigan State University
workshop (2000), in 1998 total fresh market asparagus was reported to be
4,000,000 lbs. with a value of $2.6 million, while processed asparagus accounted
for 24,000,000 lbs. with a value of $14.9 million. In 2000, the Michigan Asparagus
Advisory Board demonstrated that only 15% of the harvest is purchased as fresh
asparagus in the fresh vegetable section of the grocery store and/or at a
roadside market. 85% of the yield is sold for food processing, about 38% of
which goes to frozen (cuts & tips or spears) and 62% as canned asparagus (cuts
& tips or spears). However, market researchers from MSU showed that the per
capita consumption of fresh asparagus is increasing at a rate greater than other
fresh vegetables while the consumption of processed asparagus is unchanged or
declining. Hausbeck and others (2002) reported that the consumption of fresh
asparagus in the US. market has increased at a compound annual growth rate
of 14% since 1996. The world consumption of fresh asparagus grew rapidly from
1997 to 2005 and this growth was more than canned and frozen asparagus

(Table 2.2) (IAS 2007).

12

Table 2.2: The percent consumption of asparagus spears utilized as fresh,

canned and frozen in 1997, 2001 and 2005 (Benson 2005)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Countries Fresh Can Frozen
2005 2001 1997 2005 2001 1997 2005 2001 1997
Mai i i); h 2

China 38 25 1 30 55 90 32 20 9
India 100 5 0 95 0 0
Indonesia 100 100 100 0 0 0 0 0 0
Iran 100 0 0

Japan 100 97 90 0 3 10 0 0 0
Korea 100 0 0

Malasia 100 100 100 0 0 0 0 0 0
Pakistan 100 O 0

Philippines 100 100 100 0 0 0 0
Thailand 100 98 0 2 0 0

:E'Uropei j . ‘ ‘ ' ‘ ' " ‘

Austria 100 100 0 0 0 0 0 0
Belgium 100 0 2 0 0
Bulgania 100 0 0

Cyprus 100 100 0 0 0 0 0 0
Czech Rep 100 100 0 0 0 0 0 0
Denmark 100 100 0 0 0 0 0 0
Frence 100 100 0 0 0 0 0 0
Germany 99 100 0 0 0 1 0 0
Greece 100 100 0 0 0 0 0 0
Hungagr 100 100 0 0 0 0 0 0
Israel 100 0 0

Italy 99 100 0 0 0 1 0 0
Netherlands 100 100 0 0 0 0 0 0
Norway 100 0 0

Poland 90 90 9 10 0 1 0 0
Portugal 100 100 0 0 0 0 0 0
Romania 100 100 0 0 0 0 0 0
Slovakia 100 0 0

Slovinia 100 0 0

Spain 70 90 20 5 5 10 5 5
Switzerland 100 100 0 0 0 0 0 0
Turkey 100 0 0

United KinLdom 100 100 0 0 0 0 0 0

 

13

 

 

Table 2.2 (continued)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

. Fresh Can Frozen

°°"“t"°3 2005 2001 1997 2005 2001 1997 2005 2001 1997
é'NQrthAfiié'fiiéa'm ? ' " j ' T f‘ ’ T i '
Canada (Ont.) 100 88 0 12 0 0
Costa Rica 100 100 100 0 0 O 0 0 0
El Salvador 100 100 100 0 0 O O O 0
Guatemala 100 100 100 0 0 0 O 0 0
Honduras 100 100 100 0 0 0 0 0 0
Mexico 100 90 90 O 0 O O 10 10
Nicaragua 100 100 100 O 0 O O 0 0
Panama 100 100 100 0 O 0 0 0 0
United states,‘ 7 45 ‘50, ' 150 ‘40 ‘ ‘5‘ .10
California 100 99 99 0 l 1 O 0 0
Washington 65 30 5
Michigan 20 40 40
South America ' .' , " _ 1 ' , T . ,_ ~
flgentina 65 70 7O 20 30 30 15 0 0
Chile 25 50 35 O 0 10 75 50 55
Colombia 30 30 70 7O 0 10
Ecuador 100 90 9O 0 10 10 O O 0
Peru 60 45 35 30 50 6O 10 5 5
Uruguay . 80 80 0 0 20 20
Africa ’ " ‘ i ' i I , ‘
L_Egypt 100 100 0 0 0 0
Morocco 100 100 0 O 0 0
South Africa 55 33 45 67 O 0
Tunisia 100 100 O 0 0 0
Zimbabwe 100 0 0
‘AustralianArea , , A, i 7‘ i ‘
Australia 95 9O 5 10 0 0
New Zealand 40 35 55 50 5 15

 

 

 

 

 

 

 

 

 

 

 

 

2.3 Pathogenic microorganisms and degradation of asparagus

The presence and contamination by parasites, pathogenic and spoilage
microorganisms including bacteria, yeast and mold on fresh produce can happen
in the field before and/or during harvest, and during postharvest handling,

processing, packing and distribution (Zagory 1999). Viruses are also important

14

 

risk microbes (Beuchat 1998). The presence of spoilage and pathogenic
microorganisms on whole and fresh-cut produce can increase the risk of
foodborne disease outbreaks and spoilage, leading to a reduction in fresh
produce quality and creating a safety risk.

In the US, most of the known foodborne illness outbreaks are reported by
consumers who suspect a relationship with the food that they have eaten and the
disease they have (Guzewich and Salsbury 2001). Data from the Foodborne
Outbreak Surveillance System for 1973 through 1997 shows that the
epidemiologic investigation of a produce-implicated illness outbreak, occurring in
two or more cases of the same illness, is associated with uncooked fruits, raw
vegetables, salad and juice (Sivapalasingam and others 2004). More than 50%
of the sources of foodborne illness outbreaks in the US. are unknown between
1973 - 1987 and 1988 -1992. Between 1995 and 1998, nine foodborne disease
outbreaks caused by Salmonella or E.coli O157:H plagued Michigan, Missouri,
California, Washington, Arizona, and Nevada. These epidemics injured more
than 1234 people who consumed fresh vegetable sprouts, especially from alfalfa
and clover seed (Buck and others 2003). Every year approximately 6 to 8 million
people in the US. are affected by foodborne diseases that cause the death of
9,000 people and cost 5 billion US dollars (Altekruse and others 1997).
Consequently, food safety and human pathogens are an increasingly important
consumer health concern.

Common microorganisms found in vegetables are Pseudomonas

(especially members of the P. fluorescens and P. syringae groups, and

15

Xanthomonas campestris), Enrvinia, coryneforms, lactic acid bacteria, (spore
formers, coliforms, micrococci), Salmonella spp., Shigella spp, Y. enterocolitica,
E. coli O157:H7, L. monocytogenes, C. botulinum, B. cereus, yeasts and molds
(FDA/CFSAN 2004). Molds that are related to the spoilage of vegetables
included Botrytis, Alteman'a, Sclerotinia, Colletotn'chum, Rhizopus, Phomopsis,
Ceratocystis, Geothn'chum, Cladospon'um, Rhizoctonia, Phytophthora,
Perenospora, Bremia, Aspergillus, Penicillium, Fusarium, and Mycosphaerella.
Some microorganisms which cause spoilage of vegetables can produce toxic
metabolites, whereas others are human pathogens which can cause a serious
health condition (T oumas 2005). Both bacteria and fungi are able to spoil fresh
produce by secreting pectolytic enzymes which can soften and disintegrate plant
tissues. As a result, that tissue is broken down and will be mushy, which is
referred to as rot. For most vegetables, spoilage can be caused by either fungi or
bacteria when the pH ranges between 5.0 and 7.0, while the spoilage of most
fruits is caused by fungi when the pH is lower than 4.5 (Forsythe and Hayes
1998). Normally, fresh produce has particular characteristics, which influence the
types of spoilage and pathogens which may be present. For example, large
numbers of Lactobacillus and other lactic acid bacteria have been found on
carrots while apples have large numbers of yeasts (Zagory 1999).

For asparagus, the most common postharvest microbial diseases are
bacterial soft rot, Fusarium rot and Phyrophthora rot. The soft rot caused by
Enrvinia carotovora is the most important asparagus market disease. These

bacteria can enter into the plant tissue from out or bruised parts, causing watery,

16

slimy spears and producing a foul odor. Fusarium rot, which is caused by various
Fusarium species, makes asparagus spears soften and discolor. White, fluffy
mycelium may also appear on the asparagus spears. The main characteristic of
the Phytophthora rot disease which is caused by several Phytophthora species is
wet lesions on the spears usually in the area between the bottom of the tips and
butt ends. Penicillium and Botrytis cinerea are also important organisms which
affect asparagus (Toumas 2005). In addition, Aeromonas is a bacterial pathogen
that has been found to cause the spoilage of asparagus (Buck and others 2003)
as shown in Table 2.3.

Table 2.3: Some microorganisms which cause spoilage in asparagus (ASHRAE
2002)

 

 

 

Microorganisms Types of spoilage Syndrome

 

Bacteria

.4. .

 

Mushyi soft, water-soaked areas

Erwrnra carotovora 30ft rot bacteria on tips and cut ends of asparagus

 

 

 

Aeromonas

 

'Fungi
B. cinerea Gray mold rot
Geotn'chum candidum Sour rot

 

 

 

Water-soaked areas, changing
stalks through yellow to brown
color, principally on asparagus
tips; white to pink delicate mold
Large, water-soaked, or brownish
Phytophthora Phytophthora rot wound at the side of cut
asparamis stalks.

Fusarium Fusarium rot

 

 

 

 

 

 

17

2.4 Sanitation for fresh—cut asparagus

Raw fresh fruits and vegetables must be washed and sanitized before
packing to reduce the number of pathogens which may cause infection, and to
maintain the fresh produce quality. Hazard Analysis Critical Control Point
(HACCP) programs have been developed to control contamination and
outbreaks of foodborne diseases and to reduce the risk of illness related to
consumption of fresh fruits and vegetables. Hygienic processing operations and
sanitization is essential in the food industry, especially for fresh-cut produce
because of the interruption of the natural protective skin, which can result in
increased pathogen growth. Unsanitary equipment, processing surfaces and
working areas, and inappropriate handling can also lead to an increase in the
population of microorganisms on fresh produce, affecting the quality and safety
of the product (Brackett 1992 ). The reduction or elimination of the microbial load
on fresh-cut fruits and vegetables depends on the types of fresh produce and
natural microorganisms (Senter and others 1985). Contact time between product
and sanitizer, concentration of sanitizer and pH also affect the effectiveness of
sanitizer (Pirovani and others 2004). Several methods have been used to
decrease the populations of microorganisms and have different advantages and
disadvantages even if they provide the same result in cleaning and disinfection

as demonstrated in Table 2.4 (Troller 1993; Parish and others 2003).

18

 

 

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Chlorine (hypochlorite) is a very powerful oxidizing agent and one of the
most widely used sanitizers in the food industry. Chlorine was first discovered in
1774 by Carl Wilhelm Scheele (Betz Laboratories Inc. 1980). In 1894, chloride
was used to treat water in Germany and in the early 1930s it was added to wash
water for food processing equipment in the US. After World War II, chloride was
recognized to reduce microbial counts in food products. This was the start of the
use of chlorination in food processing (Troller 1993). The main benefits of using
chlorine are not only that it is a convenient and inexpensive sanitizer for use
against many foodborne pathogens but it can efficiently kill a broad range of
pathogens and microorganisms as well. Moreover, chlorine leaves very little
residue or film on the product’s surfaces (Ritenour and others 2000; Ritenour and
others 2002). The bactericidal action of chlorine is not fully understood. In theory,
bacterial cells are killed by the irreversible chemical reaction of chlorine which
affects the bacteria cell’s enzyme systems (Betz Laboratories Inc. 1980) while
others claim that the bacteria present in water are destroyed as a consequence
of breathing problems caused by the activity of the chlorine.

Two types of tests are available to test for chlorine, total chlorine and
available chlorine. Total chlorine means the total available and combined chlorine
in the water which is still able to disinfect and oxiditize organic matter.
Conversely, available chlorine, also known as reactive chlorine and free chlorine,
refers only to the amount of any chlorine forms available for oxidative reaction
and disinfection. Thus, available chlorine does not include chlorine which is

combined with ammonia or other less readily available chlorine forms such as

22

chloramines which have weak antimicrobial activity (Betz Laboratories Inc. 1980;
Suslow 1997; Suslow 2000).

Chlorine is available in several different forms. Three main commercial
forms of chlorine are approved for use by the US. Environment Protection
Agency (EPA): Chlorine gas (Clz), calcium hypochlorite (CaClzoz) and sodium
hypochlorite (NaOCI) (Suslow 2000; Ritenour and others 2002).

Sodium hypochlorite (NaOCl) is commonly used by the food industry as a
disinfectant to reduce the initial microbiological load since it has powerful activity
against sport-forming resistant microbes. Sodium hypochlorite is usually used in
available concentrations as 5.25 or 12.75% active ingredient. Chlorine is very
soluble in water. When sodium hypochlorite is added to water, a chemical
reaction occurs to separate it into three forms of the chlorinated water: a mixture
of chlorine gas (Clz), hypochlorous acid (HOCI) and hypochlorite ions (OCI'). In
the chlorine water, hypochlorous acid (HOCI) is a much more effective
bactericide than the hypochlorite ion. Thus, hypochlorous acid is the form of

chlorine that will kill pathogens (Suslow 1997; Parish and others 2003).

NaOCl + H20 <—> (mu: Na+ + OH‘

HOCI H H*+.

HOCI + HCl <—> H20 +@

The amount of hypochlorous acid and hypochlorite ion in the chlorine
water is related to the pH of the water. Generally, sodium hypochlorite rapidly
increases the pH of the water to above 7.5. As shown in Table 2.5 and Figure 2.1,

at a pH of 4.5 — 5.5, 100 % of chloride exists as hypochlorous acid (HOCL) and is

23

very effective but is also very corrosive to equipment and its activity is rapidly lost.
At a pH of around 6.0 to 6.5, 98-95% of chlorine (hypochlorous acid) is still able
to be effective against microorganisms. At a pH of 7, about 78 - 80% of the
chlorine is available as hypochlorous acid and at a pH of 7.5 only about 50%
exists as hypochlorous acid. When the pH of the chlorine solution (in water) is
above 8, the hypochlorous acid acts slowly and is only slightly effective against
pathogens. Therefore, the pH is an essential factor, affecting the efficiency of
chlorine and determines the amount of chlorine to be added to reduce the growth
of bacteria. Thus, the higher the pH, the more chlorine is required to kill
pathogens in a water system (Troller 1993; Suslow 1997; Suslow 2000; Sargent
and others 2000 ; Ritenour and others 2002).

In general, pH values between 6.0 and 7.5 are used in sanitizer solutions
because they not only yield acceptable chlorine efficacy to kill pathogens, but as
well reduces the corrosion of equipment (Parish and others 2003). Suslow (1997)
recommended that a pH of between 6.5 and 7.5 is the best compromise of
activity and stability. Consequently, both pH and free chlorine must be carefully
controlled and measured when sodium hypochlorite is used in water (Plotto and
Narciso 2006). Also, the chlorine water must be changed more frequently
because water not only becomes dirty from build up of organic matter but

accumulation of salt can occur due to continuous adding of sanitizer.

24

Table 2.5: The effect of varying pH on the activity of chlorine forms in water

(UCANR 1997)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Approximate % of Approximate °/o of
pH Of process water chloride as HOCL chloride as OCL'
3.5 90 0
4.0 95 0
4.5 100 Trace
5.0 100 Trace
5.5 100 Trace
6.0 98 2
6.5 95 5
7.0 78 22
7.5 50 50
8.0 22 78
8.5 15 85
9.0 4 96
9.5 2 98
10.0 0 100
100 W.
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Solution pH

Figure 2.1: The percent of available chlorine at different pHs and water
temperatures (University of Florida 2000)

Fresh fruits and vegetables have different natural pathogens and varying

microbial loads. The sensitivity of microorganisms to chlorine is also different. For

25

example, bacteria are usually more sensitive to chlorine than mold spores. The
ability of chlorine to control microbial growth on produce is also dependent upon
the concentration of chlorine and contact time of produce in a chlorine water
solution (Suslow 1997; Suslow 2000; Parish and others 2003).

The current lFAS recommendation for using chlorine to sanitize fresh fruits
and vegetables is 100 — 150 parts per million (ppm) of available chlorine with
controlled water pH between 6.5 -—7.5. Rienour and others (2000), Sarget and
others (2000) and Parish and others (2003) reported that the amount of liquid
chloride and hypochlorite needed to sanitize fresh produce and processing
equipment is 50 - 200 ppm for 1 — 2 minutes contact time with pH values
between 6.0 and 7.5. The temperature of the sanitizing water should be at least
10°C (50°F), higher than the temperature of the produce to decrease the
penetrative opportunity of microorganisms. The product sensitivity to bleaching,
however, needs to be considered as it affects consumer acceptance and product
quality since the toleration level of fresh produce to the concentration of chlorine
is different.

Generally, microbial population reduction data have been shown as
logarithms rather than percentages as Iog1o (CF U/g) values. Log reductions of 1,
2, 3, 4, 5 are equal to percentage reductions of 90%, 99%, 99.9%, 99.99%, and
99.999%, respectively (Sapers 2001). Several research papers have shown that
chlorine can generally reduce the initial microbial counts around 1 to 2 log units

(Cherry 1999; Parish and others 2003).

26

Park and Beuchat (1999) showed that sanitation with 2000 ppm sodium
hypochlorite for 3 minutes can reduce the population of E.coli O157:H7 or
salmonellae inoculated on the surfaces of cantaloupe and honeydew melons
between 2.6 and 3.8 log CFUs compared to water wash control, but this
treatment was less effective when applied to asparagus spears. The use of 1%
hydrogen peroxide (H202) with whole cantaloupes, honeydew melons, and
asparagus spears was less effective at reducing the levels of inoculated
salmonellae and E. coli O157:H7 than hypochlorite, acidified sodium chlorite or
peracetic acid-containing sanitizer. Suslow (1997), however, found that chlorine
concentrations exceeding 250 ppm may affect the asparagus and celery surface
by creating light-brown pits, the appearance of bell peppers was not effected. For

asparagus, around 125 - 250 ppm is recommended, as shown in Table 2.6.

27

Table 2.6: Chlorine concentrations generally recommended for postharvest

sanitation of fresh fruits and vegetables (Suslow 1997)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Vegetables 8. Fruits Total Available Chlorine (mg/L)
Artichoke 100 - 150
Asparagus 125 —-250
Bell Peppers 150 — 400
Broccoli 100 — 150
Brussel sprouts 100 - 150
Cabbage (shredded) 100 — 150
Carrots 100 - 200
Cauliflower 100 - 150
Celery 100 - 150
Sweet com 75 — 100
Chopped leafygreens 100 - 150
Cucumbers 100 — 150
Garlic (peeled) 75 — 150
Lettuce-Iceberg flvhole and shredded) 100 — 150
Mushrooms 100 - 150
Green Onions 100 — 150
Peppers (chili or bell) 250 — 400
Potatoes (red or brown) 200 — 300
Potatoes (white) 100 — 250
Pumpkins 100 - 200
Radishes 50 — 150
Spinach 75 — 100
Sweet Potatoes 100 — 150
Squash (all types) 75 — 100
Tomatoes 200 - 350
Turnips 100 - 200
Yarns 100 - 200
Apples 100 — 150
Cherries 75 — 100
Grapefruit 100 — 150
Kiwi 75 - 100
Lemon 40 - 75
Oranges 100 — 200
Peaches, Nectarines and Plums 75 - 150
Pears 200 - 300
Prunes 100 — 150

 

ppm = parts per million (1ppm = 1ug lml = 1mg/l)

28

 

2.5 Innovation packaging of fresh-cut asparagus

Fresh-cut produce is an increasingly popular product and has been
successful in the market as a ready-to-eat product due to the consumer’s interest
in convenience, functional nutrition and healthy food. Consequently, the fresh-cut
fruit and vegetable industry is growing rapidly (Garrett 2002). According to the
lntemational Fresh-Cut Produce Association (IF PA 2003), US. fresh-cut produce
rose approximately from $5 billion in 1994 to $10-12 billion in 2000. Fresh
vegetable consumption grew from 162 pounds in 1987 to 196 pounds in 2000
(Calvin and others 2001). Several organizations including WHO, FAO, USDA and
EFSA have suggested that consumption of fresh fruits and vegetables can help
to reduce the risk of cardiovascular disease and cancer (Allende and others
2006)

Unlike other food products, fresh-cut fruits and vegetables still breathe
after harvesting since the living plant tissues in fresh fruits and vegetable are still
alive and continue the process of respiration. Respiration is a basic plant reaction
by which plants take in oxygen (02) and give out carbon dioxide (C02). During
respiration, plant materials such as carbohydrates, proteins and fats are broken
down by oxygen from air into simple end products (carbon dioxide and water)
with a release of energy as explained by the chemical reaction:

C5H1206 + 602 —> 6C0; + 6H20 + energy

The respiration rate of harvested produce depends on the deterioration

and shelf life of fresh fruits and vegetables, causing the loss of food value, flavor

and weight. Thus, high rates of respiration are associated with short shelf life

29

(FAO 1989; Wilson and others 1999). Different types of fresh produce vary in
their respiration rate depending upon species, variety, growth, harvest and
storage history. Thus, fresh fruits and vegetables are classified according to their
respiration rate as indicated in Table 2.7.

Asparagus is a vegetable which has a very high respiration rate as shown
in Table 2.7 and 2.8. It has a high metabolic rate: > 60 mg COz/kg/h (Fallik and
Aharoni 2004) and the spears deteriorate rapidly. According to the USDA, fresh
asparagus is very perishable and deteriorates above 41°F (5°C). Papadopoulou
(2001) found that the respiratory activity and ethylene production of green
asparagus rose after harvest because of the wounding stress from cutting.

Table 2.7: Classification of horticultural crops according to respiration rate (Fallik
and Aharoni 2004)

 

Respiration Rate

 

 

Class at 5°C Commodities
(mg COglKg-hr)
Very low < 5 Dates, Nuts, Dry fruits
Low 5 - 10 Apple, Celery, Citrus fruits, Garlic, Grape,

Kiwi, Onion, Persimmon, Pineapple, Potato,
Sweet Potato, Watermelon

 

Moderate 10—20 Apricot, Cabbage, Cantaloupe, Carrot,
Cherry, Cucumber, Fig, Gooseberry, Lettuce,
Nectarine, Olive, Peach, Pear, Pepper, Plum,
Tomato, Banana

 

 

 

 

 

 

High 20 — 40 Avocado, Cauliflower, Lima bean, Raspberry

Very high 40 — 60 Artichoke, Bean sprouts, , Green onion, Snap
beans

Extremely > 60 Asparagus, Mushroom, Parsley, Peas, Sweet

h'gh corn, Broccoli

 

 

30

Table 2.8: The respiration rates of fresh vegetables (C02 production in mglkg/h)

at different storage temperatures (Kader 1992 )

 

 

 

 

 

 

 

 

 

 

 

 

Temperature °C)

P'°d"°° o 5 1o 15 20
Asparagus 28 44 63 105 127
Calabrese 42 58 105 200 240
Brussels sprouts 17 30 50 75 90
Lettuce 9 1 1 17 26 37
Tomatoes 6 9 15 23 30
Onions - - 6 - 6
Potatoes - - 4 - 6

 

 

 

 

 

The characteristics of fresh-cut produce such as respiration, lack of
protective skin and damaged tissue from processing make it a very perishable
product. To market fresh-cut asparagus in the fresh-cut marketplace,
improvements in processing technologies and in packaging techniques are

needed to prolong its shelf life.
2.5.1 Modified atmosphere packaging (MAP)

Concern about the preservation of the postharvest quality of fresh fruits
and vegetables is increasing. Since fresh produce still respires after harvest,
resulting in aging and spoilage, the key to extend its shelf life is to slow down its
respiration rate. Several research papers have shown that elevating the carbon
dioxide (C02) gas concentration and decreasing the oxygen (02) gas
concentration helps to inhibit the natural respiration of fresh produce, ethylene

biosynthesis and aerobic microbial growth (Gonzalez-Meler and others 1996).

The first scientific research on the effect of modified atmosphere on

harvested horticultural products was done by J.E. Berard in the 1800s (Dilley

31

1990) and the effect of atmosphere on fruit ripening was studied in 1820 (Floros
1990). The first implementation of this valuable packaging technique was around
1922 in London, England, by focusing on the effect of different concentrations of
carbon dioxide and oxygen on the germination and growth of fruit-rotting fungi at
different temperatures (Brown 1922). Later, in 1930, several research studies
were done to investigate the effect of different concentrations of carbon dioxide
and storage temperature as related to microbial inactivation on fresh meat
surfaces such as beef, pork, bacon, fish and lamb (Ooraikul and Stiles 1991).
The first models used to describe the gas exchange characteristics in MAP were
published in the 1960s. In the US., MAP of fresh-cut fruits and vegetables has
been a popular and fast growing packing technique since the 1990s (Blakistone
1998). Tomatoes, peppers, apples and leeks are successful examples of fresh
produce using MAP to extend the shelf life, without harmful effect on the product

quality (Geeson 1988).

Consumer demand for ready-to-eat fresh produce is rapidly increasing,
especially for the group of consumers who are concerned about convenience,
residues of pesticides, additives and preservatives. Modified atmosphere
packaging (MAP) has become a useful technology for the purpose of extending
the storage shelf life and increasing the commercial value of fresh fruits and
vegetables enclosed in the packages (Moleyar and Narasimham 1994;

Amanatidou and others 1999).

32

Modified atmosphere packaging (MAP) is a technique in which an
alteration in the gaseous composition surrounding the product takes place to
prolong the shelf life of the product by creating a gas atmosphere inside the
package. A wide-range of polymer film styles are used to preserve the freshness
and quality of fresh fruits and vegetables (Thompson 1998). MAP uses the
simple method of gas flushing to remove the air inside the package and then
replaces it with the desired gases. No further control of the initial composition in
the package is necessary. There are three main gases used in MAP to control
and extend the shelf life of products: carbon dioxide (CO2), oxygen (02) and
nitrogen (N2). The choice of gas depends upon the product type (Coles and
others 2003). Research studies show that superatmospheric 02 concentrations
may have no effect in reducing respiration rates and ethylene production
depending on the commodity, maturity and ripeness stage, time and temperature
of storage. However, high 02 concentrations inhibit the growth of some bacteria
and fungi and they are much more effective when combined with C02 gas (15-
20 kPa) (Kader 2000). Amanatidou and others (1999) reported that the inhibitory
effect on microbial growth of ready-made salads is extremely variable when a
high level of only one gas, 02 or CO2, is used. The growth of microorganisms is

significantly reduced when the two gases are applied in combination.

Fresh fruits and vegetables have their own specific characteristics and
behave differently depending upon the gas composition in the package. Due to
the active respiration of fresh produce, chemical reactions and microbial activity,

the gaseous composition inside the package changes constantly and is often

33

difficult to predict and control (Ahvenainen 1996). Atmospheres with too low
oxygen levels and/or too high carbon dioxide concentrations can cause
fermentation which is linked to the development of off-flavors and/or tissue injury,
resulting in accelerated deterioration (Kader 1989b). A study on fresh broccoli
showed a low 02 level helps to retard yellowing of broccoli; however, undesirable
flavor and odor develops when the 02 level goes below 0.25 KPa 02 at 5°C. The
browning of sliced lettuce is retarded when 02 is below 1 kPa at 5°C but
fermentation begins when the 02 falls below 0.3-0.5 kPa. Thus, 0.5 to 1 kPa of
02 is recommended to decrease the browning of lettuce, without causing

induction of fermentation (Cameron and others 1995).

To avoid adverse physiological damage or undesirable effects and to
improve the storability, it is, therefore, important for package designers to
understand the requirements of fresh fruits and vegetables and their safe levels
of 02 and C02. Several researchers have reviewed the limit levels of 02 and C02.
When the 02 level drops below the 02 tolerance value and/or the C02 level
increases above the CO2 tolerance level, damage and injury symptoms may
occur, as shown in Tables 2.9, 2.10 and 2.11. For fresh asparagus, the tolerance
level of C02 concentration is less than 10% at 3-6°C and less than 15% at 0-3°C
storage temperatures. 02 levels less than 10% lead to discoloration of asparagus
(Kader 19893; Saltveit 1989; Ooraikul and Stiles 1991; Kader AA. 1993.). The
recommended levels of 02 and C02 to use to maintain the quality attributes of
fresh asparagus are 21% 02 (air) and 5-10% C02 at a storage temperature of 0-

5°C as indicated in Table 2.12 (Kader 1985).

34

Table 2.9: Threshold levels of 02 and C02 concentration causing injury to fruits
and vegetables and typical injury symptoms (Kader 1989a; Kader 1993;
Thompson 1998)

 

 

 

 

 

 

 

 

 

 

 

 

 

Crops C02 injury C02 injury 02 injury 02 injury
level symptoms level symptoms
Asparagus > 10 % Increased < 10% Discoloration
at 3-6°C elongation, weight
> 15 % gain & sensitivity to
at 0-3°C chilling and pittinL
Avocado > 15 % Skin browning, off < 1% Internal flesh
flavor breakdown, off
flavor
Banana > 7 % Green fruit < 1% Dull yellow or
softening, brown skin
undesirable texture discoloration,
and flavor failure to ripen,
off flavor
Green > 7 % Off-flavor < 5 % Off-flavor
bean more than more than
24 hrs. 24 hrs.
Cabbage > 10 % Discoloration of < 2 % Off-flavor,
inner leaves increased
sensitivity to
freezing
Cucumber > 5% at 8°C Increased softening, < 1 % Off-odor,
> 10% at 5°C chilling injury, breakdown and
surface discoloration increased chilling
and pitting injury
Mango > 10 % Softening, off—flavor < 2 % discoloration of
(< 5 %) skin, grayish
flesh color, off-
flavor

 

35

 

Table 2.10: 02 thresholds causing injury for horticultural crops held at typical
storage temperatures [adapted from Beaudry (2000)]

 

 

 

 

 

 

 

 

 

 

 

02 (kPa) Commodities
0.5 or less Chopped green leaf, red leaf, Romaine and iceberg lettuce,
spinach, sliced pear, broccoli, mushroom
1 Broccoli florets, chopped butterhead lettuce, sliced apple,
brussels sprouts, cantaloupe, cucumber, crisphead lettuce,
onion bulbs, apricot, avocado, banana, cherimoya, atemoya,
sweet cherry, cranberry, grape, kiwifruit, Iitchi, nectarine,
peach, plum, rambutan, sweetsop
1'5 Most apples, most pears
2 Shredded and cut carrots, artichoke, cabbage, cauliflower,
celery, bell and chili pepper, sweet corn, tomato, blackberry,
durian, fig, mango, olive, papaya, pineapple, pomegranate,
raspberry, strawberry
2-5 Shredded cabbage, blueberry
3 Cubed or sliced cantaloupe, low permeability apples and
pears, grapefruit, persimmon
4 Sliced mushrooms
5 Green snap beans, lemon, lime, orange
10 Asparagus
14 Orange sections

 

 

 

 

36

Table 2.11: CO2 pressure thresholds causing injury for horticultural crops
(Beaudry 2000; Watkins 2000)

 

 

 

 

 

 

 

 

 

 

 

 

C02 (kPa) Commodity

2 Lettuce (crisphead), pear

3 Artichoke, tomato

5 Apple (most cultivars), apricot, cauliflower, cucumber, grape,
olive, orange, peach (clingstone), potato, pepper (bell)
Banana, bean (green snap), kiwi fruit
Papaya
Asparagus, brussels sprouts, cabbage, celery, grapefruit,

10 lemon, lime, mango, nectarine, peach (freestone),
persimmon, pineapple, sweet com

15 Avocado, broccoli, lychee, plum, pomegranate, sweetsop

20 Cantaloupe (muskmelon), durian, mushroom, rambutan

25 Blackberry, blueberry, fig, raspberry, strawberry

30 Cherimoya

 

 

 

Table 2.12: Recommended MA conditions for vegetables (Kader 1985; Aharoni

2004; Han 2005)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Modified Atmosphere
Commodity 133.23%; e % Oxygen % Carbon dioxide
9 (02) (C02)
Asparagus 0-5 20 (Air) 5-10
Bean, Snap 5-10 2-3 5-10
Bell pepper 8-12 3-5 0
Broccoli 0-5 1-2 5-1 0
Brussels sprouts 0-5 1-2 5-7
Cabbage 0-5 3-5 5-7
Cauliflower 0-5 2-5 2-5
Corn 0-5 2-4 1 0-20
Cucumber 8-12 3-5 0
Lettuce 0-5 2-5 0
Mushroom 0-5 20 (Air) 10-15
Spinach 0-5 20 (Air) 10-20
Tomatoes
Matu re-green 12-20 3-5 0
Partly ripe 8-12 3-5 0

 

 

37

2.5.2 Vacuum skin packaging (VSP)

Vacuum packaging is a packaging technique that can help to preserve the
freshness and extend the shelf life of products by removing the air inside the
package and then hermetically sealing them in a high barrier film. Vacuum
packaging has been commonly used for many dry foods and fresh meats since
the 1960s. In the US, vacuum packaging has been heavily used with poultry,
processed meats and cured cheeses. Around 1960, the Cryovac company
created barrier shrink film vacuum packaging to prolong the freshness of red
meat (Blakistone 1998).

Vacuum skin packaging (VSP) uses the same technique as vacuum
packaging but it applies a themoforrnable film to seal over the product against a
rigid backboard. This is widely used to prolong the storage shelf life of meats
(T ewari 2002). Vacuum packaging can also be used to package fresh produce.
However, vacuum skin packaging has not been widely used with fresh fruits and
vegetables. More research is needed in this area to ensure the quality of fresh
packed produce.

Vacuum packaging can help to retard the growth of aerobic
microorganisms, resulting in decreased spoilage. Vacuum packaging significantly
extended the shelf-life of sliced carrots at 4°C from 5 to 8 days and retarded
microbial growth compared with non-vacuum packed carrots (Buick and
Damoglou 2006). Generally, vacuum packaging helps to preserve product
appearance better than MAP (Beltran and others 2005). The effect of MAP and

vacuum packaging on the quality of chilled potato strips showed that potato strips

38

dipped in a 10% ascorbic acid solution and packed in a fiber tray lined with
Surlyn-PVdC-Surlyn under MAP (5% O2 and 10% CO2) at 5°C inhibited
enzymatic discoloration for 1 week while product under vacuum packaging had
minimum discoloration of chilled potato strips up to 2 weeks at the same storage
temperature (0' Beirne and Ballantyne 1987).

The gaseous atmosphere in vacuum packed fresh produce changes
during storage because it is impossible to remove all of the air from the package
(about 0.3 - 3% of air remains after sealing) and because of the respiration of
microorganisms and the fresh produce (lrtwange 2006). Applying high vacuum
pressure can cause bruising of fresh produce while low vacuum pressure may
not lower the 02 content in the initial headspace sufficiently (Blakistone 1998). A
suitable vacuum pressure must be used with fragile products such as fresh
produce.

2.5.3 Film

Plastics are . a commonly used packaging material for many food
packaging applications because of ease of forming, light weight, clarity, strength
and good heat sealing ability. Unlike other products, fresh-cut produce can still
breathe. Thus, respiration is a big concern when plastic films are used to protect
and extend the shelf life of fresh products.

There are 3 groups of films currently used in the fresh produce industry:
monolayer, laminated, and co-extruded films. Generally, the films used with MAP
are multilayer structures which are made from several layers of different types of

plastic using co-extrusion, lamination or coating technologies to achieve needed

39

properties. MAP laminated films are usually made from polyethylene (PE),
polypropylene (PP), polyamide (nylons), polyethylene terephthalate (PET),
polyvinyl chloride (PVC), polyvinylidene chloride (PVDC) and ethylene vinyl
alcohol (EVOH). For rigid and semi-rigid packaging, PP, PET, PVC and
expanded polystyrene are used to create tray containers for MAP (Blakistone
1998; Coles and others 2003) as illustrated in Table 2.13.

Table 2.13: Typical polymeric plastic materials for MAP containers (Coles and
others 2003)

 

 

Plastic material Application

UPVC/PE Thermoformed base tray
PET/PE Thermoformed base tray
XPP/EVOH/PE Thermoformed base tray
PS/EVOH/PE Thermoformed base tray
PET/EVOH/PE Thermoformed base tray
PVDC coated PP/PE Lidding film

PVDC coated PET/PE Lidding film

PA/PE Lidding film

PA/PE Flow warp film
PA/ionomer Flow warp film
PA/EVOH/PE Flow warp film

PET Pre-formed base tray
PP Pre-formed base tray
UPVC/PE Pre-formed base tray

 

The most important barrier characteristic that polymeric films need for
MAP and vacuum packaging is their permeability to oxygen, carbon dioxide, and
nitrogen or argon (Han 2005). Permeability is “the diffusion or molecular
exchange of gases, vapors or liquid permeates across a plastic material”
(Hernandez 1997). The rate of gas transmission through a perforated film is the
sum of gas diffusion through any perforations in the film and the gas permeation

through the polymeric film. In general, the total gas exchange through a

40

perforated film is much greater than the gas permeation through the plastic film

(Fishman and others 1996; Mir and Beaudry 2001).

Permeable plastic film has been developed for use with fresh produce to
control the gas exchange between the package head space and the external
environment (Zagory 1998). Plastic films help to moderate moisture loss, slow
down produce senescence and diminish product quality degradation (Schlimme
and Rooney 1994).

Using a suitable polymeric film is necessary for both MAP and vacuum
packaging to maintain quality of fresh-cut fruits and vegetables because of
product respiration rates. The choices of film permeability, thus, depend on the
respiration rates of the fresh produce (Kader 1989b; Paine and Paine 1992; Day
1993). Table 2.14 and 2.15 show the permeability of 02, CO2, N2 and water
vapor of different types of polymeric films for use with fresh produce at room
temperature. However, knowing the oxygen transmission rates at refrigerated
temperatures may provide more realistic permeability rate information for films
used in refrigerated storage conditions (Day 1993).

The permeation rates of the film rely on the partial pressure of the CO2
and O2 gases (Paine and Paine 1992; Zagory 1998). Semi-permeable polymeric
films are the most popular barriers used to create modified atmosphere (Talasila
and others 1995). Presently, most of the films used for MAP are suitable only for
the low and medium respiring commodities. Produce with high respiration rates
may need other film combinations and/or perforated films, to provide sufficient

flux of O2 and C02 (Kader 1989b; Exama and others 1993).

41

Microperforation of films to create small holes can be used to allow greater
gas movement across the package membrane (Mir and Beaudry 2001).
Microporous films have been developed by mixing polymer resin with inert
inorganic materials such as CaC03 and Si02 for the purpose of creating very high
gas transmission rates. Gas permeability can be controlled by adjusting the
particle size of the filler and degree of stretching obtained. In general, the
average pore size diameter is 0.14 — 1.4 pm (Mizutani and others 1993) for
methods such as FreshHold®, which was developed by Hercules (Hercules,
Wilmington, DE) (Zagory and Kader 1988; Roming and Nazir 2004).
Microperforated film has also been developed to achieve very high gas
transmission rates, using holes in the general range of 40-200 pm. For example,
P-plus, developed by Sidlaw (Sidlaw Packaging P-plus, Bristol, UK) and now
owned by Printpack (Printpack Inc, Atlanta, GA) has this technology (Zagory and
Kader1988; Roming and Nazir 2004).

Metallocene technology uses single-site catalyst (SSC) polymers that can
control molecular weight density and distribution. This technology helps to create
flexible plastics with very high oxygen transmission rates, low moisture vapor
transmission rates, clarity, strength and low seal initiation temperature. For
instance, polyolefin plastomer film (POP) created by Dow Chemical Co. and
Exxon Chemical Co., has high 02 and CO2 permeability that can facilitate the
packaging of fresh-cut produce (Young and Wooster 1996; Hernandez 1997;
Zagory 1998). Commercial films have also been developed to have higher gas

transmission, ethylene-vinyl acetate, low density polyethylene (Elvax, Dupont,

42

Wilimington, DE), styrene butadiene block copolymer films (K-Resin, Phillips
Chemical Co., Houston, TX) and ultra low density ethylene octene copolymer
films (Attane series, Dow Chemical Co., Midland, MI) (Roming and Nazir 2004).
Microperforated films (P-plus) have been shown to extend the storage
shelf life of various fresh fruits and vegetables such as asparagus, cherry
tomatoes, peppers, brussel sprouts, sweet corn, leeks, pears (Geeson 1988),
Iceberg lettuce (Ballantyne and others 1988) and mushroom (Lopez-Briones and
others 1993). Peeled white asparagus packed in P-plus 160 under MAP at 4°C
had longer shelf life than that packed in perforated PVC (Simon and others 2004).
This was shown to be the same for borage, a vegetable from the north of Spain,
packed in P-plus film and PVC (Gimenez and others 2003). Studies of shredded
carrots packed in oriented polypropylene (OPP), polyether block amide (DP) with
hydrophilic coating, Pebax (OSM) and P-plus bags at 3°C and 8°C also showed
that the P-plus film (002 permeability of 29 x 103 ml..m‘2.d".atm", 02 permeability
of 25 x 103 mL.m'2.d".atm") protected the product the best and retarded its
deterioration. These studies also found that the deterioration of the product was
related to the depletion of 02 rather than the increase of C02 inside the package
(Barry-Ryan and others 2000). The effect of film thickness on product shelf life
has been studied on honey peach fruit packed in a LDPE bag (thickness 15, 25,
40 um) and stored under a MAP composition of 6% O2 and 3% C02 at 2°C. The
results showed that the honey peach maintained its color and texture during 40
days of storage, and that the thickness of the LDPE film significantly affected the

product quality (Jianshen and others 2007).

43

Although a permeable film can help to extend product shelf life, either low,
medium or high-barrier films can contribute to problems associated with absence
of oxygen. This is because film properties tend to be more permeable to C02
than 02 (CO2 2 to 6 or 8 times higher than 02), resulting in diffusion of C02 gas
through the package wall faster than the diffusion of 02 gas into the package
(Zagory 1998; Mir and Beaudry 2001). When the oxygen level inside the package
approaches or reaches the zero level, anaerobic respiration occurs and causes
product deterioration. For instance, perforated polypropylene (PP) helped to
preserve the ripeness and nutritional value of MAP strawberries though it does
affect their color and flavor (Sanz and others 1999). Fresh-cut spinach packed in
monooriented polypropylene (OPP) and LDPE bags under MAP at 4°C and 90%
RH maintained weight but lost chlorophyll. An off-odor developed in the product
packed in OPP bags (Piagentini and others 2002).

Rigid plastic trays have been widely used for fresh-cut fruit and vegetables
because of their mechanical properties. However, the trays are impermeable
which reduces the surface area for gas exchange. The appropriate design of a
package can allow the produce to breathe. Therefore, the ratio of product weight
and headspace/surface area needs to be balanced (Zagory 1998). Some
research studies have shown that gas equilibrium inside the package, at low
temperature, will reach steady-state in about 2 to 3 weeks depending on the void
volume and the respiration rates of the products (Cameron and others 1995).

The development of permeable films continues. Recently, biodegradable

films have been used in MAP applications. Corn zein film was used as a

44

biodegradable material to extend the shelf life of fresh broccoli under MAP. The
research showed that product packed in zein films plasticized with oleic acid and
coated with tung oil, and stored under MAP at 5°C kept its freshness (color and
firmness) during 6 days of storage (Rakotonirainy and others 2001).

Table 2.14: Permeability of polymeric films for fresh produce (Zagory and Kader
1988; Aharoni 2004)

 

 

 

 

 

 

 

 

 

 

 

Permeability (cclmzlmillday at 1 atm)
Film Type
C02 02 C02;02 Ratio

Polyethylene

(low density) 7,700 - 77,000 3,900 - 13,000 2.0 - 5.9
Polyvinylchloride 4,263 - 8,138 620 - 2,248 3.6 - 6.9
Polypropylene 7,700 - 21,000 1,300 - 6,400 3.3 - 5.9
Polystyrene 10,000 - 26,000 2,600 - 7,700 3.4 - 3.8
Polyester 180 - 390 52 - 130 3.0 - 3.5
Saran 52 - 150 8 - 26 5.8 - 6.5

 

 

 

45

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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2.6 Storage and temperature

Temperature is another important factor that affects the metabolic rate of
fresh produce, and the success of MAP and vacuum packaging in extending the
shelf life and quality retention of horticultural products during storage. Too high a
temperature accelerates respiration, browning and microbial growth. Low
temperature in combination with MAP can successfully reduce the respiration
rate, ethylene production and pigment degradation and retard the growth of
microorganisms, all of which delay product spoilage (Kader 1989b; Ooraikul and
Stiles 1991; Heard 2002; Ternorio and others 2005).

Temperature affects not only the respiratory rate of fresh fruits and
vegetables but film permeability as well. When temperature increases above the
optimum level, the respiration rate of produce increases resulting in an increase
in C02 level and depletion of O2 (Exama and others 1993). With an increase in
temperature from 0°C to 15°C, there is a 4 to 6 fold increase in respiration of
most fruits and vegetables. When temperature increases, the respiration rate of
fresh produce increases at a rate of 2 or 3 times that of the increased
permeability of LDPE and 30 times the rate (LDPE) with perforations (1-mm
perforation in a 0.0025 mm (1 mil) thick LDPE film) (Beaudry and others 1992;
Cameron and others 1994; Lakakul 1999; Mir and Beaudry 2001). The
permeability of 02 and CO2 through LDPE film increases when the temperature
increases from 5°C to 35°C (Charles and others 2005). Since CO2 permeability
increases more than 02 permeability, when temperature increases, the

respiratory rate increases, resulting in increased C02 production and increased

47

O2 consumption. The decline in 02 levels inside the package causes
fermentation, resulting in off-odor development due to the production of ethanol
and acetaldehyde from anaerobic respiration (Phillips 1996).

Inappropriate temperature control can lead to the deterioration of fresh
produce and the potential for anaerobic microbial growth such as C. botulinum
which causes serious foodborne illness. Storage at 10°C or above is adequate
for most foodborne bacteria to grow and produce toxin on fresh cut vegetables.
While high temperatures accelerate the spoilage of fresh produce, low
temperature can sometimes cause chilling injury. Each produce species varies in
its sensitivity level to temperature, both in terms of respiration and chilling injury.
Fluctuating temperatures or changes in temperature should be avoided since
they cause moisture condensation inside the package, thus stimulating microbial
spoilage (Zagory and Kader 1988). To avoid temperature abusive conditions, it is
necessary to understand the specific requirements of fresh produce related to
temperature.

Fresh asparagus is a perishable vegetable which can be injured by
refrigeration. The deterioration of asparagus occurs rapidly when storage
temperature rises above 2°C (36°F) resulting in loss of sweetness, tenderness,
flavor and vitamin C. Asparagus is also damaged by chilling injury when the
temperature falls below 0°C (32°F). The recommended storage temperature for
asparagus is around 0 to 2°C (32-36°F) at 95 to 100% RH under controlled

atmosphere (CA) and MAP as shown in Tables 2.16 and 2.17 (ASHRAE 2002).

48

Storage temperature affects the shelf life of fresh-cut asparagus under
MAP and vacuum packaging. Fresh asparagus packaged under MAP at 2°C had
longer shelf life (26 days) than when stored at 10°C (14 days) or Non-MAP
storage at 2°C (9-12 days) (Villanueva and others 2005). Ternorio and others
(2004) also found that MAP at 2°C was successful in preserving asparagus shelf
life and its color including that from carotenoids and chlorophylls through 26-33
days. MAP at 10°C extended the product quality only 20 days, and only 14 days
at 2°C under non-MAP conditions. The use of MAP for fresh asparagus also

helps to reduce the loss of moisture and anthocyanins (Siomos and others 2000).

49

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Table 2.17: Optimal transit temperatures for various vegetables (USDA 1995;
UCANR 1997)

 

 

. . Suggested Highest
Commodities 'll?eer:|raet:aetu-lr;a(r1:; Thermostat Freezing Point
9 Setting (°F) (°F)
Artichokes 32 33 29.8
Asparagus 32 - 35 35 30.9
Lima beans 37 - 41 37 31.0
Snap beans 40 — 45 45 30.7
Beets (topped) 32 34 30.4
Broccoli 32 34 30.9
Brussels sprouts 32 34 30.6
Cabbage 32 34 30.4
Cantaloupes 36 - 41 37 29.8
Carrots 32 33 29.5
Cauliflower 32 34 30.6
Celery 32 34 31.1
Sweet corns 32 34 30.9
Cucumbers 50 - 55 50 31.1
Eggplant 46 - 54 50 30.6
Green leaves 32 34 -
Honeydew melon 45 — 50 45 30.4
Lettuce 32 34 31.6
Onions 32 - 39 35 30.6
Green onions 32 34 30.4
Green peas 32 34 30.9
Sweet peppers 45 - 50 46 30.7
Potatoes
Early crop 50 - 60 50 30.9
Late crop 39 — 50 40 30.9
Radishes 32 34 30.7
Spinach 32 34 31.5
Squash (summer) 41 - 50 41 31.1
Squash (winter) 50 — 55 50 30.5
Sweet potatoes 55 - 61 55 29.7
Tomatoes
Mature green 55 - 70 55 30.9
Pink 50 50 30.6
Waterrnelons 50 - 60 50 31.3

 

51

2.7 Sensory quality of fresh-cut asparagus

The appearance of fresh-cut fruits and vegetables is the most important
factor considered by consumers when buying produce. After harvest, the
physiology of fresh fruits and vegetables changes over time. Eventually the
product reaches its maturity stage and then senescence occurs due to
respiration resulting in changes in appearance, odor, color, flavor and texture
which cause the loss of the fresh-like quality. In addition, cutting results in broken
cells which also hasten the degradation of fresh products. Although MAP is
widely used to increase the shelf life of fresh-cut products, undesirable changes
such as discoloration, off-odor and off-flavors can occur during storage and
reduce the product quality (Kader 1986).

Aroma, color and texture can be used to represent the freshness of fresh
produce. Moisture loss, mechanical damage and microbial spoilage are involved
in the degradation of fresh-cut produce (Piagentini and others 2002). Most fresh-
cut produce research has focused on browning, discoloration, flavor, texture and
microbial growth and their effect on product shelf life. Analytical analysis has
been used to measure color, aroma and texture of the fresh fruits and vegetables.
It, however, is able to determine only visual or chemical properties. Thus, use of
human senses can help to judge the product quality more precisely (Abbott and
others 1997).

Sensory analysis is a scientific method which uses the human senses
(sight, smell, taste, touch or hearing) to efficiently assess product quality and

shelf life (ASTM 1992). Assessing product sensory characteristics requires

52

different tests depending on the objective, such as development of a new product,
product matching, improvement and cost reduction, raw material change and
storage stability (Hutchings 1994). Consumer tests are the most effective test
technique for product preference and acceptance, and generally require 50 - 100
panelists. A typical 9-point hedonic scale is often used, while discrimination tests
can be used to detect the difference in similar products. Descriptive analysis
methods measure both the qualitative and quantitative sensory aspects of
products by using a trained panel (recommended minimum number of panelists
is 5) (Meilgaard and others 1991; Baldwin 2002). Sensory evaluation cannot be
fully unbiased; however, bias can be minimized by use of a well designed
experiment and scoring system, and by enhanced training of the panelists
(Hutchings 1994).

For ready-to-eat products, fresh produce is cut and packed into a package.
The proper selection of the plastic film as a packaging material is crucial to the
shelf life of the product. The permeability of the film can help to maintain the
quality of the fresh produce by lessening the degradation of chlorophyll and other
pigments, and to reduce browning and microbial growth by creating and
maintaining an atmosphere inside the package during storage (Cartaxo and
others 1997; Watada 1997; Senesi and others 1999; Bett 2002). Since the
product is packed, consumers are able to evaluate the product quality only by its
appearance and hence it is the key factor in making a purchase decision. Most

research on product quality of fresh-cut produce is centered on the visual and

53

quality appearance (Beaulieu and Baldwin 2002) of the product and color is the
most critical feature of its visual appearance.

Fruits and vegetables have their own unique color. The progressive color
of some fresh fruits and vegetables changes from green to yellow (cucumbers,
broccoli, asparagus and bananas), while some change from green to red or
orange (tomatoes, strawberries, cherries and oranges). These color changes
demonstrate the ripeness and eventual degradation of the produce. Like other
green vegetables, the green color of the asparagus stalk is representative of its
freshness color due to chlorophyll. Chlorophyll synthesis involves the
transformation of protochlorophyllide into chlorophyllide and later to chlorophyll.
Most likely, the degradation of chlorophyll is caused by chlorophyllase resulting in
the development of chlorophyllide which can be converted into yellow and brown
compounds and then into colorless compounds (Schouten and Van Kooten
2000). Browning, caused by oxidation of phenols and catalyzed by polyphenol
oxidase enzymes, can produce off-flavor. It can also result in loss of quality in
some fresh-cut products such as potatoes, avocado, lettuce, and apples
(Whitaker 1995; Bett 2002).

Aroma and flavor can be characterized as components of the sensory
quality of fresh produce. They are critical to the consumer repurchase (Beaulieu
and Baldwin 2002). Unlike other food products, fresh-cut fruits and vegetables
still continue to respire after harvest. With one purpose of MAP being shelf life
extension, control of the 02/002 inside the package is critical since 02 is

consumed during respiration while C02 elevates. The concentration of 02 and

54

CO; determines the metabolic rate of the plant tissue. An 02 concentration less
than 2% or C02 concentration more than 5% may change the metabolic
reactions within the living tissue from aerobic to anaerobic respiration, causing
fermentation that creates undesirable odors and flavors and thereby reduces the
shelf life of the product (Powrie and Skura 1991; Farber and others 2003; Saltveit
2003). When 02 levels in MAP decrease below the tolerance level of fresh
produce such as in fresh-cut green asparagus spears (Baxter and Waters 1991),
potatoes (Beltran and others 2005) and broccoli (Dan and others 1997), off-flavor
develops due to anaerobic respiration. To assess the aroma and flavor sensory
qualities of fresh fruits and vegetables, raw, fermented and rotten odor/flavor
notes are used as attributes as shown in Table 2.18 (Bett 2002).

Table 2.18: Descriptors with definitions and references for odor/flavor of fresh
fruits and vegetables (Bett 2002)

 

 

 

 

 

 

 

 

Airgaéizzor Description Reference

Raw Aroma associated with Fresh fruit or vegetable
unprocessed and/or
uncooked product

Fermented Aroma associated with Fermented apple juice or
fermented fruits or WONF 3RA654 (McCormick)
vegetables

Deteriorated/ rotten Aroma associated with Rotten fruit or vegetables
rotten, deteriorated, (specific)
decayed fruit/material

 

Texture is an important factor in characterizing the freshness of fresh fruits
and vegetables. Physical characteristics, including the structural elements, can
be assessed by the look of the product, by sensation of touch to the hand and/or
in the mouth (Bourne 1982; Abbott 2004). Generally, consumers perceive the

texture of fresh produce by squeezing the product (Voisey and Crete 1973;

55

Rosenthal 1999). The touch/feel helps consumers to determine its actual product
quality. Products soften because of pectolytic activity and cellulose breakdown,
resulting in moisture loss, wilt and wrinkled appearance (Lieberman 1981). The
structural, physiological and biochemical characteristics of fresh fruits and
vegetables and their varying stages of development are used to evaluate textural
characteristics. Many terms are used to describe the sensory texture of fruits
and vegetables such as hard, firm, soft, crunchy, crisp, limp, mealy, tough,
leathery, melting, gritty, stringy, dry and juicy (Abbott 2004). Different fruits and
vegetables are comprised of different tissues which differ in strength and
biological properties. Hence, different product sections need to be considered
individually when measuring the texture. For example, crispness/toughness is a
principal attribute of asparagus caused by fiber content and fiber lignification
(Lipton 1990). The crispness/toughness of asparagus spears stored under MAP
in semi-permeable film at 6°C has been shown to degrade faster than the color
and hence can be used as a measurable parameter to evaluate the sensory
quality (Albanesea and others 2007).
2.8 Microbiological safety of fresh-cut asparagus

Microbial spoilage affects product quality and shelf life. The growth of
microorganisms leads to deterioration, and can lead to a principle food safety
concern. Raw fruits and vegetables can be contaminated with microorganisms in
the field, through processing, and packing and in transportation, all of which can
lead to human foodborne disease. In the fresh-cut produce industry, bacterial

total count and coliform numbers can be used as indicators of a product’s

56

sanitation and quality (Heard 2002) even though some researchers recommend
not to use coliform numbers to indicate contamination with fecal pathogens
(Beuchat 1998; Nguyen-The and Carlin 2000).

Unlike some food processing techniques such as freezing and canning,
fresh-cut products are processed without heat treatment to maintain the
freshness of the product (Heard 2002). In most cases, the type of pathogen and
spoilage microorganisms found on fresh-cut produce and raw crops are similar
(Nguyen-The and Carlin 2000). Contamination of fresh-cut products may occur in
the field and/or in processing. Washing fruits and vegetables after cutting or
trimming helps to reduce the pathogen and spoilage load (Sinigaglia 1999).
However, only 1 log reduction in microbial numbers is achieved by washing with
water (Nguyen-The and Carlin 1994). Washing fresh fruits and vegetables with
water and the addition of a disinfectant such as chlorine can help to reduce the
microbial load further (1-2 log reduction) (Cherry 1999; Parish and others 2003).

MAP and vacuum packaging techniques can help to extend the shelf life
of fresh produce, but can also allow the development of pathogens even when
the product is stored at low temperature due to long storage and/or inappropriate
package headspace gas composition (Brackett 2000; FDA 2001). Thus,
microbiological safety is a serious concern for the fresh-cut produce industry
using either MAP or vacuum packaging.

Much research has been done on L. monocytogenes as a contaminant of
fresh produce stored under MAP. Listeria monocytogenes is a critical foodborne

bacterial pathogen, and can grow and survive at refrigeration temperature. In

57

1989, a zero tolerance policy was enforced for L. monocytogenes in food by the
US. Department of Agriculture and US. Food and Drug Adminstration (Altekruse
and others 1997). L. monocytogenes is a concern as a pathogenic contaminate
in ready-to-eat foods such coleslaw, milk (after pasteurization) and MAP produce
(Schuchat and others 1991; NACMCF 1999). It has been reported that L.
monocytogenes inoculated on fresh broccoli, asparagus and cauliflower packed
under MAP composed of 3%CO2, 18 % O2 and 79% N2 at 10°C for 10 days was
unaffected (Berrang and others 1989). However, the population of L.
monocytogenes on trimmed, fresh green asparagus stored under MAP at 2°C
and 4°C, and then increased to 8°C at the rate of 0.038°C/hour (Castillejo
Rodriguez 2000).

Aeromonas hydrophila has been found on a variety of foods and there is
concern that it is a foodborne pathogen in fresh-cut fruits and vegetables. Under
MAP (11-18% 02, 3-10% CO2 and 97% N2), the shelf life of fresh broccoli,
asparagus and cauliflower was extended from 8-21 days at 4°C and 15°C. CO2
levels of more than 50% have been reported to inhibit the growth of L.
monocytogenes and A. hydrophila. However, CO2 levels this high can injure
products (Bennik and others 1995).

Microbial growth on fresh asparagus in vacuum packaging has been
reported. During a 21-day storage period at 2°C 80% RH, the total
Enterobacteriaceae counts (2.5 x 102 CFU/g), and yeast and mold (10 CFUIg) on
asparagus packed in Poliskin-X bags under vacuum packaging was lower than

the Enterobacten’aceae counts (7.3 x 104 CFU/g)- and yeast and mold (2.3 x 104

58

CFU/g) counts on asparagus packed in low density polyethylene bags under
MAP. Anaerobic psychrotrophs were found in both vacuum packaged (basically
lactic acid bacteria of the Lactobacillus genus) and MAP (principally Coryneforrns,
Pseudomonas and Acinetobacter anitratus) (Osuna and others 1995).

There is potential growth of Clostridium botulinum on fresh-cut produce
under MAP and vacuum packaging since C. botulinum can grow in an anaerobic
environment (Zagory 1995). Several research studies have found that fresh
products were grossly spoiled before the botulinal toxin produced by C.
botulinum was detected in the product. For example, shredded carrots and green
beans (Hao and others 1998), romaine lettuce and shredded cabbage (Petran
and others 1995), and cantaloupe and honeydew (Larson and Johnson 1999)
have all shown this result. However, research with onions and butternut squash
packed under MAP at 5°C (41°F) for 21 days and 25°C (77°F) for 6 days showed
that both nonproteolytic and proteolytic strains of C. botulinum appeared when
toxin was detected (Austin and others 1998). Thus, the production of toxin by C.
botulinum varies with the vegetable (FDA 2001). It has been claimed that the
overall occurrence of C. botulinum spores in pre-cut fresh vegetables under MAP
at 4°C (39.2”F) at retail suppliers in the US. is low, only 0.36% (1 of 337) (Lilly
and others 1996). This pathogen is difficult to grow and cannot produce toxin in
the product stored at a temperature below 12°C, pH below 4.6, a water activity
below 0.95 and NaCl concentrations above 10% (Lund and Peck 2000).

Escherichia coli (E .coli) O157:H7 is another serious foodborne pathogen

which causes food-poisoning. E. coli O157:H7 can contaminate fresh fruits and

59

vegetables during harvesting, processing and packing (FDA 2001). It has been
found that the CO2 concentration of shredded iceberg lettuce in MAP using 4
different gas mixture ratios (O2:CO2:N2): 0:10:90, 3:0:97, 5:30:65, and 20:0:80,
and stored at 13°C and 22°C had no significant effect on the growth of E. coli
O157:H7 at both temperatures (Diaz and Hotchkiss 1996). It was also found that
shredded lettuce, sliced cucumber, and shredded carrot packed under MAP
containing 3% 02, 0.3% CO2 and 97% N2 at 5, 12, and 21°C had no effect on the
development of E. coli, psychrotrophs, or mesophiles. The reduction in pH of the
vegetables allows the growth of E. coli O157:H7 and other microorganisms

(Abdul-Raouf and others 1993).

60

2.9 BIBLIOGRAPHY

Abbott JA. 2004. Textual qaulity assenssment for fresh fruits and vegetables. In:
Shahidi F, Spanier, A.M., Ho, C., Braggins, T., editor. Quality of fresh and
processed food. New York: Kluwer Academic/Plenum Publishers. p 265-
79.

Abbott JA, Lu R, Upchurch BL, Stroshine RL. 1997. Technologies for
nondestructive quality evaluation of fruits and vegetables. Hort Rev
20(1):120.

Abdul-Raouf UM, Beuchat LR, Ammar MS. 1993. Survival and growth of
Escherichia coli O157:H7 on salad vegetables. Applied and Environmental
Microbiology 59(7 ):1999-2006.

Aharoni N. 2004. Packaging, Modified Atmosphere (MA) and Controlled
Atmosphere (CA)-Principle and applications. International research and
development course on postharvest biology and tecnology The Volcani
Center, Israel.

Ahvenainen R. 1996. New approaches in improving the shelf life of minimally
processed fruit and vegetables. Trends in Food Science and Technology
7:179 87.

Albanesea D, Russoa L, Cinquantab L, Brasielloa A, Di Matteo M. 2007. Physical
and chemical changes in minimally processed green asparagus during
cold-storage. Food Chemistry 101 (1)2274-80.

Allende A, Tomas-Barberan FA, Gil MI. 2006. Minimal processing for healthy
traditional foods. Trends in Food Science & Technology 17(9):513-9.

Altekruse SF, Cohen ML, Swerdlow DL. 1997. Emerging Foodborne Diseases.
Emerging Infectious Diseases 3(3):285-93.

Amanatidou A, Smid EJ, Gorris LGM. 1999. Effect of elevated oxygen and
carbon dioxide on the surface growth of vegetable-associated micro-
organisms. Journal of Applied microbiology 86(3):429-38.

ASHRAE. 2002. ASHRAE refrigeration handbook. Atlanta, GA: American Society
of Heating, Refrigerating, and Air-Conditioning Engineers. p 23.1 -.16.

ASTM. 1992. MNL 14. The Role of Sensory Analysis in Quality Control

Austin JW, Dodds KL, Blanchfield B, Farber JM. 1998. Growth and toxin
production by Clostridium botulinum on inoculated fresh-cut packaged
vegetables. Journal of Food Prot 61(3 ):324-8.

61

Baldwin EA. 2002. Fruit and Vegetable Flavor. In: Gross KC, Wang, C.Y., Salveit,
M.E., editor. The commercial storage of fruits, vegetables, and florist and
nursery stocks. Washington DC: Agricultural Research Service.

Ballantyne A, Stark R, Selman JD. 1988. Modified atmosphere packaging of
shredded lettuce. International Journal of Food Science & Technology
23(3):267-74.

Barry-Ryan C, Pacussi JM, O'Beirne D. 2000. Quality of shredded crarots as
affected by packaging film and storage temperature. Journal of Food
science 65(4):726-30.

Baxter L, Waters L. 1991. Quality changes in asparagus spears in a flow through
CA system or in consumer packages. HortScience 26:399-402.

Beaudry RM. 2000. Responses of horticultural commodities to low oxygen: limits
to the expanded use of modified atmosphere packaging. Hort Technology
10:491-500.

Beaudry RM, Cameron AC, Shirazi A, Dostal-Lange DL. 1992. Modified-
atmosphere packaging of blueberry fruit: Effect of temperautre on package
02 and COZ. Amer Soc Hort Sci 117:436-11.

Beaulieu JC, Baldwin EA. 2002. Flavor and aroma of fresh-cut fruits and
vegetables. In: Lamikanra O, editor. Fresh-cut fruits and vegetables:
Science, Technology, and Market: Boca Raton: CRC Press. p 392-415.

Behe BK. 2006. Conjoint analysis reveals consumers prefer long, thin asparagus
spears. Hortscience 41 (5): 1 259-62.

Beltran D, Selma MV, Tudela JA, Gil MI. 2005. Effect of different sanitizers on
microbial and sensory quality of fresh-cut potato strips stored under
modified atmosphere or vacuum packaging. Postharvest Biology and
Technology 37(1):37-46.

Bennik MHJ, Smid EJ, Rombouts FM, Gorris LGM. 1995. Growth of
psychotrophic foodborne pathogens in a solid surface model system under
the influence of carbon dioxide and oxygen. Food Microbiology 12:509-19.

Benson BL. 2005 Update of the world’s asparagus production areas, spear
utilization, yields and production periods.

Berrang ME, Brackett RE, Beuchat LR. 1989. Growth of Listeria monocytogenes
on fresh vegetables stored under controlled atmosphere Food Prot
52(10):702-5.

62

Bett KL. 2002. Evaluating sensory quality of fresh-cut fruits and vegetables In:
Lamikanra O, editor. Fresh-cut fruits and vegetables: Science, Technology
and Market: Boca Raton: CRC Press. p 427-38.

Betz Laboratories Inc. 1980. Betz Handbook: Handbook of industrial water
conditioning. 8 ed. Trevose, PA: Betz. 24-9 p.

Beuchat LR. 1998. Surface decontamination of fruits and vegetables eaten raw:
a review. Food Safety Uni World Health Organization. p 1-42.

Blakistone BA. 1998. Principles and applications of modified atmosphere
packaging of food. 2 ed: Blackie Academic & Professional, an imprint of
Thomson Science. 1-38, 123-34 p.

Bourne MC. 1982. Food texture and viscosity; Concept and measurement. New
York: Academic Press.

Brackett RE. 1992 Shelf stability and safety of fresh produce as influenced by
sanitation and disinfection. Journal of Food Protection 55 (10 ):808-14.

Brackett RE. 2000. Safe Handling of Fruits and Vegetables In: Farber JM, editor.
Safe handling of foods. New York: Marcel Dekker. p 79-104.

Brown W. 1922. On the germination and growth of fungi at various temperature
and in various concentrations of oxygen and carbon dioxide. . Annals of
Botany 36:257-83.

Buck JW, Walcott RR, Beuchat LR. 2003. Recent trenes in microbiological safety
of fruits and vegetables. Plant Health Progress.

Buick RK, Damoglou AP. 2006. The effect of vacuum packaging on the microbial
spoilage and shelf-life of ready-to-use sliced carrots. Journal of the
Science of Food and Agriculture 38(2):167-75.

Calvin L, Cook R, Denbaly M, Dimitri C, Glaser L, Handy C, Jekanowski M,
Kaufman P, Krissoff B, Thompson G, Thornsbury S. 2001. US. Fresh
Fruit and Vegetable Marketing: Emerging Trade Practices, Trends, and
Issues. US. Department of Agriculture.

Cameron AC, Beaudry RM, Banks NH, Yelanich MN. 1994. Modified Atmosphere
Packaging of blueberr fruit: modeling respiration and packge oxygen
partial pressures as a function of temperature. Amer Soc Hort Sci
119:534-9.

Cameron AC, Talasila PC, Joles DW. 1995. Predicting film permeability needs
for modified atmosphere packaging of lightly processed fruits and
vegetables. HortScience 30(1):25-34.

63

Cartaxo CBC, Sargent SA, Huber DJ, Lin CM. 1997. Controlled atmosphere
storage suppresses microbial growth on fresh-cut watermelon.
Proceedings of Florida State Horticultural Society 110:252-7.

Castillejo Rodriguez AM, Barco-Alcala, E., Garcia-Gimeno, R.M., Zurera-Cosano,
G. 2000. Growth modelling of Listeria monocytogenes in packaged fresh
green asparagus. Food Microbiology 17(421-427).

Charles F, Sanchez J, Gontard N. 2005. Modeling of active modified atmosphere
packaging of endives exposed to several postharvest temperatures.
Journal of food science 70(8):E443-9.

Cherry JP. 1999. Improving the safety of fresh produce wtih antimicrobials. Food
Technology 53(1 1):54-9.

Coles R, McDowell D, Kinivan MJ. 2003. Food packaging technology. Giles GA,
editor. GlaxoSmithKine, London: Blackwell Publishing Ltd. 303-39 p.

Dan KS, Nagata TM, Yamashita l. 1997. Formation of volatile sulfur compounds
inbroccoli stored under anaerobic condition. . Journal of Japan Soc Hort
Sci 652867-75.

Day BPF. 1993. Fruit and vegetables. In: Parry RT, editor. Principles and
applications of MAP of foods. New York, USA: Blackie Academic and
Professional. p 114-33.

Diaz C, Hotchkiss JH. 1996. Comparative growth of Escherichia coli O157:H7,
spoilage organisms and shelf-life of shredded iceberg lettuce stored under
modified atmospheres. Journal of Science Food Agric 70:433-8.

Dilley DR. 1990. Historical aspects and perspectives of controlled atmosphere
storage. lnzFood Preservation by Modified Atmospheres. Caldron MaB-G,
R., editor. Boston, MA.: CRC Press, Inc. 187-96 p.

Exama A, Arul J, Lencki RW, Lee LZ, Toupin C. 1993. Suitability of plastic films
for modified atmosphere packaging of fruits and vegetables. Journal of
Food Sci 58(6):1365-70.

Fallik E, Aharoni Y. 2004. Postharvest physiology. Pathology and Handling of
fresh produce.

FAO. 1989. Prevention of post-harvest food losses fruits, vegetables and root
crops 3 training manual. Chapter 4: Perishable and product loss-
Respiration: Food and Agriculture Organization of The United Nations,
Rome.

64

Farber JN, Harris LJ, Parish ME, Beuchat, L.R. S, T.V., Gomey JR, Garrett EH,
Busta FF. 2003. Microbiological safety of controlled and modified
atmosphere packaging of fresh and fresh-cut produce. Comprehensive
reviews in food science and food safety 22142-60.

FDA. 2001. Microbiological safety of controlled and modified atmosphere
packaging of fresh and fresh-cut produce, Chapter 4. Analysis and
evaluation of preventive control measures for the control and
reduction/elimination of microbial hazard on fresh and fresh-cut produce
USDA. p 1-53.

FDA/CFSAN. 2004. Evaluation and definition of potentially hazardous foods.
Chapter 4 In: Analysis of Microbial Hazards Related to Time/Temperature
Control of Foods for Safety.

Fishman S, Rodov V, Ben-Yehosha S. 1996. Mathematical model for perforation
effect on oxygen and water vapor dynamics in modified-atmosphere
packages. Journal of Food Science 612956-61.

Floros JD. 1990. Controlled and modified atmospheres in food-packaging and
storage. Chem Eng Progress 86:25-32.

Forsythe SJ, Hayes PR. 1998. Food Hygiene, Microbiology and HACCP. 3 ed.
Gaithersburg, MD: Aspen. 120-2 p.

Garrett H. 2002. Fresh-cut produce: tracks and trends. In: Lamikanra O, editor.
Fresh-cut fruits and vegetables: science, technology, and market. Boca
Raton: CRC Press. p 1-10.

Geeson JD. 1988. Modified atmosphere packaging of fruits and vegetables.
International Society for Horticultural Science (lSHS):143-7.

Gimenez M, Olarte C, Sanz S, Lomas C, Echavarri JF, Ayala F. 2003. Influence
of packaging films on the sensory and microbiological evoluation of
minimally processed borage (Borrago officinalis). Journal of Food Science
68(3):1051-8.

Gonzalez-Meler MA, Ribas-Carbo M, Siedow JN, Drake BG. 1996. Direct
Inhibition of plant mitochondrial respiration by elevated CO2. Plant
Physiology 1 12(3): 1 349-55.

Guzewich JJ, Salsbury PA. 2001 FDA’s role in traceback investigations for
produce: Improving response to foodborne illness outbreaks. Food Safety
magazine, December 2000 - January 2001:1-3.

Han HJ. 2005. Innovations in food packaging. San Diago, California, USA.:
Elsevier Academic Press. 159-72 p.

65

Hao YY, Brackertt RE, Beuchat LR, Doyle MP. 1998. Microbiological quality and
the inability of proteolytic Clostridium botulinum to produce toxin in film-
packed fresh-cut cabbage and lettuce. Journal of Food Prot 61 :1 148-53.

Hausbeck MK, Kalchik T, Myers N, DeKryger P, Steiner R, Greiner S, Kokx G,
Oomen K, Oomen T, \frnke S, Walsworth D, Winkle R. 2002. Green
project: Feasibility study for developing new markets for Michigan
asparagus.

Heard GM. 2002. Microbiology of fresh-cut produce. In: Lamikanra O, editor.
Fresh-cut fruit and vegetable: Science, Technology and market: Boca
Raton: CRC Press. p 188-226.

Hernandez RJ. 1997. Food packaging materials barrier properties and selection.
In: Valentas KJ, Rotstein, E., Singh, R.P., editor. Handbook of food
engineering practice. Boca Raton, FL.: CRC Press. p 293-395.

Hexamer FM. 1901. Asparagus, its culture for home use and for market; a
practical treatise on the planting, cultivation, harvesting, marketing, and
preserving of asparagus, with notes on its history and botany. New York:
Orange Judd Company. 1-4, 83-99 p.

Hutchings JB. 1994. Food color and appearance. 1 ed. Glasgow G64 2N2, UK:
Blackie Academic & Professional. 104-9, 42-69 p.

IFPA. 2003. Flexible packaging material basics. In: Gorny JR, editor. Packaging
design for fresh-cut produce: International Fresh-cut Produce Association.
p 1-3.

lrtwange SV. 2006. Application of modified atmosphere packaging and related
technology in postharvest handlng of fresh fruits and vegetables. . Journal
of the CIGR (E-Journal) 8(4):1-12.

Jianshen A, Zhang M, Zhan Z. 2007. Effect of packaging film on the quality of
Chaoyang honey peach fruit in modified atmosphere packags. Packaging
Technology and Science 20(1):71-6.

Kader A.A. Modified and controlled atmosphere storage of troical fruits; 1993.;
Procedding of an International Conference, Chiang Mai, Thailand. 19-23
July 1993. p 239-49.

Kader AA. 1985. Modified atmosphere and low—pressure systems during
transport and storage. In: Kader AA, Kasmire, R.F., Mitchell, F.G., Reid,
M.S., Sommer, W.F., Thompson, J.E., editor. Postharvest Technology of
Horticultural Crops Special Publ. 3311. University of California, Davis, CA.
p 58-67.

66

Kader AA. 1986. Biochemical and physiological basis for effects of controlled and
modified atmospheres on fruits and vegetables. Food Technology
40(5):99-104.

Kader AA. A summary of CA requirements and recommendations for fruit other
than pome fruits; 1989a; Wenatchee, Washing ton USA.14-16 June 1989.
Other Commodities and Storage Recommendations. p 303-28.

Kader AA. Postharvest biology and technology; 1992 University of California.

Kader AA. Modified and controlled atmosphere storage of tropical fruits.; 1993;
Proceeding of an lntemational Conference, Chiang Mai, Thailand. 19-23
July 1993. p 239-49.

Kader AA, Ben-Yehoshua S. 2000. Effects of superatmospheric oxygen levels on
postharvest physiology and quality of fresh fruits and vegetables.
Postharvest Biology and Technology 20:1-13.

Kader AA, Zagory, D., Kerbel, E.L. 1989b. Modified atmosphere packaging of
fruits and vegetables. CRC Crit Rev Food Sci 28(1):1-30.

Lakakul R, Beaudry, R.M., amd Hernamdez, R.J. . 1999. Modeling respiration of
apple slices in modifed atmosphere packages. Journal of food science
64:105-10.

Larson AE, Johnson EA. 1999. Evaluation of botulinal toxin production in
packaged fresh-cut cantaloupe and honeydew melons. Journal of Food
Prot 62(8):948-52.

Lieberman M. 1981. Post-harvest physiology and crop preservation. New York:
NATO Scientific Affairs Division [by] Plenum Press. 99-119 p.

Lilly T, Solomon HM, Rhodehamel EL. 1996. Incidence of Clostridium botulinum
in vegetables packaged under vacuum or modified atmospheres. Journal
of Food Protection 59:59-61.

Lipton WJ. 1990. Postharvest biology of fresh asparagus. Hort Rev 12269-155.

Lopez-Briones G, Varoquaux P, Bureau G, Pascat B. 1993. Modified atmosphere
packaging of common mushroom. lntemational journal of food science &
technology 28(1):57-68.

Lund BM, Peck MW. 2000. Clostridium botulinum. In: Lund BM, Baird-Parker,
T.C., Gould, G.W. , editor. The microbiological safety and quality of food.
Gaithersburg, MD: Aspen. p 1057-109.

Luo Y, Suslow T, Cantwell M. 2006. Asparagus. United States Department of
Agriculture-Agricultural Research Service (USDA-ARS).

67

MAAB. 2005. Welcome to Asparagus online. Michigan Asparagus Advisory
Board.

MDA. 2007. Asparagus. Michigan Department of Agriculture.

Meilgaard M, Civille GV, Carr BT. 1991. Sensory evaluation techniques. 2 ed.
Boca Raton, FL.: CRC Press, Inc. 187-211 p.

Michigan State University-Workshop summary. 2000. Pest management in the
future: A strategic plan for the Michigan asparagus industry.

Mir N, Beaudry RM. 2001. Handbook 66: Modified Atmosphere Packaging.
United States Department of Agriculture Publication (submitted).

Mizutani Y, Nakamura S, Kaneko S, Okamura K. 1993. Microporous
polypropylene sheets. Ind Eng Chem Res 32.

Moleyar V, Narasimham P. 1994. Modified atmosphere packaging of vegetables:
an appraisal. Journal of Food Sci Technol 31(4):267-78.

NACMCF. 1999. Microbiological safety evaluations and recommendations on
fresh produce. Food Control, National Adcisory Committee on
Microbiological Criteria for Foods 10:1 17-43.

Nguyen-The C, Carlin F. 1994. The microbiology of minimally processed fresh
fruits and vegetables. Critical Reviews in Food Science and Nutrition
34(4):371-401.

Nguyen-The C, Carlin F. 2000. Fresh and processed vegetables. In: Lund BM,
Baird-Parker, T.C., Gould, G.W., editor. The microbiological safety and
quality of food Maryland: Aspen Publishers, Inc.

0' Beirne D, Ballantyne A. 1987. Some effects of modified atmosphere
packaging and vacuum packaging in combination with antioxidants on
quality and storage life of chilled potato strips. International Journal of
Food Science & Technology 22(5):515-23.

Ooraikul B, Stiles ME. 1991. Modified Atmosphere Packaging of Food. Watson
DH, editor. New York: Ellis Harwood Limited. 147,170-227 p.

Osuna JJ, Zurera G, Garcia RM. 1995. Microbial growth in packaged fresh
asparagus. Journal of Food Quality 18 203-14.

Paine FA, Paine HY. 1992. A handbook of food packaging. 2 ed: Blackie
Academic & Professional. 242-5 p.

68

Papadopoulou PP, Siomos, A.S., Dogras, CC. 2001. Metabolism of etiolated
and green asparagus before and after harvest. Journal of horticultural
science and biotechnology 76(4):497-500.

Parish ME, Beuchat LR, Suslow TVH, L.J., Garrett EH, Farber JN, Busta FF.
2003. Method to reduce/eliminate pathogens from fresh and fresh-cut
produce. Comprehensive reviews in food science and food safety. p 161-
73.

Park CM, Beuchat, L.R. . 1999. Evaluation of sanitizers for killing Escherichia coli
O157:H7, Salmonella and naturally occurring microorganisms on
cantaloupes, honeydew melons and asparagus. Dairy Food Environ Sanit
19:842-7.

Peirce LC. 1987. Vegetables: Characteristics, production, and marketing. New
York: Wiley. 173-83 p.

Petran RL, Sperber WH, Davis AR. 1995. Clostridium botulinum toxin formation
in romaine lettuce and shredded cabbage: effect of storage and prackging
condition. Journal of Food Prot 58:624-7.

Phillips CA. 1996. Review: Modified atmosphere packaging and its effects on the
microbiological quality and safety of produce. International Journal of Food
Science and Technology 31 :463-79.

Piagentini AM, Guemes DR, Pirovani ME. 2002. Sensory Characteristics of
fresh-cut spinach preserved by combined factors methodology. Journal of
Food Science 67(4):1544-8.

Pirovani M, Piagentini A, Guemes D, Arkwright S. 2004. Reduction of chlorine
concentration and microbial load during washing-disinfection of shredded
lettuce Journal of Food Science 39 341-7.

Plotto A, Narciso JA. 2006. Guidelines and acceptable postharvest practices for
organically grown produce. HortScience 41 (2)287 - 91.

Powrie WD, Skura BJ. 1991. Modified atmosphere packaging of fruits and
vegetables. In: Ooraikul B, Stiles, M.E., editor. Modified atmosphere
packaging of food. New York, USA: Ellis Horwood Limited. p 169-245.

Rakotonirainy AM, Wang Q, Padua GW. 2001. Evaluation of zein films as
modified atmosphere packaging for fresh broccoli Journal of Food Science
66 (8 ):1108-11.

Ritenour MA, Sargent SA, Bartz JA. 2002. Chlorine Use In Produce Packing
Lines

69

Ritenour MA, Sargent SA, Brecht JK. 2000. Sanitizers for vegetable
packinghouse recirculated water The Vegetarian

Roming WR, Nazir M. 2004. Packaing technology for fresh produce. American
Society for Plasticulture.

Rosenthal AJ. 1999. Food texture measurement and perception. Gaithersburg,
Maryland, USA: Aspen Publishers, Inc.

Saltveit ME. A summary of requirements and recommendations for the controlled
and modified atmosphere sotrage of harvested vegetables; 1989;
Wenatchee, Washington, USA. Other Commodities and Storage
Recommendations. p 329-52.

Saltveit ME. 2003. Fresh-cut vegetables. In: Bartz JA, Brecht, J.K., editor.
Postharvest physiology and pathology of vegetables. 2 ed. New York, NY.:
Marcel Dekker, Inc. p 691-709.

Sanz C, Perez AG, Olias R, Olias JM. 1999. Quality of strawberries packed with
perforated polypropylene. Journal of Food Science 64(4):748-52.

Sapers GM. 2001. Efficacy of washing and sanitizing methods for disinfection of
fresh fruit and vegetable products Journal of Food Technology and
biotechnology 39 (4 ):305-11.

Sargent SA, Ritenour MA, Brecht JK. 2000 Handling, cooling and sanitation
techniques for maintaining postharvest quality

Schlimme DV, Rooney ML. 1994. Packaging of minimally processed fruits and
vegetables. In: Wiley RC, editor. Minimally processed refrigurated fruits
and vegetables New York: Champman & Hall, Inc.

Schouten RE, Van Kooten O. 2000. Genetic and physiological factor affecting
color and firmness. In: Steele R, editor. Understanding and measuring the
shelf-life of food. Corporate Blvd. NW and Boca Raton FL. : CRC Press
LLC. p 69-90

Schuchat A, Swaminathan B, Broome CV. 1991. Epidemiology of human
listeriosis. Clin Microbiol Rev 4:169-83.

Senesi E, Galvis A, Fumagalli G. 1999. Quality indexes and internal atmosphere
of packaged fresh-cut pears. Journal of Food Science 11(2):111-20.

Senter SD, Cox NA, Bailey JS, Forbus Jr. WR. 1985. Microbiological changes in
fresh market tomatoes during packing operations. Journal of Food
Science 50(1):254-5.

70

Simon A, Gonzalez-Fandos E, Tobar V. 2004. Influence of washing and
packaging on the sensory and microbiological quality of fresh peeled white
asparagus. Journal of Food Science 69(1):FMS 6-12.

Sinigaglia M, Albenzio, M., Corbo, MR. 1999. Influence of process operations on
shelf life and microbial populations of fresh cut vegetables. Journal of
Industrial Microbiology and Biotechnology 23:484-8.

Siomos AS, Sfakiotakis EM, Dogras CC. 2000 Modified atmosphere packaging
of white asparagus spears: composition, color and texture quality
responses to temperature and light. Sci Hortic 8421-13.

Sivapalasingam S, Friedman CR, Cohen L, Tauxe RV. 2004. Fresh Produce: A
growing cause of outbreaks of foodborne illness in the United States, 1973
through 1997. Journal of Food Protection 67(10):2342-53.

Smith JP, Ramaswamy HS. 1996. Packaging of fruits and vegetables. In:
Somogyi L, Ramaswamy, H.S., Hui, Y.H., editor. Processing fruits:
science and technology. Lancaster, PA: Technomic Publishing Co.

Suslow TV. 1997. Postharvest Chlorination: Basis properties and key points for
effective disinfection. Resources Publication 8003.

Suslow TV. 2000. Chlorination in the produciton and prostharvest handling of
fresh fruits and vegetables Chapter 6. p 3 - 11

Talasila PC, Chau KV, Brecht JK. 1995. Design of rigid modified atmosphere
packages for fruits and vegetables. Journal of Food Science 60(4):758-61.

Taylor CB. 1979. Marketing michigan asparagus: Potentials for fresh market
expansion. East Lansing: Michigan State University.

Ternorio MD, Villanueva MJ, Sagardoy M. 2004. Change in carotenoids and
chlorophylls in fresh asparagus (Asparagus officinalis L.) stored under
modified atmosphere packaging. Journal of science food agriculture
842357-65.

Ternorio MD, Villanueva MJ, Sagardoy M. 2005. Physical, chemical, histological
and microbiological changes in fresh green asparagus (Asparagus
officinalis, L.) stored in modified atmosphere packaging Food Chemistry
91(4): 609-19.

Tewari G. 2002. Microbial control by packaging. In: Vijay K, Juneja VK, Sofos JN,
editors. Control of foodborne microorganisms. New York Marcel Dekker. p
191-208.

Thompson AK. 1998. Controlled Atmosphere Storage of Fruits and Vegetables. 1
ed. Oxon ; New York: CAB International. 81-116 p.

71

Toumas VH. 2005. Spoilage of vegetable crops by bacteria and fungi and related
health hazards.

Troller JA. 1993. Sanitation in Food Processing 2 ed. San Diago: Academic
Press. 52-62 p.

UCANR. 1997. Table on compatible fresh fruits and vegetables during 7 day
storage. Publication 21560 Division of Agriculture and Natural Resource:
University of California.

University of Florida. 2000. A Vegetable Crops Extension Publication. In:
University of Florida Institute of Food and Agricultural Sciences
Cooperative Extension Service, editor.

USDA. 1995. Protecting perishable foods during transport by truck: US.
Department of Agriculture. Transportation and Marketing Division,
Handbook No. 669. September.

USDA. 2006. Vegetables 2005 summary. National Agricultural Statistics Service.
United States Department of Agriculture. .

\fillanueva MJ, Tenorio MD, Sagardoy M, Redondo A, Saco MD. 2005. Physical,
chemical, histological and microbiological changes in fresh green
asparagus (Asparagus officinalis, L.) stored in modified atmosphere
packaging. Food Chemistry 91(4):609-19.

Voisey PW, Crete R. 1973. A technique for establishing experimental conditions
for measureing food firmness to simulate consumer evaluations. Journal
of Texture Studies 4:371-7.

Watada AE. 1997. Quality maintenance of fresh-cut fruits and vegetables. Foods
and Biotechnol 6(4):229-33.

Watkins CB. 2000. Responses of horticultural commodities to high carbon
dioxide as related to modified atmosphere packaging. HortTechnoIogy
10:501-5.

Whitaker JR, Lee, CY. 1995. Recent advances in chemistry of enzymatic
browning. In: Lee CY, Whitaker, J.R., editor. Enzymatic browing and its
prevention. Washington, DC: American Chemical Society. p 2-7.

Wilson LG, Boyette MD, Estes EA. 1999. Postharvest handling and cooling of
fresh fruits, vegetables, and flowers for small farms. Part I: quality
maintenance North Carolina State University: Horticulture lfformation
Leaflets.

72

World Horticultural Trade & U.S. Export Opportunities. 2005. World Asparagus
Situation and Outlook. Foreign Agricultural Service, US. Department of
Agriculture.

Young GL, Wooster JJ. 1996. Designing packages for fresh-cut produce. Tappi
Journal 79(6 ):205-11.

Zagory D. 1995. Principles and practice of modified atmosphere packaging of
horticultural commodities. In: Farber JM, Dodds, K.L., editor. Principles of
modified atmosphere and sous vide product packaging. Lancaster, PA
Technomic Publish Co. .

Zagory D. 1998. An update on modified atmosphere packaging of fresh produce.
Packaging International 1 17: 1 -5.

Zagory D. 1999. Effect of post-processing handling and packaging on microbial
populations. Postharvest Biology Technology 15 (3):313—21.

Zagory D, Kader AA. 1988. Modified atmosphere packaging of fresh produce.
Food Technology 42(9 ):7-77.

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3 THE SHELF LIFE OF FRESH-CUT MICHIGAN ASPARAGUS PACKED IN
MAP AND VSP MICROWAVEABLE TRAY SYSTEMS AT 1°C AND 8°C
STORAGE TEMPERATURES

Abstract

Asparagus (Asparagus officinalis L.) is a perennial vegetable of the lily
family (Liliaceae). The world consumption and the proportion eaten as fresh
asparagus grew rapidly from 1997 to 2005 and was more than was canned or
frozen. Fresh asparagus is a very perishable crop because of its high post-
harvest metabolic rate. In order for Michigan (currently ranked 3rd in the nation for
asparagus production) asparagus to remain competitive, the industry needs to
focus on value addition to help Michigan asparagus growers in a global
asparagus marketplace. Modified atmosphere packaging (MAP) has been used
successfully to extend shelf life of fresh fruits and vegetables by reducing their
respiration rate. Vacuum skin packaging (VSP) can also be used with fresh
produce to increase product shelf life by creating a micro-atmosphere around the
product. The objective of this study was to determine the quality and shelf life of
fresh-cut Michigan asparagus packed for the retail market in MAP and VSP
microwaveable tray systems. Pre-trimmed, cleaned, 6-inch fresh asparagus
spears were packed in microwaveable tray systems using passive MAP and VSP
techniques. Both systems were heat-sealed with highly permeable films provided
by commercial manufacturers, and stored at 1°C and 8°C. To evaluate product
shelf life and quality, three packages from each treatment were selected
randomly every third day and evaluated for weight loss, moisture content, pH,

O2/CO2 content in the package headspace, microbial growth and sensory quality.

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MAP and VSP techniques and storage temperature affected the quality and shelf
life of fresh-cut Michigan asparagus. Based on sensory scores, the shelf life of
asparagus stored under MAP at 1°C and 8°C, 80% RH (18 days at 1°C, 15 days
at 8°C) was longer than that stored under VSP at the same temperatures (9 days
at 1°C and 3 days at 8°C). MAP at 1°C resulted in product with the highest

quality and longest shelf life.

3.1 Introduction

Asparagus (Asparagus officinalis L.) is one of the most highly consumed
vegetables. Green asparagus is the popular edible form in the US market (Luo
2006). Michigan ranks third in the nation for asparagus production and produces
up to 25 million pounds annually (Michigan Asparagus Advisory Board; MDA
2005; World Horticultural Trade & U.S. Export Opportunities 2006).

Asparagus is a highly perishable crop because of its high metabolic
(respiration) postharvest rate, >60 mg CO2/kg/h (Fallik 2004). Modified
atmosphere packaging (MAP) is a preservation technique which can maintain the
product’s storage shelf life. MAP can reduce the respiration rate of fresh produce,
ethylene production and moisture loss, and help to maintain the product’s
nutritional value and edibility by adjusting gas atmosphere inside the package, in
conjunction with a wide-range of permeable polymeric films to preserve
freshness and quality (Thompson 1998).

Commodities vary in their respiration rate and in their tolerance to the
amount of available O2 and CO2. Fresh asparagus has a high metabolic rate and

its tolerance level to CO2 is less than 10% concentration at 3-6°C and less than

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15% at 0-3°C. O2 levels less than 10% lead to discoloration (Kader 1989a;
Saltveit 1989; Ooraikul 1991; Kader 1993). The recommended modified
atmosphere levels of O2 and CO2 to preserve the shelf life of fresh asparagus is
20% O2 and 5-10% CO2 (Kader1985).

Vacuum skin packaging (VSP) is another technique which can maintain
freshness and extend the shelf life of fresh produce using a themoforrnable film
to vacuum-seal the product against a rigid backboard (Tewari 2002). It can retard
the growth of microorganisms, resulting in a decrease in spoilage (Buick 2006).
Generally, vacuum packaging helps to preserve product appearance better than
MAP (Beltran 2005). However, the published research using vacuum packaging
with fresh produce is minimal.

Controlling respiration is a big challenge in designing packages for fresh-
cut produce. Permeable films have been developed to use with MAP and
vacuum packaging to allow the product inside the package to breathe.
Permeable films can help to prevent moisture loss, decelerate produce
senescence, reduce degradation of product quality and preserve the shelf life of
produce (Schlimme 1994). Permeable plastic films have been created by many
manufacturers for use with fresh produce to control gas transmission rates and
gas exchange between the package head space and the external environment
(Zagory 1998). However, the choice of film permeability depends on the
respiration rate of the fresh produce (Kader 1989b; Paine 1992; Day 1993).

Temperature is also a key factor in maintaining the shelf life of fresh

produce as it affects the metabolic activity of the product (Kader 1989b). Low

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temperature can help to maintain product freshness by delaying its metabolic
reactions and pigment degradation, and by retarding microbial growth (Kader
1989b; Ooraikul 1991 ; Heard 2002; Ternorio MD. 2005).

The main objectives of this study were 1) to determine the shelf life of
fresh-cut Michigan asparagus packed in two commercially available permeable
films and microwavable tray systems: a microwaveable Dupont® tray and a
microwaveable Cryovac® tray using two different techniques: modified
atmosphere packaging (MAP) and vacuum skin packaging (VSP), and 2) to
determine the effect of different storage temperatures (1°C and 8°C) on the shelf
life of fresh packaged asparagus.

3.2 Materials and Methods
3.2.1 Sanitation, packaging and storage

Fresh, green Michigan asparagus was provided by the Michigan
Asparagus Advisory Board from 3 different locations (from the middle of May to
the middle of June). After arrival, fresh asparagus was rapidly transported to a
chamber (3°C) in laboratory facilities at the School of Packaging (Packaging
Building) and the Trout Food Science and Human Nutrition building. Asparagus
spears were washed with tap water and deionized distilled water to remove soil,
debris and other contamination and then sanitized by dipping in a 100 ppm
sodium hypochlorite solution (Cleaner and Sanitizer, Johnson® CRS, US) for 1
minute and then rinsed twice with distilled water. The medium to large diameter
spears were sorted, dried off with sanitized paper toweling (using UV light for 20-

30 minutes) and trimmed to a length of 6 inches. Trimmed fresh asparagus

77

spears were then packed in the microwaveable containers. Two types of
packaging techniques were used: modified atmosphere packaging (MAP) and
vacuum skin packaging (VSP). A Multivac T-200 machine (Multivac, Inc., Kansas
City, MO.) was used for both techniques. Products were then stored in controlled
chambers at 1°C and 8°C, 80% RH for 18 days. The asparagus used for the
MAP and VSP treatments were from different harvest times. Fresh-cut asparagus
packaged in MAP and VSP trays are shown in Figure 3.1.

Modified Atmosphere Packaging (MAP): 453 g (1 lb) of pre-trimmed spears were
packed in the Dupont® microwaveable trays (5% inX71/z inX11/2 in, Polypropylene,
Dupont®, Dura Freshm, Wilmington, DE). A passive modified atmosphere was
established and heat-sealed in medicated air containing 21% O2, and 0.03 %
CO2, over a pressure of 80 psi. A Iidding film from Dupont®was used to seal the
containers (Appeel Lidding Sealant Resin 004, 2.5 mils thickness, O2
permeability of 7.75 cc.mil/in2.day.atm and CO2 permeability of 8.0
cc.miI/in2.day.atm).

Vacuum Skin Packaging (\_/SP): The vacuum skin packaging technique was used
to pack the samples in Cryovac® microwaveable trays (41/2 in x 63/4 in x 1% in,
CS966-B2, Cryovac®, Simple StepsT", Duncan, SC). Each tray contained 133 g
(0.29 lb) of asparagus spears and was vacuum-sealed with a Cryovac® Iidding
film (3 mils thickness, O2 permeability of 10.64 cc.milfln2.day.atm and CO2
permeability of 60.77 cc.miI/in2.day.atm). The quantity of spears packed in to the

Cryovac® containers was lower because of the limitations of the VSP system.

78

 

 

 

 

MAP tray VSP tray
Figure 3.1: Fresh-cut Michigan asparagus packed in a MAP tray and a VSP tray

3.2.2 Product Evaluation

Product analysis was conducted on the stored samples by taking three
trays of each packaging type and temperature, using a 3 day frequency.
Triplicate analyses of each parameter for each of the trays were done on the
samples. The process is illustrated in Appendix A.
3.2.2.1 Weight loss

For every 3 day evaluation, three MAP trays and three VSP trays from the
two storage temperatures were weighed to determine the weight loss over the
storage time using a precision balance scale (NSF®, Arlington, VA). The weight
loss from the product trays for each evaluation period was calculated from the
average weight of three samples of each storage temperature.
3.2.2.2 Moisture Content

Whole spears were chopped into small pieces (about 1 inch), and a
sample weight of 15 - 16 g was placed into an aluminum pan. Aluminum pans
containing the chopped asparagus were placed in a vacuum oven (524 Treas,

Precision Scientific) at 100°C (212°F) for 4 hours and then reweighed after

79

cooling to determine the moisture content (AOAC 1984). Moisture content was
calculated on a wet basis which is expressed as the loss in weight of asparagus
after drying compared to the product fresh weight.
3.2.2.3 Headspace gas analysis

Oxygen (O2) and carbon dioxide (CO2) concentrations in the headspace of
the tray were monitored using an O2/CO2 gas analyzer (Illinois 6600 Head Space
Analyzer, Illinois Instruments, Inc., Johnsburg, IL). To avoid gas exchange with
the surrounding atmosphere during quantification, a septum (septum PPL-
193456, Illinois Instruments, lnc., Johnsburg, IL) was placed onto the film surface
of the packages.
3.2.2.4 pH analysis

Whole asparagus spears were randomly selected from each treatment. 15
g of product were blended in a blender and made up to a final volume of 100 ml
using Milli Q water. The pH of the solution was measured using a pH-meter
(Corning 440 benchtop pH meter, Corning®, NC).
3.2.2.5 Microbial analysis

Asparagus spears were randomly selected from each packaging system
and storage condition. 25 g of sample were placed into a sterile Whirl-Pack®
Sampling bag (6 a 9 inch polyethylene bag, Whirl-PackT'“, Nasco, Fort Atkinson,
WI) and then homogenized with 100 ml of sterile 0.1% peptone water (Bacto
Peptone, Difco", Becton Dickinson and Company, USA) in a stomacher (Seward
Stomacher 400 lab system, Seward Medical, London, UK) for 2 minutes at high

speed. Serial dilutions (10", 10*, 10:3, 10*1 and 10") were made from 1 ml of the

80

asparagus/fluid mixture with 9 ml of sterile 0.1% peptone water in sterile tubes.
Duplicate samples of each treatment were plated on the following specific media
(APHA 1984; Villanueva MJ. 2005 ), as shown below, using an automatic spiral
plating machine (AutoPlate 4000, Spiral Biotech®, Inc., MA). Microbial plate
counts were determined as average values of duplicate measurements and
reported as logarithmic values of colony-forming units per gram of sample (Log 10
CFUlg).

a Total count bacteria was determined by spiral-plating 0.1 ml of the diluted
samples in duplicate on Trypticase Soy Agar or TSAYE-C (Difcom, Becton
Dickinson and Company, USA) containing 0.6% yeast extract and 100 ppm
cyclohexamide (Sigma-Aldrich Co., St. Louis, MO). TSAYE-C plates were
counted after 2-3 days of incubation at 35°C. Ranges of total count bacteria were
25-250 per plate.

:1 Yeasts and molds were determined by spiral-plating 0.1 ml samples on potato
dextrose agar (PDA) (Difcom, Becton Dickinson and Company, USA) containing
20 ppm streptomycin (Sigma) and 50 ppm ampicillin (Sigma-Aldrich Co., St.
Louis, MO). PDA plates were counted after 3-7 days of incubation at 23°C (room

temperature). Countable ranges of yeast and mold were 15-150 per plate.

a E. coli and coliforms were determined by spiral-plating 1 ml of samples on 3M
Petri films (3M PetrifiImTM, MN). The films were counted after 24 hours of
incubation at 35°C.

3.2.2.6 Sensory evaluation

According to the green asparagus quality guideline (Michigan Asparagus

81

Advisory Board 2005), the appearance of fresh, green Michigan asparagus
should be a dark green-violet color with a firm texture and tightly closed and
compact heads and tips. The stalks should be straight, and tender with shiny
stem appearance. Visual and organoleptic characteristics of the samples were
monitored to determine quality attributes and product shelf life during storage
using a 9-12 member trained panel. MSU students (age between 26-30 years)
served as panelists and were selected on the basis of their ability to detect
specific product attributes (including odor, color and texture). All panelists
participated in the training which was conducted over a 4 month period.

Standard asparagus color and quality scales were created according to
the characteristics of fresh Michigan asparagus and its deterioration features
including stalk and tip sections, odor and texture. Fresh product was used in
training in addition to unacceptable product (the end of the shelf life) in order to
give the panelists a range of attribute intensities.

Color, odor, texture (crispness/freshness) and overall quality were
evaluated using a 5-point category scale, where 5 represented the best (fresh)
and 1 was the worst (spoiled). The sensory testing was conducted in the Sensory
Laboratory, Trout Food Science and Human Nutrition building at Michigan State
University. Statistical analysis of the sensory data was performed using the

statistical software program, SAS version 8.01.

82

3.3 Results and Discussion

3.3.1 Weight Loss

Loss of weight from both tray systems during 18 days storage at two

temperatures is shown in Table 3.1. Weight loss of the products was observed in

both treatments and both storage conditions. The loss in weight of fresh-cut

asparagus in the MAP system was lower than that in the VSP system at both

storage temperatures. The loss of product weight in both packaging systems was

slower at 1°C than at 8°C. However, the difference in weight loss was not

substantial. The loss of product weight was delayed due to the water vapor

barrier protection from the polypropylene based microwaveable tray materials

and a Iidding film which is also a good water vapor barrier.

Table 3.1: The moisture content of fresh-cut Michigan asparagus stored at 1°C
and 8°C, 80% RH under MAP and VSP systems during 18 days storage

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

% Weight Loss % Moisture Content
Samples Days 1,, C 8° C 1 o C 8° C
0 00010.00 0.001000 93.321043 93.321043
3 0.001000 00010.00 93.301024 930010.60
6 0.001000 00010.00 932810.44 92.831066
MAP 9 00010.00 00010.00 932510.59 932510.36
12 00010.00 01810.14 932610.31 93.191073
15 0.141016 03010.13 932010.50 93.141047
18 0.181014 03010.13 93.171056 93.101068
0 00010.00 00010.00 93.691043 93.691043
3 0.001000 0.001000 93.641036 93.641026
VSP 6 00010.00 01310.32 93.601033 93.551031
9 0.001000 02510.38 93.581033 93.541040
12 02510.39 0.621056 93.571029 93.541046

 

83

 

3.3.2 Moisture Content

The moisture content of fresh Michigan asparagus on day 0, prior to
storage, was approximately 93.32%. A decrease in moisture content of the
samples packed in both MAP trays and VSP trays at 1°C and 8°C was observed.
In the MAP system, loss of moisture content at 1°C (0.15%) was slightly less
than that at 8°C (0.23%) over the storage time as illustrated in Table 3.1 and
Figure 3.2.

Loss in moisture content of asparagus packed in the VSP system at 1°C
and 8°C also occurred as shown in Table 3.1 and Figure 3.3. Loss of moisture
content from the VSP of product at 8°C (0.16%) was almost the same as that at
1°C (0.13%) over the storage time.

There was no significant difference (p>0.05) in moisture loss during
storage for MAP at 1°C and also at 8°C. The same result was found for VSP at
1°C and 8°C. There was no significant difference (p>0.05) between the two
storage temperatures for each treatment on the same evaluation day. The
moisture content of fresh-cut asparagus in MAP and VSP and stored at 1°C and

8°C remained satisfactory over the entire storage time.

84

 

 

% Moisture content

 

 

O 3 6 9 12 15 18 Days

I MAP 1°C I MAP 8°C

Figure 3.2: Moisture content of fresh-cut Michigan asparagus stored in MAP at
1°C and 8°C, 80% RH during storage

 

75.00-

50.00~

  

 

% Moisture content

N
.0 .U‘
o o
o o
1 I

 

IVSP 1°C IVSP 8°C

Figure 3.3: Moisture content of fresh-cut Michigan asparagus stored in VSP at
1°C and 8°C, 80% RH during storage

85

3.3.3 Headspace gas Analysis
Oxygen (O2) and carbon dioxide (CO2) concentrations inside the MAP and

VSP packages at both temperatures changed during the experimental storage
time because of the respiration process of the fresh asparagus, the metabolism
of contaminated microorganisms and the gas exchange between the interior and
exterior atmospheres through the permeable film and tray. This analysis was only
able to be done on the MAP system. Samples stored in VSP system at both 1°C
and 8°C could not be measured because of the product spoilage that caused
liquid in the package, to accumulate and there was not enough room for
sampling the gas. The gaseous atmosphere in the MAP is shown in Table 3.2,
and it is represented in Figure 3.4, for O2 and Figure 3.5, for CO2. The initial gas
concentration inside fresh-cut asparagus in the MAP system was medical air,
composed of 21% O2 and 0.03 % CO2 while the O2 and CO2 concentration initially
in the package headspace under VSP system was 0%. It is difficult to achieve a

complete vacuum and to remove all of the air from the package (lrtwange 2006).

A change in gaseous atmosphere inside the packaging system occurred.
The level of O2 went down while CO2 increased due to the consumption of O2
and production of CO2. 02 and CO2 levels inside the MAP at 1°C changed
moderately from the initial values of 21% O2 and 0.03% CO2 before stabilizing at
around 19% and 3%, respectively, and reached equilibrium after day 3, for O2
and day 6, for CO2.

At 8°C, oxygen concentration of the asparagus-packed MAP reached
equilibrium after day 6, while carbon dioxide continued to increase and reached

equilibrium about day 9.

86

Table 3.2: O2 and CO2 concentration in fresh-cut Michigan asparagus in MAP at

1°C and 8°C, 80% RH during storage

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Da 3 MAP at 1°C MAP at 8°C
y average % 02 average %CO2 average %O2 average %C02
0 20.901000 0.031000 20.901000 0.031000
3 192710.36 2.551056 190510.68 3.651099
6 19.321018 3.121012 18.601054 3.771084
9 19.301023 3.051023 18.421052 4.551050
12 19.231023 3.031036 18.301054 4.471079
15 19.451012 3.071044 18.301033 4.381069
18 18.881017 3.381071 18.331036 4.351058
25
20 — \ ! I I I '
.___ _—_-_
N 15 ~
O
.\°
10 —
5 _
0 I I F I I

12 15

18 Days

 

 

+MAP1°C +MAP 8 °C

Figure 3.4: 02 concentration in fresh-cut Michigan asparagus in MAP at 1°C and
8°C, 80% RH during storage

87

 

 

 

 

0 T T I I I l
0 3 6 9 12 15 18 Days

 

-O-MAP1°C -D-MAP 8 °C

Figure 3.5: CO2 concentration in fresh-cut Michigan asparagus in MAP at 1°C
and 8°C, 80% RH during storage
3.3.4 pH Analysis

pH of fresh-cut Michigan asparagus decreased slightly over the storage
time for each treatment. There was no significant difference (p > 0.05) in the pH
of the asparagus-packed MAP at 1°C and 8°C, and between the two storage
temperatures on the same evaluation day as shown in Figure 3.6. For VSP
asparagus, there was no significant difference (p > 0.05) in pH between the two
storage temperatures at the same evaluation day as illustrated in Figure 3.7.
However, the pH decreased significantly over storage for product stored in VSP
at 8°C and at 1°C, day 12.

The decrease in pH values of samples stored under MAP and VSP at 1°C

occurred more slowly than at 8°C. The difference in the pH between the MAP

88

samples at the two storage temperatures was not as much as for the VSP

samples.

 

6.50 '

6.20

5.90 ~

5.60 1

pH

5.30 -

5.00 ~

4.70 -

 

 

 

4.40 - - , , f -
o 3 6 9 12 15 18 Days

'0'MAP 1°C +MAP 8°C

Figure 3.6: The pH of fresh-cut Michigan asparagus stored in MAP at 1°C and
8°C, 80% RH during storage

 

6.50

6.20 -

L
\ $

5.60 1

 

 

 

I I
o.
5.30 —

5.00 1

4.70 ~

 

 

 

4.40 - , - f
0 3 6 9 1 2 Days

-<>-VSP 1°C +VSP 8°C
Figure 3.7: The pH of fresh-cut Michigan asparagus stored in VSP at 1°C and
8°C, 80% RH during storage

89

3.3.5 Microbial analysis

The microbial growth on fresh-cut Michigan asparagus stored under MAP
and VSP at both 1°C and 8°C increased as indicated in Table 3.3. Microbial
analysis of VSP asparagus at both 1°C and 8°C is reported for only 9 storage
days due to the deterioration of the product. The initial microbial load in MAP and
VSP was different since these two experiments used asparagus from different
lots.

The numbers of microorganisms on fresh-cut asparagus stored under
MAP at 1°C was lower than that at 8°C. The total count population of bacteria in
MAP trays increased from 5.08 log-o CFU/g from the initial time point (day 0) to
7.57 log1o CFU/g at 1°C, and 7.84 Iog1o CFU/g at 8°C as shown in Figure 3.8.
Yeast and mold counts increased from 4.58 log-o CFU/g to approximately 6.62
log-o CFU/g for asparagus in the MAP package at 1°C and 7.63 10910 CFU/g for
MAP product at 8°C as illustrated in Figure 3.9. The growth of coliforms in
modified atmosphere packed-asparagus stored at 1°C and 8°C was initially 3.48
log-o CFU/g and gradually increased to 3.90 logto CFU/g at 1°C and 3.97 log-o
CFU/g at 8°C as illustrated in Table 3.3.

The growth of bacteria on fresh-cut asparagus packed in VSP was slightly
lower at 1°C than at 8°C, from 5.01 Iog1o CFU/g at the beginning, to 8.74 log-o
CFU/g and 8.88 log1o CFU/g, respectively. This trend line is about the same as
shown for bacterial growth in MAP packages shown in Figure 3.10. The yeast
and mold loads on the VSP asparagus was initially lower than for the MAP

product, but in 9 days the yeast population of the VSP product at 1°C and 8°C

90

grew to 7.28 Iog1o CFU/g and 7.62 logm CFU/g, respectively. This was much
higher than that of the MAP product at both storage conditions as shown in
Figure 3.11. The coliform population in the VSP packaged asparagus stored at
1°C and 8°C on first storage day was 3.52 logm CFU/g. At the end of shelf life
(day 9, based on sensory evaluation), the number had risen to 3.60 logm CFU/g
and 4.30 log1o CF U/g, respectively as shown in Table 3.3.

Table 3.3: Microbial populations on fresh-cut Michigan asparagus stored in MAP
and VSP at 1°C and 8°C, 80% RH during storage

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Microbial Quantity (Log1o CFUIg)
Sample Days Total Count Bacteria Yeast and molds Coliforms
0 5.081023 4.581025 3.481025
3 5.171045 5.181019 3.671019
6 6.121034 5.511016 3.801016
MAP 1°C 9 6.361033 6.451057 3.871057
12 6.521021 62610.31 3.901031
15 6.911039 6.561024 3.871024
18 7.571005 6.621039 3.901039
0 5.081023 4.581025 3.481025
3 6.001048 5.591049 3.751049
6 7.591017 6.121093 3.821093
MAP 8°C 9 7.001081 6.791058 3.851058
12 7.181036 7.591037 3.881037
15 8.191064 7.621036 3.951036
18 7.841052 7.631080 3.971080
0 5.011001 3.301021 3.521021
VSP 1°C 3 6.561022 6.391019 3.121019
6 62810.07 6.821008 3.671008
9 8.741010 7.281013 3.601013
0 5.011001 3.301021 3.521021
VSP 8°C 3 6.831008 6.931008 3.601008
6 7.101005 7.001000 3.671000
9 8.881009 7.621011 4.301011

 

91

 

Total Count Bacteria

 

10.00

 

Population recovered
(Log CFUIg)

2.00 1

 

 

 

0.00 I I I I I I
0 3 6 9 12 15 18 Days

'0- MAP 1°C '0' MAP 8°C

Figure 3.8: Bacterial growth on fresh-cut asparagus in MAP at 1°C and 8°C, 80%
RH during storage

Yeast and Molds

 

10.00

8.00 1

 
   

Population recovered
(Log CFUIg)
9’
O
O

.N .8
O O
O O
l 1

 

 

 

0.00 I I I I I I
o 3 6 9 12 15 18 Days

'0- MAP 1°C +MAP 8°C

Figure 3.9: The growth of yeast and molds on fresh-cut asparagus in MAP at 1°C
and 8°C, 80% RH during storage

92

Total Count Bacteria

 

10.00

8.00 1

6.00 /

4.00 1

 

 

Population recovered
(Log CFUIg)

2.00 -

 

 

 

0.00 - - -
0 3 6 9 Days

-<>-VSP 1°C +VSP 8°C

Figure 3.10: Bacterial growth on fresh-cut asparagus in VSP at 1°C and 8 °C,
80% RH during storage

Yeast and Molds

 

10.00

 

W

Population recovered
(Log CF Ulg)

2.00 1

 

 

 

0.00 - - -
0 3 6 9 Days

'O'VSP 1°C +VSP 8°C

Figure 3.11: The growth of yeast and molds on fresh-cut asparagus in VSP at
1°C and 8°C, 80% RH during storage

93

3.3.6 Sensory evaluation

The trained panel sensory evaluation results for fresh-cut Michigan
asparagus are shown in Table 3.4. The quality of MAP asparagus, stored at 1°C
was acceptable for more than 18 days while the shelf life of MAP asparagus
stored at 8°C was approximately 18 days due to the change in stalk color and
unpleasant odor as illustrated in Table 3.5 and Figure 3.12. Quality parameters
included stalk color, tip color, texture, odor and acceptability of overall
appearance as evaluated by 9-12 trained panelists.

Samples stored in VSP spoiled very fast and a 9 day storage life was
found at 1°C. At 8°C, the shelf life of asparagus VSP was 3 days. At the end of
the experiment, the asparagus stored in the VSP had an unacceptable smell,
watery, spoiled tips and dark green/purple in color.

The asparagus used in the VSP experiment was delivered near the end of
the Michigan asparagus season. This affected the initial quality of the asparagus
used in this treatment, which can be seen in Table 3.6 and Figure 3.13. At day 0
(initial day), sensory scores of fresh asparagus used for the VSP (overall quality
score = 3, still marketable-aging, deterioration but still expectable) were lower
than that of fresh asparagus used for MAP product (overall quality score = 5, very
fresh/best). Moreover, due to the vacuum delivered in the VSP process, the tips

of the asparagus spears were squeezed, resulting in some bruising and rot.

94

Table 3.4: Panelist’s response (mean) for fresh-cut Michigan asparagus stored in
MAP and VSP at 1°C and 8°C, 80% RH

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Color Overall
Samples Days Stalk Tip Texture Odor Quality
0 50° 50° 50° 50° 50°
3 50° 50° 50° 48° 50°
6 43° 43° 42° 45° 43°
MNDPC 9 40° 45° 42° 45° 43°
12 32° 37° 39° 42° 39°
15 38° 43° 41° 38° 49°
18 28° 39° 34° 35° 34°
0 50° 50° 50° 50° 50°
3 50° 50° 50° 47° 50°
6 40° 41° 40° 42° 42°
NMPWC 9 34° 37° 39° 40° 40°
12 32° 35° 33° 33° 31°
15 30° 34° 31° 30° 31°
18 29° 32° 38° 27° 29°
0 31° 36° 41° 34° 33°
3 34° 36° 39° 37° 40°
vabvc 6 34° 27° 37° 33° 31°
9 30° 25° 35° 30° 30°
12 33° 30° 38° 25° 21°
0 31° 36° 41° 34° 33°
3 34° 29° 37° 29° 31°
\$P8€ 6 28° 27° 37° 20° 18°
9 31° 21° 35° 15° 14°
12 25° 15° 25° 10° 10°

 

 

3" Means within a column, which are not followed by a common superscript letter,
are significant difference (p<0.05).

95

Table 3.5: Effect of storage temperature on sensory characteristics of fresh—cut
Michigan asparagus stored in MAP

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Samples Days Stalkcomrl’ip Texture Odor Overall Quality
0 5.0 5.0 5.0 5.0 5.0
3 5.0 5.0 5.0 4.8 5.0
6 4.3 a 4.3 4.2 a 4.5 a 4.3

MAP 1°C 9 4.0 a 4.5 a 4.2 a 4.5 a 4.3 a
12 3.2 3.7 a 3.9 a 4.2 a 3.9 a
15 3.8 a 4.3 a 4.1 a 3.8 a 4.3 a
18 2.8 3.9 a 3.4 a 3.5 a 3.4 a
0 5.0 5.0 5.0 5.0 5.0
3 5.0 5.0 5.0 4.7 5.0
6 4.0 b 4.1 4.0 b 4.2 b 4.2

MAP 8°C 9 3.4 b 3.7 b 3.9 b 4.0 b 4.0 b
12 32 35° 33° 33° 31°
15 3.0b 3.4b 3.1b 3.0b 3.1 b
18 29 32° 38° 27° 29°

 

a” Means within a column, which are not followed by a common superscript letter,
are significant difference (p<0.05).

Table 3.6: Effect of storage temperature on sensory characteristics of fresh-cut
Michigan asparagus stored in VSP

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Samples Days StalkcmorTip Texture Odor Overall Quality
0 3.1 3.6 4.1 3.4 3.3
3 3.4 3.6 a 3.9 3.7 a 4.0 a

VSP 1°C 6 3.4 a 2.7 3.7 3.3 a 3.1 a
9 3.0 2.5 a 3.6 3.0 a 3.0 a
12 3.3 a 3.0 a 3.8 a 2.5 a 2.1 a
0 31 36 41 34 33°
3 3.4 2.9 b 3.7 2.9 b 3.1 b

VSP 8°C 6 2.8 b 2.7 3.7 2.0 b 1.8 b
9 3.1 2.1b 3.5 1.5b 1.4”
12 25° 15° 25° 10° 10°

 

a” Means within a column, which are not followed by a common superscript letter,
are significant difference (p<0.05).

 

 

Average Score

 

Stak color

 

 

15

18

 

Odor

 

 

 

 

36912151

8

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Tpcobr Texture
510 e 5-e
0 e
-. O
4‘ . . z . 4 ' 8 C .
e . .
3- 3- 9
2- 2-
1 1
0369121518 0369121518
Overalquaity
51. e
4 0 : e PKG
' O
. e MAP1C
3‘ ’ ’ e e MAP8C
2-1
1
0 3 6 9 121518

Days

Figure 3.12: The sensory quality of fresh-cut Michigan asparagus packed in

MAP tray at 1°C and 8°C, 80% RH during 18 days of storage

Average Score

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Stalk color Tip color Texture
5- 5- 5-
4-I 4-1 4 .
Q Q 1 3 O . .
e e .
3-0 , 0 3- e . o 31
e e e
2- 21 0 21
e
1- 11 11
0 3 6 9 12 0 3 6 9 12 o 3 6 9 12
Odor Overall quality
5- 5-
41 . 4- o PKG
e e
3‘ . e . 3_e . . VSP1C
o O VSPBC
2- e 2- o
O . .
1- e 1- e
I I I I I I I l I I
0 3 6 9 12 o 6 9 12
Days

Figure 3.13: The sensory quality of fresh-cut Michigan asparagus packed in VSP
tray at 1°C and 8°C, 80% RH during 18 days of storage

97

3.4Conclusion

Modified atmosphere packaging (MAP), vacuum skin packaging (VSP)
and temperature affect the quality and shelf life of fresh-cut Michigan asparagus.
Based on sensory evaluation, the shelf life of fresh asparagus stored in MAP at
1°C was slightly more than 18 days and at 8°C, it was 18 days, which was longer
than that stored under VSP at 1°C, (9 days) and at 8°C (only 3 days). As
mentioned, the quality of asparagus used for VSP was not as good as that used

for MAP. This might affect the shelf life of asparagus stored in VSP.

The initial quality of a fresh product is very important in overall quality
maintenance and shelf life of product. Proper sanitization is also necessary to
reduce the microbial load that causes the deterioration, and to preserve the
quality of fresh-cut asparagus longer. 100 ppm sodium hypochlorite solution (with
out controlling the pH) might not be able to provide the necessary sanitation level

for fresh-cut asparagus.

The VSP technique that was used with the fresh-cut asparagus needs to
be improved to avoid damage due to pressure decrease, which probably resulted
in accelerated deterioration. A suitable vacuum pressure must be employed

when packing fragile products such as fresh asparagus.

98

3.5 Bibliography

AOAC. 1984. Official Methods of Analysis. Association of Official Analytical
Chemists, editor. Virginia.

APHA. 1984. Compendium of Methods for the Microbiological Examination of
Foods. 2 ed. District of Columbia: American Public Health Association.

Beltran D, Selma, M.V., Tudela, J.A., Gil, MJ. 2005. Effect of different sanitizers
on microbial and sensory quality of fresh-cut potato strips stored under
modified atmosphere or vacuum packaging. Postharvest Biology and
Technology 37(1):37-46.

Buick RK, Damoglou, AP. 2006. The effect of vacuum packaging on the
microbial spoilage and shelf-life of ready-to-use sliced carrots. Journal of
the Science of Food and Agriculture 38(2):167-75.

Day BPF. 1993. Fruit and vegetables. In: Parry RT, editor. Principles and
applications of MAP of foods. New York, USA: Blackie Academic and
Professional. p 114-33.

Fallik E, Aharoni, Y. 2004. Postharvest physiology. Pathology and Handling of
fresh produce.

Heard GM. 2002. Microbiology of fresh-cut produce. In: Lamikanra O, editor.
Fresh-cut fruit and vegetable: Science, Technology and market: Boca
Raton: CRC Press. p 188-226.

lrtwange SV. 2006. Application of modified atmosphere packaging and related
technology in postharvest handlng of fresh fruits and vegetables. . Journal
of the CIGR (E-Journal) 8(4):1-12.

Kader AA. A summary of CA requirements and recommendations for fruit other
than pome fruits; 1989a; Wenatchee, Washing ton USA.14-16 June 1989.
Other Commodities and Storage Recommendations. p 303-28.

Kader AA. Modified and controlled atmosphere storage of tropical fruits; 1993;
Proceeding of an International Conference, Chiang Mai, Thailand. 19-23
July 1993. p 239-49.

99

Kader AA, Zagory, D., Kerbel, E.L. . 1989b. Modified atmosphere packaging of
fruits and vegetables. CRC Crit Rev Food Sci 28(1):1-30.

Luo Y, Suslow, T., Cantwell, M., United States Department of Agriculture-
Agricultural Research Service USDA-ARS. 2006. Asparagus.

MDA. 2005. Michigan Agriculture Statistics 2004-2005. Michigan Agriculture
Statistics Service.

Michigan Asparagus Advisory Board. Asparagus in the home garden.

Ooraikul B, Stiles, ME. 1991. Modified Atmosphere Packaging of Food. Watson
DH, editor. New York: Ellis Harwood Limited. 147,170-227 p.

Paine FA, Paine, H.Y. 1992. A handbook of food packaging. 2 ed: Blackie
Academic & Professional. 242-5 p.

Saltveit ME. A summary of requirements and recommendations for the controlled
and modified atmosphere sotrage of harvested vegetables; 1989;
Wenatchee, Washington, USA. Other Commodities and Storage
Recommendations. p 329-52.

Schlimme DV, Rooney, ML. 1994. Packaging of minimally processed fruits and
vegetables. In: Wiley RC, editor. Minimally processed refrigurated fruits
and vegetables New York: Champman & Hall, Inc.

Ternorio M.D. VMJ, and Sagardoy M. . 2005. Physical, chemical, histological and
microbiological changes in fresh green asparagus (Asparagus officinalis,
L.) stored in modified atmosphere packaging Food Chemistry 91(4): 609-
19.

Tewari G. 2002. Microbial control by packaging. In: Vijay K. J, V.K., Sofos, J.N. ,
editor. Control of foodborne microorganisms. New York Marcel Dekker. p
191-208.

Thompson AK. 1998. Controlled Atmosphere Storage of Fruits and Vegetables. 1
ed. Oxon; New York: CAB International. 81-116 p.

100

Villanueva M.J. T, M.D., Sagardoy, M., Redondo, A., Saco, M.D. . 2005 Physical,
chemical, histological and microbiological changes in fresh green

asparagus (Asparagus officinalis, L.) stored in modified atmosphere
packaging. Food Chemistry 91 (4):609-19.

World Horticultural Trade & U.S. Export Opportunities. 2006. World Asparagus

Situation 8: Outlook. Foreign Agricultural Service, US. Department of
Agriculture.

Zagory D. 1998. An update on modified atmosphere packaging of fresh produce.
Packaging International 1 17:1-5.

101

4 SHELF LIFE OF FRESH-CUT GREEN ASPARAGUS IN MAP AND VSP
MICROWAVABLE TRAY SYSTEMS

Abstract

Sales of fresh-cut produce have increased rapidly and have become the
fastest growing part of the fresh produce industry. Asparagus (Asparagus
ofiicinalis L.) is one of the most popular culinary vegetables since it contains a
wealth of fiber and several essential nutrients. It is a very perishable commodity
due to its very high respiration rate (>60 mg CO2/Kg-hr). To maintain product
quality and to satisfy consumer demand as a convenient food, modified
atmosphere packaging (MAP), vacuum skin packaging (VSP) and
microwaveable containers were used to extend the shelf life of fresh-cut
asparagus as a ready-to-eat food product. Asparagus has a short shelf life,
approximately 14 days under refrigerated temperature (2°C). The objective of this
study was to determine the shelf life of fresh-cut asparagus packed in MAP and
VSP microwaveable tray systems at commercial storage conditions, 4°C, 80%
RH. Weight loss, moisture content, O2/CO2 concentration in the package
headspace, product pH, microbial growth, and sensory evaluation were used to
determine the product quality and shelf life. During storage for 21 days, there
was no significant difference (p>0.05) in weight loss, moisture content, pH, the
level of O2/CO2 concentration in the package headspace and growth of
microorganisms between the two packaging systems. MAP maintained the
freshness and shelf life of the fresh-cut asparagus more than 21 days while the

VSP system maintained the product shelf life through 18 days. Both MAP and

102

VSP products can be cooked in the package using a microwave oven to create a
ready-to-eat fresh product.
4.1 Introduction

The consumer demand for ready-to-eat fresh produce is rapidly increasing
due to an interest in healthy food, a well-balanced diet and convenience. This
has helped fresh-cut produce become one of the most popular products in
today’s marketplace (IFPA 2003 ). Asparagus has become one of the most
consumed vegetables in the world.

Asparagus (Asparagus officinalis L.) is a unique perennial vegetable and
is a member of the lily family (Liliaceae) (Hexamer 1901; Peirce 1987; Rubatzky
1997). Green asparagus is the most popular consumed variety in the United
States, Japan, New Zealand, Australia and Chilean markets, and is gradually
becoming more popular in the European market (Esteve 1995; Luo 2006). Like
other fresh fruits and vegetables, fresh asparagus is alive and respiring after
harvesting. Asparagus has a very high respiration rate (>60 mg CO2/Kg-hr),
resulting in a perishable vegetable which has a short shelf life, normally 14 days
(Kader 1986; Kader 1992 ; Fallik 2004).

Freshness is a major quality requirement, which is true of all other fresh
produce. To maintain product quality and to support the growing economics of
the fresh-cut asparagus market, packaging is an essential function in the fresh-
cut produce business. Modified atmosphere packaging (MAP) is a technology
which is used to protect the quality and maintain the shelf life of fresh fruits and

vegetables for longer periods (Moleyar 1994). MAP can help to extend the

103

storage life of fresh-cut produce by manipulating the oxygen (O2) and carbon
dioxide (CO2) mass balances, coordination of the storage temperature and the
permeability of the polymeric film to allow O2 to enter and CO2 to leave.

Before designing the package, it is very important to understand the
product requirements to avoid undesirable physiological damage since each fruit
and vegetable has its own respiration rate and its safe 02 and CO2 headspace
levels. Fresh asparagus has a very high metabolic activity and its tolerance levels
are less than 10% at 3-6°C and less than 15 % at 0-3°C for CO2 concentration,
and less than 10% O2 leads to discoloration (Kader 1989a; Saltveit 1989;
Ooraikul 1991; Kader 1993). The recommended modified atmosphere O2 and
CO2 levels for maintaining the quality attributes of fresh asparagus are 21% O2
(Air) and 5-10% CO2 (Kader 1985).

Vacuum packaging has been used as a method to preserve food since the
1960s, mostly dried foods and meat products (Blakistone 1998). Vacuum
packaging helps to retard aerobic microbial growth, which is a cause of spoilage.
Vacuum skin packaging (VSP) uses the same technique as vacuum packaging,
and in addition uses a themoforrnable film to seal over the product against a rigid
backboard (T ewari 2002). This process has been used to maintain meat product
quality. The use of this technique with fresh asparagus and other fresh produce
is not widely accepted.

In recent years, a permeable polymeric film/pouch has been used as a
package for MAP and vacuum packaging to extend the shelf life of whole/cut

fresh produce. To bring more added values to the fresh asparagus market as

104

well as to meet consumer demand for ready-to-eat products, microwaveable tray
systems are being investigated for ready-to-eat products.

This study has investigated the storage shelf life of fresh-cut green
asparagus packed in MAP and VSP microwaveable tray systems at the
commercial storage condition of 4°C, 80% RH.

4.2 Materials and Methods
4.2.1 Sanitization, packaging and storage

Fresh, green Peru asparagus produced and packed by Danper Trujillo
S.A.C under the brand name CASAVERDE® was used in this research. After one
day of shipment in corrugated boxes with gel-ice packs (2-5°C), the asparagus
was transported to controlled storage rooms (4°C, 80% RH) in the School of
Packaging and Food Science and Human Nutrition building, East Lansing, MI.
Medium diameter (8/16 - 11/16 inch) asparagus spears (US. Department of
Agriculture 1997) were sorted and trimmed to a length of 6 inches. Trimmed
spears were washed with distilled water and deionized distilled water to remove
soil, debris and any other contamination and then sanitized by dipping in a 200
ppm sodium hypochlorite sanitizer (Cleaner and Sanitizer, Johnson® CRS, US)
for 2 minutes (Suslow 1997; Parish ME. 2003) and left for 5 minutes on
perforated trays before washing twice with distilled water. Sanitized spears were
dried with sanitized paper towels before packaging in containers. The pH of the
chloride solution was controlled with vinegar to approximately 5.27 prior to use in
order to increase the activity of the chlorine against pathogens. Fresh-cut

asparagus was packed into microwaveable containers supplied by DuPont

105

Packaging & Industrial Polymers (Wilmington, DE) and Cryovac Sealed Air
Corporation (Duncan, SC). Two types of packaging techniques were used:
modified atmosphere packaging (MAP) and vacuum skin packaging (VSP). Both
tray systems were sealed with highly permeable Iidding films as provided by the
above manufacturers. A Multivac T-200 machine (Multivac, Inc., Kansas City,
MO.) was used to pack the asparagus in both type systems. Products were
stored at 4°C, 80% RH, a commercial storage condition, during the experimental
storage time of 21 days. Asparagus in MAP and VSP trays is shown in Figure 4.1.
Modified AtmospLere Pagkaging (MAP): 226.5 g (0.5 lb) of pre-trimmed spears
were packed in Dupont® microwaveable trays (5% in x 71/2 in x 1‘/2 in,
Polypropylene, Dupont®, Dura Freshm, Wilmington, DE). A passive modified
atmosphere was established with medical air composed of 21% O2, and 0.03 %
C02, The Iidding film from Dupont® (Appeel Lidding Sealant Resin 004, 2.5 mils
thickness, O2 permeability of 7.75 cc.mil/in2.day.atm and CO2 permeability of 8.0
cc.miI/in2.day.atm) was heat sealed using 80 psi to the trays.

Vacuum Skin Packaging (VSP): 135.9 g (0.3 lb) of fresh-cut green asparagus
spears were packed under vacuum in Cryovac® microwaveable trays (4% in x 6%
in x 1% in, C8966-B2, Cryovac®, Simple Steps“, Duncan, SC) and then
vacuum-sealed with a Cryovac® Iidding film (3 mils thickness, O2 permeability of

14.3 cc.millin2.day.atm and CO2 permeability of 59.9 cc.mil/in2.day.atm).

106

 

     

 

   

Dupont® MAP tray 1 Cryovac® VSP tray

Figure 4.1: Fresh-cut green asparagus spears packed in a Dupont® tray using
MAP, and a Cryovac® tray using VSP
4.2.2 Product Evaluation

Product analysis was performed on the stored samples every 3 days by
sampling three trays from each tray system for the parameters mentioned.
Triplicate analyses of each parameter for each of the three trays were done on
the samples. The process used for asparagus is illustrated in Appendix A.
4.2.2.1 Weight loss

The loss of weight is important since it can relate to an economic loss, as
well as loss of quality. Three MAP trays and VSP trays were removed from
storage and weighed to determine the water loss of product over the storage time
using a precision balance scale (Arlington, VA). The weight loss from the product
trays for each evaluation was calculated from the weight average of three
samples of each treatment.
4.2.2.2 Moisture Content

Whole asparagus spears were randomly selected from each tray system

and chopped to a length of 0.5 inch. A sample weight of approximately 11 g was

107

contained in an aluminum pan and dried in a vacuum oven (Precision Scientific,
model 5831, National Appliance Company, Kokomo, IN) at 100°C (212°F) for 4
hours and then reweighed after cooling to determine the loss of weight (AOAC
1984). Moisture content was calculated as “wet basis”, which is expressed as the

loss in weight of asparagus after drying compared to the product fresh weight.

 

_ Initialweight — F inalweight x

WetBasis 100

Initialweight

4.2.2.3 Headspace gas analysis

Oxygen (O2) and carbon dioxide (CO2) concentration in the package
headspace were monitored using an O2/CO2 gas analyzer (Illinois 6600 Head
Space Analyzer, Illinois Instruments, Inc., Johnsburg, IL). To avoid gas exchange
with the surrounding atmosphere during measurement, a septum (septum PPL-
193456, Illinois Instruments, Inc., Johnsburg, IL) was attached to the film surface
of the packages. The MAP package was monitored for O2/CO2 gas using the
automatic sampling mode of the machine while the O2/CO2 gas in the VSP
package was analyzed using a syringe to gather 10 ml of gas from inside the
package. It was then injected in the manual sampling mode of the machine and
the gas composition inside the package was determined.
4.2.2.4 pH analysis

Whole asparagus spears were randomly selected from each package
treatment. Approximately 15 g was blended with 100 ml Milli Q water in a blender.
The pH of the solution was measured using a pH-meter (PHB-212

microprocessor pH meter, Omega Engineering, Inc., CT).

108

4.2.2.5 Microbial analysis

Asparagus spears (25 g) were randomly taken from trays of each
packaging system. Samples were placed into a sterile Whirl-Pack® sampling bag
(6 x 9 inch polyethylene bag, Whirl-Packm, Nasco, Fort Atkinson, WI) and then
homogenized with 100 ml of sterile 0.1% peptone water (Bacto Peptone, DifcoT",
Becton Dickinson and Company, USA) in a stomacher (Seward Stomacher 400
lab system, Seward Medical, London, UK) for 2 minutes at high speed. Serial
dilutions (10", 10°, 10°, 10“ and 105) were made from 1 ml of the
asparagus/fluid mixture with 9 ml of sterile 0.1% peptone water in sterile tubes.
Duplicate samples were plated on the following media as shown below according
to the methods described in APHA (1984), and Villanueva and others (2005).
Plate counts were determined as average values of each serial dilution and
reported as logarithmic values of colony-forming units per gram of asparagus for
each treatment (Log 10 CF U/g). All analyses were done in duplicate.
:1 Total Count Bacteria was determined by spread-plating 50 ul of the diluted
samples on Trypticase Soy Agar or TSAYE-C (Difcom, Becton Dickinson and
Company, USA) containing 0.6% yeast extract and 100 ppm cyclohexamide
(Sigma-Aldrich Co., St. Louis, MO). TSAYE-C plates were counted after 2-3 days
of incubation at 35°C. The countable bacteria were 25-250 total count bacteria
per plate.
a Yeasts and Molds were determined by spread-plating 50 pl of sample solution
on Potato Dextrose Agar or PDA-SA (DifcoTM, Becton Dickinson and Company,

USA) containing 20 ppm streptomycin (Sigma) and 50 ppm ampicillin (Sigma-

109

Aldrich Co., St. Louis, MO). PDA-SA plates were counted after 3-7 days of
incubation at 23°C (room temperature). The countable range of yeast and mold

was 15-150 per plate.

a E. coli and coliforms were determined by spread-plating 1 ml of sample
solution in duplicate on 3M Petri films (3M PetrifilmW, MN). The films were
incubated in chamber at 35°C and the plates examined after 24 hours.

4.2.2.6 Sensory Quality

Sensory evaluation using the human senses was applied to evaluate
product quality (ASTM 1992). Vlsual and organoleptic characteristics of the
samples were monitored to determine consumer acceptability and product shelf
life during the storage time by a 9 member trained panel (Meilgaard 1991).
Panelists were chosen from MSU students who were selected on the basis of
their ability to detect specific product attributes. All panelists participated in the
training which was conducted over a 1‘/z year period. The sensory testing was
conducted in the Sensory Laboratory, Trout Food Science and Human Nutrition
building at Michigan State University (consent form shown in Appendix B).

An evaluation of the visual and organoleptic quality of fresh green
asparagus was conducted using a standard asparagus color and grading scale
which was created to evaluate characteristics of the fresh green asparagus: odor,
stalk color, tip color and texture. The appearance of fresh green asparagus
includes characteristics such as stalk straightness, tenderness and a shiny deep
green stalk, and a green-pink violet color with tightly closed and compact head

tips (Lipton 1990; Michigan Asparagus Advisory Board 2005). Panel training was

110

based on fresh product and unacceptable product (end of the shelf life) in order
to give the panelists a range of attribute intensities.

The quality attribute characteristics included color, odor, texture
(crispness/freshness) and overall appearance. The samples were evaluated
using a 5-point hedonic scale, where 5 represented the best (fresh) and 1 was
the worst (spoiled) as indicated in Appendix C. Statistical analysis of the sensory
data was performed using the statistical software program, SAS version 8.01.

4.3 Results and discussion
4.3.1 Weight Loss

No weight loss of fresh-cut green asparagus stored in MAP and VSP at 4
°C, 80% RH during storage for 21 days was detected. No loss in weight of the
asparagus occurred because of the protection of the plastic Iidding films and the
water barrier nature of the polypropylene (PP) based tray materials.
Polypropylene is a good water vapor barrier.

4.3.2 Moisture Content

The moisture content of product was calculated as wet basis (VVB) and
resulted from the average values of duplicate analyses from three samples of
each treatment. Approximate moisture content of fresh asparagus at the first day
of the experiment, prior to storage (day 0) was 93%. Moisture content of the
products packed in the MAP and VSP systems over a storage time of 21 days at
4 °C, 80% RH remained satisfactory as shown in Table 4.1 and Figure 4.2. The
range of moisture contents of the fresh-cut spears during storage was 93.57% to

93.78% for MAP and 93.48% to 94.03% for VSP. There was a slight increase in

111

moisture content, but this increase was not significant (p>0.05) as compared to
the initial moisture content. This indicates that both polymeric material based
packaging systems successfully maintained the moisture in the asparagus
packages.

Table 4.1: The moisture content of fresh-cut asparagus during storage at 4°C

% Moisture Content (wet basis)

Days
MAP VSP

 

 

 

10000-
H
5
*5 7500-
O
U
E 5000—
.0
O
E 25.00-
.\°

0.00-

 

0 ‘ 3 6 9 12 15 18 21 Days
I MAP-Dupont all VSP-Cryovac

Figure 4.2: Percent moisture content of fresh green asparagus in MAP and VSP
packages at 4°C, 80% RH during 21 days of storage

112

4.3.3 Headspace gas Analysis

The change in respiratory gases inside the headspace of fresh-cut green
asparagus packed under MAP and VSP systems is illustrated in Figure 4.3 for
MAP, Figure 4.4 for VSP and Figure 4.5, for comparison between the two
packaging systems. Concentration of oxygen (O2) and carbon dioxide (CO2)
inside both systems changed during storage. The level of O2 tended to decrease
whereas the CO2 concentration increased. These changes occurred because of
the respiration process of the fresh asparagus and the metabolism of
microorganisms which consume 02 and produce CO2. Gas exchange between
the external and internal atmospheres as mediated by the permeable polymeric
film also affected the headspace gas concentration.

The initial gaseous atmosphere inside the MAP package was air (21% O2
and 0.03% CO2). The O2 level inside the MAP package fell moderately from its
initial value of 20.9% to roughly 17%, and the CO2 level rose substantially from
0.03% to approximately 5%. O2 and CO2 concentrations in the MAP package
reached equilibrium after day 6. Although the VSP technique attempts to
eliminate all air from the package, it is difficult to achieve complete vacuum and
thus remove all of the air from the package. The concentration of O2 and CO2 in
VSP at the beginning was assumed as ideal 0%. The O2 and CO2 concentrations
inside the VSP packages during storage changed opposite to those in MAP. Both
gases rose substantially and equilibrium concentrations of O2 and CO2 were met
after 6 days and 3 days, respectively. The final concentrations of both gases in

MAP and VSP packages were within the threshold of the tolerance limits for fresh

113

asparagus, which are not lower than 10% for O2 to prevent injury and not greater

than 15% for CO2 at a 0-3°C storage temperature (Kader 1989b; 1993; Salveit

1993 ; Thompson 1998).

 

 

 

 

 

 

25
20 c\—#
M
8 15 -
1!
C
§
lg 10-
5 /\._ H“
0 I I I I I I I
0 3 6 9 12 15 18 21 Days

'0- 02, MAP +C02, MAP

Figure 4.3: 02 and CO2 concentrations of fresh-cut asparagus stored in the MAP
at 4°C, 80% RH during 21 days of storage

114

 

25

201

 

Percentage

 

 

 

 

I I T I T I

0 3 6 9 12 15 18 21 Days

 

'0-02, VSP +C02, VSP

Figure 4.4: O2 and CO2 concentrations of fresh-cut asparagus stored in the VSP
system at 4°C, 80% RH during 21 days of storage

 

 

 

 

25

204
o . . . O O O
O 15 1 e
g 0 0 ° .
d) e
2
g 10-

5 1

0 I I I I I I

0 3 6 12 15 18 21 Days

'0'02, MAP +C02, MAP +02, VSP +C02, VSP

Figure 4.5: O2 and CO2 concentration of fresh-cut asparagus stored in the MAP
and VSP system at 4°C, 80% RH during 21 days of storage

115

4.3.4 pH Analysis

The pH values of fresh-cut asparagus products packed in both systems
decreased after 9 days of storage, and decreased to levels of 6.04 for MAP
asparagus and 5.98 for VSP product after 21 days as indicated in Table 4.2 and
Figure 4.6. However, there was no significant difference (p>0.05) between the pH
of product packed under MAP and VSP during the experimental time.

Table 4.2: The pH values of fresh asparagus in MAP and VSP stored at 4°C,
80% RH for 21 days of storage

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Average pH
Day MAP VSP
0 6.111002 6.111002
3 6.121003 6.131011
6 62710.02 6.241010
9 5.961007 5.971006
12 5.891006 5.921002
15 6.121005 5.881016
18 5.861013 6.131015
21 60410.13 5.981029
8.00
E 4.00 -
0.00 I I T l I I I

 

 

 

0 3 6 9 12 15 18 21 Days

'0- MAP +VSP

Figure 4.6: The pH measurement of fresh-cut asparagus in MAP and VSP at 4°C,
80% RH during 21 days of storage

116

4.3.5 Microbial Analysis

The mix of microorganisms on the asparagus included bacteria, yeasts
and molds and are commonly found on many fresh fruits and vegetables.
Contamination of fresh vegetables by pathogens and spoilage microorganisms
originally occurs in the field during harvesting, handling, processing, packing and
distribution. The original microbial population on fresh produce is generally high
and depends upon the types and the physiological condition of the fresh produce
(Zagory 1999). The population of bacteria initially on fresh-cut asparagus before
washing with 200 ppm sodium hypochlorite was 5.65 logio CFU/g and yeast was
5.44 Iog1o CFU/g. After sanitizing, the initial bacteria load and yeast on day 0
(prior to storage) were reduced to 4.75 log1o CFU/g and 3.08 log1o CFU/g,
respectively. This shows that washing asparagus with sodium hypochlorite
solution can help to reduce the initial microbial load about 1 to 2 log which is
similar to that reported by Cherry (1999) and Parish (2003).

The microbial population of packed fresh-cut asparagus in MAP and VSP
tray systems increased significantly over storage as shown in Figure 4.7 for
bacteria, and Figure 4.8 for yeasts. At the end of the experiment (day 21), the
microbial growth of product stored under MAP at 4°C was approximately 7.61
log1o CFU/g for aerobic bacteria, and 7.21 log1o CF U/g for yeast and molds. The
population of collforrns was 2.34 10910 CFU/g as shown in Table 4.3. The growth
of total aerobic bacteria in the VSP package at 4 °C was 7.79 Ioglo CF U/g on day
21 while the yeast and mold count was 7.33 10910 CFU/g. Coliforms was not

detected (Table 4.3).

117

 

The microbial growth on fresh-cut asparagus in the MAP package was
slightly lower than for that stored in the VSP package. The bacteria population in
the modified atmosphere-packed asparagus was very similar to that reported by
Berrang (1990) and Osuna (1995) at 2°C, 80% RH at the initial time point (day 0)
after sanitizing and after 21 storage days. There was no significant difference in
microbial growth on fresh-cut asparagus packed in MAP and VSP systems
(p>0.05).

Table 4.3: Microbial populations on fresh-cut asparagus stored in MAP and VSP
at 4°C, 80% RH during storage

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Microbial Quantity (L091o CPU/g)
Sample Days “82:12:; N Yeast and molds Coliforms
0 (unwashed) 5.671033 5.361031 00010.00
0 (washed) 4.661039 2.881061 0.001000
3 5.121089 45611.57 07711.33
6 6.351048 5.971045 00010.00
MAP 4°C 9 5.8311.70 5.4912.10 08011.38
12 7.091058 6.961073 12911.14
15 7.731015 70610.39 09111.58
18 7.951038 7.111069 08511.47
21 7.501043 7.151026 09411.62
0 (unwasheQ 5.591029 5.361031 0.001000
0 (washed) 4.661039 2.881061 0.001000
3 50311.12 4.861129 0.731126
6 5.931020 5.761034 00010.00
VSP 4°C 9 60211.13 65411.13 0.001000
12 7.191021 6.941033 0.571098
15 70911.10 70610.89 0.001000
18 7.381089 7.151096 1.681146
21 7.751025 7.331006 0.571098

 

118

 

Total count bacteria

 

10

 

 

 

 

 

’2"

D

u.

0

o:

o

d

E

:1

o

0

2

8 2 -

S
O I I I I I I I I
0 0 3 6 9 12 15 18 21 Days

(Unwashed) (Washed)

-0- MAP 4°C +VSP 4°C
Figure 4.7: The population of total count bacteria on fresh-cut asparagus stored
in MAP and VSP at 4°C, 80% RH during 21 days of storage

Yeast and Molds

 

 

 

 

 

10
‘27
D
u.
0
c»
o
:1
E
:1
o
o
o
‘5
«1
5
O I r I I I I I I
0 0 3 6 9 12 15 18 21 Days
(Unwashed) (Washed)

-0- MAP 4°c +vs1= 4°c

Figure 4.8: The yeast and mold population on fresh-cut asparagus stored in MAP
and VSP at 4°C, 80% RH during 21 days of storage

119

4.3.6 Sensory Quality

The sensory analysis results are illustrated in Table 4.4 and Figure 4.9.
The shelf life of the product was determined by acceptability of the overall
appearance of the asparagus. Sensory quality of fresh-cut green asparagus
stored under MAP at 4°C, 80% RH, including odor, tip color, stalk color, texture
and overall appearance was shown to be acceptable at 21 days.

F resh-cut asparagus in VSP packages at the same storage conditions had
a product shelf life of approximately 18 days. Unpleasant odor (musty odor), tip
color change and degradation of the stalk green color were observed on day 21.

Table 4.4: Panelist’s response (mean) for fresh-cut asparagus stored in MAP and
VSP at 4°C, 80% RH

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Color Overall
Sample Days Stalk Tip Texture Odor Quality
0 5.0 ° 4.9 ° 4.9 ° 5.0 ° 5.0 °
3 4.8 4.7 4.9 4.9 5.0
6 4.8 4.9 4.9 5.0 4.9
. 9 4.8 5.0 4.9 4.9 5.0
MAP4 C 12 4.4 ° 432’ 4.7 4.6 ° 4.4 °
15 4.4 ° 4.3 ° 4.8 4.3 ° 4.4 °
18 4.0 ° 4.0 ° 4.0 ° 4.0 ° 40°
21 3.6 ° 3.8 ° 3.7 ° 3.4 ° 3.4V
0 5.0 ° 4.9 ° 4.9 ° 5.0 ° 5.0 °
3 4.9 4.8 4.9 4.9 4.9
6 4.9 4.8 4.9 5.0 5.0
.- 9 4.8 4.6 4.7 5.0 4.8
VSP4 C 12 4.1 ° 4.1 ° 4.4 4.4 4.6 °
15 4.1 ° 4.3 ° 4.3 ° 4.7 4.3 °
18 3.2 ° 3.2 ° 3.8 ° 3.8 ° 3.2 °
21 2.7 ° 3.0 ° 3.2 ° 3.0 ° 2.1 °

 

 

 

 

 

 

 

 

a” Means within a column, which are not followed by a common superscript letter,
are significant difference (p<0.05).

120

 

 

 

Stalk color Tip color Texture

 

 

 

5'..00 5‘0.0: . 5‘eeeg‘:

.. :z. .. c .
’ 3

3- . 31 .03-

 

 

 

 

 

I I I I I r I I I I I

1 I II [III IIII
36912151821 036912151821 036912151821

 

 

 

 

Average Score
0

 

 

 

 

 

 

 

 

 

 

Odor Overall quality
510 . O . 510 O . t
0 3 0 o
4' 3 41 O PKG
e e
e VSP4C
2‘ 21 .
1‘ I l T F I T F I 1J I I I I I I I I
036912151821 036912151821
Days

Figure 4.9: The sensory quality of fresh-cut asparagus packed in MAP and VSP
trays at 4°C, 80% RH during 21 days of storage

4.4 Conclusion

The VSP system was successfully used to prolong the shelf life of fresh-
cut green asparagus at 4°C, 80% RH for 18 days while a passive MAP system
maintained the freshness and extended the shelf life of fresh asparagus though
21 days. There was no significant difference in weight loss, moisture content
(93% same as the fresh sample at the initial day), pH and the microbial
population between asparagus in either packaging system during storage for 21
days.

The initial physiological condition of fresh vegetables, proper handling and
sanitation techniques and packaging system can extend product shelf life by
affecting both microbial load and chemical degradation. Systems which lead to

the proper proportion of gases inside the package can also maintain shelf life.

121

 

The appropriate film permeability, film thickness, and film surface area along with
storage temperature can successfully preserve product quality, eliminate/control

microbial growth and delay overall product deterioration.

122

 

4.5 Bibliography

AOAC. 1984. Official Methods of Analysis. Association of Official Analytical
Chemists, editor. Virginia.

APHA. 1984. Compendium of Methods for the Microbiological Examination of
Foods.2
ed. District of Columbia: American Public Health Association.

ASTM. 1992. MNL 14. The Role of Sensory Analysis in Quality Control

Berrang ME, Brackett, RE. and Beuchat, L.R. . 1990. Microbial, color and
textural qualities of fresh asparagus, broccoli, and cauliflowers
stored under controlled atmosphere. Journal of Food Protect 53:391-5.

Blakistone BA. 1998. Principles and applications of modified atmosphere
packaging of food. 2 ed: Blackie Academic & Professional, an imprint of
Thomson Science. 1-38, 123-34 p.

Cherry JP. 1999. Improving the safety of fresh produce wtih antimicrobials. Food
Technology 53(1 1):54-9.

Esteve MJ, Farre, R. and Frigola, A. 1995. Changes in ascorbic acid content of
green asparagus during the harvesting period and storage. Journal of
Agric Food Chem 43:2058-61

Fallik E, Aharoni, Y. 2004. Postharvest physiology. Pathology and Handling of
fresh produce.

Hexamer FM. 1901. Asparagus, its culture for home use and for market; a
practical treatise on the planting, cultivation, harvesting, marketing, and
preserving of asparagus, with notes on its history and botany. New York:
Orange Judd Company. 1-4, 83—99 p.

IFPA. 2003 Flexible packaging material basics. In: Gorny JR, editor. Packaging
design for fresh-cut produce: International F resh-cut Produce Association.
p 1-3.

Kader AA. 1986. Biochemical and physiological basis for effects of controlled and
modified atmospheres on fruits and vegetables. Food Technology
40(5):99-104.

Kader AA. A summary of CA requirements and recommendations for fruit other
than pome fruits; 19898; Wenatchee, Washing ton USA.14-16 June 1989.
Other Commodities and Storage Recommendations. p 303-28.

Kader AA. Postharvest biology and technology; 1992 University of California.

123

Kader AA. Modified and controlled atmosphere storage of tropical fruits; 1993;
Proceeding of an International Conference, Chiang Mai, Thailand. 19-23
July 1993. p 239-49.

Kader AA, Zagory, D., Kerbel, E.L. . 1989b. Modified atmosphere packaging of
fruits and vegetables. CRC Crit Rev Food Sci 28(1):1-30.

Lipton WJ. 1990. Postharvest biology of fresh asparagus. Hort Rev 12:69-155.

Luo Y, Suslow, T., Cantwell, M., United States Department of Agriculture-
Agricultural Research Service USDA-ARS. 2006. Asparagus.

Meilgaard M, Civille, G.V., Carr, B.T. 1991. Sensory evaluation techniques. 2 ed.
Boca Raton, FL.: CRC Press, Inc. 187—211 p.

Michigan Asparagus Advisory Board. 2005. Questions about Asparagus.

Moleyar V, Narasimham, P. 1994. Modified atmosphere packaging of vegetables:
an appraisal. Journal of Food Sci Technol 31(4):267-78.

Ooraikul B, Stiles, ME. 1991. Modified Atmosphere Packaging of Food. Watson
DH, editor. New York: Ellis Harwood Limited. 147,170-227 p.

Osuna JJ, Zurera, G., Garcia, RM. 1995. Microbial growth in packaged fresh
asparagus. Journal of Food Quality 18 203-14.

Parish M.E. B, L.R., Suslow, T.V., Harris, L.J., Garrett, E.H., Farber, J.N., Busta,
F .F . 2003. Method to reduce/eliminate pathogens from fresh and fresh-cut
produce. Comprehensive reviews in food science and food safety. p 161-
73.

Parish ME, Beuchat, L.R., Suslow, T.V., Harris, L.J., Garrett, E.H., Farber, J.N.,
Busta, PF. 2003. Method to reduce/eliminate pathogens from fresh and
fresh-cut produce. Comprehensive reviews in food science and food
safety. p 161-73.

Peirce LC. 1987. Vegetables: Characteristics, production, and marketing. New
York: Wiley. 173-83 p.

Rubatzky VE, Yamaguchi, M. 1997. World Vegetables. Principles, Production
and Nutritive Values. 2 ed: Chapman & Hall. 645-57,802 p.

Saltveit ME. A summary of requirements and recommendations for the controlled
and modified atmosphere sotrage of harvested vegetables; 1989;
Wenatchee, Washington, USA. Other Commodities and Storage
Recommendations. p 329-52.

124

Salveit ME. 1993 A Sumary of CA and MA requirements and recommendations
for the storage of fruits and vegetables. Proceedings of sixth international
controlled atmosphere research conference. Ithaca, NY.

Suslow TV. 1997. Postharvest Chlorination: Basis properties and key points for
effective disinfection. Resources Publication 8003.

Tewari G. 2002. Microbial control by packaging. In: Vijay K. J, V.K., Sofos, J.N. ,
editor. Control of foodborne microorganisms. New York Marcel Dekker. p
191-208.

Thompson AK. 1998. Controlled Atmosphere Storage of Fruits and Vegetables. 1
ed. Oxon ; New York: CAB International. 81-116 p.

US. Department of Agriculture. 1997. United States standards for grads of fresh
asparagus.

Villanueva MJ, Tenorio MD, Sagardoy M, Redondo A, Saco MD. 2005. Physical,
chemical, histological and microbiological changes in fresh green
asparagus (Asparagus officinalis, L.) stored in modified atmosphere
packaging. Food Chemistry 91(4):609-19.

Zagory D. 1999. Effect of post-processing handling and packaging on microbial
populations. Postharvest Biology Technology 15 (3):313—21 .

125

5 SENSORY QUALITY OF COOKED READY-TO-EAT FRESH ASPARAGUS
BY MICROWAVEABLE MAP AND VSP TRAY SYSTEMS
Abstract

Fresh-cut produce, as a ready-to-eat product has become an increasingly
popular product and is successful in today’s market due to the consumer’s desire
for convenience, a nutritionally well-balanced diet and tasteful food. Unlike other
food products, fresh-cut produce continues to respire even after harvesting.
Asparagus (Asparagus officinalis L.) is one of the most consumed vegetables
worldwide and has a very high metabolic rate. The shelf life of fresh asparagus
as a ready-to-eat product can be prolonged by the use of modified atmosphere
packaging (MAP) and/or vacuum skin packaging (VSP) in microwaveable
containers. This can help to preserve the quality and enhance the shelf life of
fresh-cut asparagus, as well as increase the ease of cooking.

Fresh-cut asparagus was packed in microwaveable MAP and VSP
systems at a commercial storage temperature and cooked “in tray containers”
using a microwave oven and several microwave time and power level
combinations. Quality of the cooked asparagus in the microwaveable MAP and
VSP tray systems was sensorially evaluated at several cooking times and
microwave power levels. Preference of packaging type (MAP and VSP) was also
determined. Cooking time and microwave power level affected the quality of the
cooked asparagus, 2 - 3 minutes at full (100%) power for MAP and 2 minutes at
medium (50%) power for VSP were found to produce a satisfactory product in the

microwavable tray systems based on sensory evaluation. The preference for

126

 

packaging types test showed that slightly more than half of the consumer
panelists preferred the MAP package to the VSP package. However, there was

no significant difference (p>0.05) in the preference of packaging type.

5.1 Introduction

Fresh-cut produce is a rapidly growing element in the diet of many
individuals, resulting in the continuous development of these products by the
food industry. The fresh-cut fruit and vegetable business has been a large-scale
success due to the demand trends of today’s consumer, and their concerns for a
healthy diet, functional nutrition and convenience (Garrett 2002).

Asparagus (Asparagus officinalis L.) is a perennial crop of the lily
(Liliaceae) family (Hexamer 1901; Peirce 1987). It is a nutritionally well-balanced
vegetable. Asparagus is composed of fibers and abundant essential nutrients
such as vitamin A, vitamin B, vitamin C, folate, potassium, copper, zinc and
carotenoids (California Asparagus Commission 2007). There are several
asparagus varieties such as green, white and purple. Green asparagus is the
most popular edible form in today’s market, especially in the United States,
Japan, New Zealand, Australia, Chile and the European market (Esteve and
others 1995; Luo and others 2006). Asparagus is a crop that can be processed
and marketed as a fresh-cut product thereby increasing its value.

Like other fresh fruits and vegetables, fresh-cut asparagus respires even
after harvest. Asparagus has a high post-harvest respiration rate (>60 mg
COleg-hr) that makes it a highly perishable vegetable (Kader 1986; Kader 1992 ;

Fallik and Aharoni 2004). Extending the shelf life of fresh-cut asparagus is very

127

important in increasing its economic viability. Packaging is very important for
fresh-cut asparagus not only to serve today’s consumer demand for convenience
and time saving as a ready-to-cook/eat product, but also to allow the product to
continue the respiration process, thus preserving its product quality through shelf
life extension techniques. Modified atmosphere packaging (MAP) is an especially
useful packaging technique which can reduce water loss, slow ethylene
biosynthesis and microbial growth (Gorny 1997). MAP uses a gas mixture and
permeable polymeric films to decelerate respiration and slow down the
senescence of the product. It has been shown that MAP can help to maintain the
quality and shelf life of many fresh fruits and vegetables such as broccoli and
asparagus (Lange 2000). Vacuum skin packaging (VSP) is another technique
which can help to preserve food quality and retard the growth of microorganisms
by first pulling a vacuum on the packaged product, and then a polymeric film is
vacuum-sealed over the product against a rigid backboard (Tewari 2002).

The microwave oven has become a handy kitchen appliance for cooking
or heating food quickly. The use of microwaveable containers, therefore, creates
the possibility for value-addition to the fresh-cut asparagus by increasing the
ease of food preparation.

The main objectives of this study were to develop value added fresh-cut
asparagus as a ready-to-eat product, and to determine the cooked quality of

fresh asparagus using sensory evaluation.

128

 

5.2 Materials and Methods
5.2.1 Sanitation and packing

Fresh, green Peruvian asparagus was used in this experiment, and was
produced and packed by Danper Trujillo S.A.C under the brand name
CASAVERDE®. Medium diameter (8/16 - 11/16 inch) asparagus spears (US.
Department of Agriculture 1997) were sorted and cut into a length of 6 inches.
Cut spears were washed with distilled water and then deionized distilled water to
remove any contamination. 200 ppm sodium hypochlorite sanitizer (Cleaner and
Sanitizer, Johnson® CRS, US) was used with vinegar to control the pH of the
chloride solution to approximately 5.27 prior to use. This was done in order to
activate the chlorine against pathogens (Suslow 1997; Parish and others 2003).
This solution was used to sanitize asparagus by dipping for 2 minutes and then
the asparagus was left for 5 minutes before washing twice with distilled water.
Sanitized spears were dried with sanitized paper toweling before packaging in
microwaveable containers supplied by DuPont Packaging & Industrial Polymers
(Wilmington, DE) and Cryovac Sealed Air Corporation (Duncan, SC).

226.5 g (0.5 lb) of pre-cut asparagus were packed in Dupont®
microwaveable trays (51/4 in x 71/2 in x 1‘/2 in, Polypropylene, Dupont®, Dura
Fresh”, Wilmington, DE). A passive modified atmosphere was established with
medical air composed of 21% Oz, and 0.03 % C02 and heat—sealed using a
Iidding film from Dupont®(Appeel Lidding Sealant Resin 004, 2.5 mils thickness,
02 permeability of 7.75 cc.mil/in2.day.atm and 002 permeability of 8.0

cc.miI/in2.day.atm). For vacuum skin packaging (VSP), 135.9 g (0.3 lb) of spears

129

were packed in Cryovac® microwaveable trays (4% in x 6% in x 1% in, C8966-82,
Cryovac®, Simple Steps“, Duncan, SC) and then vacuum-sealed using a
Cryovac®lidding film (3 mils thickness, 02 permeability of 14.3 cc.miI/in2.day.atm
and C02 permeability of 59.9 cc.mil/in2.day.atm). Both systems were packed
using a Multivac T-200 machine (Multivac, Inc., Kansas City, MO). Products were
then stored for 1 day at 4°C, 80% RH, prior to use. The MAP and VSP packages
are shown in Figure 5.1.

5.2.2 Cooking and Sensory Evaluation

After one day storage, asparagus packages were cooked “in package”
using a 1.5 KW GE microwave (GE® Countertop Microwave Oven, General
Electric Company, Louisville, KY). For MAP packages, the Iidding film was
removed or holes by fork were made in it before cooking for 2 and 3 minutes at
full (100%) power. For the VSP package, products were cooked without peeling
the film off, for 2 minutes at full (100%) power and 2 minutes at medium (50%)
power. All microwave cooking conditions were selected from a preliminary test (1
minute at high power, 2 minutes at high power, 2 minutes at medium power and
3 minute at high power) based on trained panel data.

A consumer sensory panel evaluated the quality attributes of the cooked
asparagus. The 80 panelists were recruited from MSU faculty and students of
both sexes between the ages of 20 and 60 years old and who consumed fresh
asparagus (consent form shown in Appendix D). After microwave cooking, two
asparagus spears were randomly selected from each package treatment (MAP

and VSP), and the different cooking conditions and served in an aluminum foil

130

wrap with a specific 3 digit random code as shown in Figure 5.2. Panelists were
asked to sample the whole spears and evaluate several quality attributes of
cooked asparagus including aroma, appearance/color, flavor, texture and overall
acceptability using a 9-point hedonic scale (1 = dislike extremely and 9 = like
extremely) as illustrated in Appendix E. They were also asked to state their
preference, based on product appearance for the asparagus packed in the two
different packing systems (MAP and VSP). ANOVA was used for the statistical

analysis of all sensory attributes. The statistical software was SAS version 8.01.

      

Dupont® MAP tray Cryovac® VSP tray

Figure 5.1: Fresh-cut Michigan asparagus spears packed in a Dupont®tray using
a MAP technique and a Cryovac®tray using a VSP technique

131

  
  

 

\‘ .
_._. ‘ _... » ;:
—-..—1 —. a.

-—..- Mfg-w, -

 

Cooked asparagus in VSP tray

 

Sample of cooked asparagus

Figure 5.2: Microwave cooking of fresh-cut asparagus in MAP and VSP trays and
the cooked asparagus sample presented to the panelists
5.3 Results and Discussion
5.3.1 Modified atmosphere packaging (MAP) tray system

The sensory data for the microwave cooked asparagus shows that there
was no significant difference in the quality attributes (aroma, color, flavor, texture
and overall acceptability) between the cooked asparagus in microwaveable MAP
trays subjected to 2 minutes and 3 minutes at full (100%) power, (Table 5.1).
More panelists gave higher flavor, texture and overall quality scores for
microwave cooked spears for 2 minutes at full power. More panelists liking

aroma as shown in Figure 5.3 for asparagus cooked for 3 minutes at full power.

132

No difference was found for the color at either cooking condition. Slightly more
than half of the consumer panelists (45 of 80) preferred the quality of the
microwave cooked asparagus (2 minutes at full power) as indicated in Table 5.2
and Figure 5.4.

Table 5.1: Sensory quality of the cooked asparagus in the microwaveable MAP
tray

 

 

 

 

 

 

 

 

 

 

. . . Si nificant
Attribute 2 min/Full power 3 min/Full power Digfer en c e
Aroma 7.05 :t 1.45 7.32 i 1.21 NS
Color 7.62 i 1.06 7.64 :l: 1.15 NS
Flavor 6.91 d: 1.44 6.80 i 1.65 NS
Texture 7.12 :t 1.45 6.67 i 1.82 NS
Overall Acceptability 6.96 i 1.40 6.84 :l: 1.61 NS

 

 

*means significant difference (P s 0.01), "means significant difference (P s 0.05)
and NS means no significant difference

Amma

Overall acceptability 4

 

 

Texture " If ’ ‘ X‘SFlavor
+MAP: 2 minlfull power -I - MAP: 3 minlfull power

Figure 5.3: Spider plot of the sensory evaluation of microwave cooked asparagus
in MAP trays under 2 different cooking conditions

133

Table 5.2: Consumer preference for cooked asparagus in microwaveable MAP
trays at 2 different cooking conditions

 

Samples Rank Percent (%) Frequency

2 minutes/full power 1 55.6 45
3 minutes/full power 2 44.4 35

/ 55.6
I

 

 

 

 

 

 

 

 

 

  
 
 
 
 
 
 
 
 
 
 
 
 

606

50*

40a

30a

Percentage

20*

 

10%

 

0%

MAP: 2 min/full power MAP: 3 min/full power

Figure 5.4: Consumer preference for cooked asparagus in microwaveable MAP
trays

5.3.2 Vacuum Skin packaging (VSP) tray system

Based on consumer sensory data, it was found that there was significant
difference between the color and flavor of cooked asparagus in the
microwaveable VSP tray system, 2 minutes at full power versus 2 minutes at
medium power as shown in Table 5.3. The spider chart in Figure 5.5 shows that
the color and flavor of asparagus, cooked for 2 minutes at full power, was more
acceptable to the panelists than the asparagus cooked for 2 minutes at medium

power. The aroma and texture of the cooked asparagus, 2 minute at full power,

134

was also slightly more preferred than that for 2 minute at medium power.
However, there was no significant difference in overall acceptability between
cooked asparagus subjected to the 2 different conditions. Approximately 53.8%
of the consumers liked the asparagus that was cooked for 2 minutes at full power
while only 46.3% preferred the asparagus cooked for 2 minutes at medium power
as indicated in Table 5.4 and Figure 5.6.

Table 5.3: Sensory quality of cooked asparagus in the microwaveable VSP trays

 

 

 

 

 

 

 

Attribute 2mianulI power 2 min! Medium 3.33233:
Aroma 6.61 i 1.65 6.40 i 1.49 NS
Color 7.45 i 1.03 a 7.05 i 1.29 b **
Flavor 6.24 i 1.76 a 5.44 .1: 1.96 D W
Texture 6.15 i 1.71 6.10 i 1.99 NS
Overall Acceptability 6.10 i 1.60 5.68 i 1.93 NS

 

 

 

 

 

*means significant difference (P :<. 0.01), "means significant difference (P s 0.05)
and NS means no significant difference

Amma

 

Overall Acceptability +4..\ Color

 

 

Texture ' * \IFlavor

+VSP: 2 minlfull power -0 -VSP: 2 min/medium power

Figure 5.5: Spider plot of the sensory evaluation of microwave cooked asparagus
in VSP trays under 2 different cooking conditions

135

Table 5.4: Consumer preference for cooked asparagus in microwaveable VSP
trays at 2 different cooking conditions

 

 

 

Samples Rank Percent (%) Frequency
2 minutes/full power 1 53.8 43
2 minutes/medium power 2 46.3 37

 

 

 

 

 

 

Percentage

 

 

 

 

VSP: 2 min/full power VSP: 2 min/medium power

Figure 5.6: Consumer preference for cooked asparagus in microwaveable VSP
trays

5.3.3 Packaging preference of fresh-cut asparagus

Slightly more than half of the consumer panelists (42 of 80) preferred the
appearance of microwaveable MAP packed asparagus as shown in Table 5.5
and Figure 5.7. However, there was no statistical significance in their preference
for the appearance of fresh-cut green asparagus in the two packaging systems

(MAP and VSP).

136

From the demographic questionnaire, it was concluded that for most
consumers the big purchase question is the price and quality (fresh appearance)
of the product. An attractive and convenient package also influences the
consumer buying decision.

Table 5.5: Consumer preference for MAP and VSP packages of fresh-cut
asparagus

 

 

 

Samples Rank Percent (%) Frequency
MAP 1 52.5 42
VSP 2 47.5 38

 

 

 

 

 

 

 

 

 

Percentage

 

 

MAP VSP

Figure 5.7: Consumer preference for overall appearance of fresh-cut asparagus
packed in microwaveable MAP and microwaveable VSP trays

137

5.4 Conclusion

Microwave cooking time and power level affected the quality (aroma, color,
flavor, texture and overall acceptability) of the cooked asparagus. Cooking of
fresh-cut asparagus in a microwavable MAP tray system for 2 - 3 minutes at full
(100%) power was found to produce satisfactory products. Either 2 or 3 minutes
at full power were satisfactory microwave cooking processes for the MAP product.
In the microwaveable VSP tray system, consumers preferred the color and flavor
of cooked spears subjected to 2 minutes at full (100%) power over the 2 minutes
at medium (50%) power. However, there was no significant difference in overall
acceptability between the microwave cooked asparagus from these two different
conditions. Based on the sensory analysis of overall appearance, slightly more
than half of the panelists preferred the appearance of fresh-cut asparagus
contained in modified atmosphere packaging (MAP) to the vacuum skin

packaged (VSP) asparagus.

138

 

5.5 Bibliography

California Asparagus Commission. 2007. Consumer information. National
information.

Esteve MJ, Farre R, Frigola A. 1995. Changes in ascorbic acid content of green
asparagus during the harvesting period and storage. Journal of Agric Food
Chem 43:2058-61

Fallik E, Aharoni Y. 2004. Postharvest physiology. Pathology and Handling of
fresh produce.

Garrett H. 2002. Fresh-cut produce: tracks and trends. In: Lamikanra O, editor.
Fresh-cut fruits and vegetables: science, technology, and market. Boca
Raton: CRC Press. p 1-10.

Gorny JR. 1997. A summary of CA and MA requirements and recommendations
for fresh cut (minimally processed) fruits and vegetables CA 1997
Proceeding Fresh-cut fruits and vegetables and MAP. University of
California: Postharvest Hort.

Hexamer FM. 1901. Asparagus, its culture for home use and for market; a
practical treatise on the planting, cultivation, harvesting, marketing, and
preserving of asparagus, with notes on its history and botany. New York:
Orange Judd Company. 1-4, 83-99 p.

Kader AA. 1986. Biochemical and physiological basis for effects of controlled and
modified atmospheres on fruits and vegetables. Food Technology
40(5):99-104.

Kader AA. Postharvest biology and technology; 1992 University of California.

Lange DL. 2000. New film technologies for horticultural commodities Hort
Technology 10(3):487-90.

Luo Y, Suslow T, Cantwell M. 2006. Asparagus. United States Department of
Agriculture-Agricultural Research Service (USDA-ARS).

Parish ME, Beuchat LR, Suslow TVH, L.J., Garrett EH, Farber JN, Busta FF.
2003. Method to reduce/eliminate pathogens from fresh and fresh-cut
produce. Comprehensive reviews in food science and food safety. p 161-
73.

Peirce LC. 1987. Vegetables: Characteristics, production, and marketing. New
York: Wiley. 173-83 p.

139

Suslow TV. 1997. Postharvest Chlorination: Basis properties and key points for
effective disinfection. Resources Publication 8003.

Tewari G. 2002. Microbial control by packaging. In: Vijay K, Juneja VK, Sofos JN,
editors. Control of foodborne microorganisms. New York Marcel Dekker. p
191-208.

US. Department of Agriculture. 1997. United States standards for grads of fresh
asparagus.

140

CONCLUSION

Modified atmosphere packaging (MAP) and vacuum skin packaging (VSP)
can indeed help to maintain the fresh quality of fresh-cut green asparagus.
Sensory shelf life of fresh-cut asparagus sanitized with 100 ppm sodium
hypochlorite solution showed that MAP can maintain the freshness of fresh-cut
asparagus stored at 1°C and 8°C for 18 days, which is longer than that for VSP
at 1°C and 8°C, (9 days and 3 days, respectively).

The shelf life of fresh-cut asparagus, which was sanitized with 200 ppm
sodium hypochlorite solution; controlled to a pH of 5.27, and stored under MAP
at 4°C was 21 days or more while that stored under VSP was 18 days. There
was no significant difference (p>0.05) in weight loss, moisture content, pH and
microbial growth between fresh-cut spears in MAP and VSP systems during the
entire experimental storage time of 21 days.

The studies also found that the initial quality of fresh produce and a proper
sanitation technique affected the quality and shelf life of fresh-cut asparagus as
well as initial microbial load. In using VSP with fresh-cut asparagus there is
concern about the pressure involved in creating the vacuum to avoid bruising and
causing product damage that can lead to accelerated product deterioration.

Microwave cooking time and power level affected the cooked asparagus
quality (aroma, color, flavor, texture and overall acceptability). The cooked quality
of fresh-cut asparagus packed and cooked in a microwavable MAP tray system
for 2 and 3 minutes at full (100%) power was found to produce a satisfactory

product and these times were not significantly different (p>0.05). For the

141

microwaveable VSP package, there was no significant difference (p>0.05)
between the overall acceptability of the quality of the microwave cooked spears,
2 minutes at full (100%) power, vs. 2 minutes at medium (50%) power. The
consumers, however, preferred the color and flavor of cooked asparagus for 2
minutes at full (100%) power to that of 2 minutes at medium (50%) power.

Slightly more than half of the consumer panelists preferred the
appearance of fresh-cut asparagus packed in modified atmosphere packaging
(MAP) to the vacuum skin packaged (VSP) asparagus. However, there was no
statistically significant difference (p>0.05).

MAP and VSP could help the processors market the fresh-cut vegetables
by extending product shelf life. Use of a microwaveable package with MAP and
VSP techniques can also add value to the product as a ready-to-eat/cook menu

item.

142

 

APPENDICES

143

APPENDIX A

FLOW CHART OF OVER ALL PROCESS

 

144

APPENDIX B

CONSENT FORM FOR SENSORY EVALUATION OF FRESH ASPARAGUS

Department of School of Packaging and Food Science and Human Nutrition,
Michigan State University

Trained Panel Consent Form
Improving Asparagus Quality

Department of School of Packaging and Food Science and Human Nutrition,
Michigan State University

Sample: Asparagus

Before you decide to sign this consent form and continue to participate in our
study, please read carefully and thoroughly the reverse side of this form for the
sample ingredients and preparation information, purpose and procedure of this
study, potential risks and benefits from your participation, our assurance of your
privacy, your rights as a human subject in our study, etc. You must be 18 or older
to participate in this study."

If you have any question during your reading this consent form, or during or after
your participation, please do not hesitate to contact the on-site sensory
evaluation leader and/or the principle investigator. Feel free to contact Dr. Bruce
and Janice Harte, the principle investigator of this study, via phone at 517-355-
4555 or 517-355-8474, ext. 105 (114 Trout Food Science and Human Nutrition
Building, Michigan State University, East Lansing, MI 48823). You also can
reach us via email at harte@msu.edu or harteia@msu.edu for any inquiry you
might have due to your participation in our study.

In case you have questions or concerns about your role and rights as a research
participant, please feel free to contact Bruce Harte, Ph.D., Professor of School of
Packaging, (517) 355-4555, e-mail harte@msu.edu, mail 130 Packaging building,
Michigan State University, East Lansing, MI 48824. If you have read all the
information we offer to you in this consent form and decide to participate in our
study and give us your valuable response to our questionnaire, you can go
ahead and sign this form now. Othenrvise, you can stop here and feel free to
discontinue participation in our study without any penalty.

145

PLEASE NOTE UPON YOUR SIGNING THIS CONSENT FORM, YOU
VOLUNTARILY AGREE TO PARTICIPATE IN OUR STUDY. YOUR
SIGNATURE INDICATES YOU HAVE READ THE INFORMATION PROVIDED
ABOVE AND THAT YOU HAVE HAD AN ADEQUATE OPPORTUNITY TO
DISCUSS THIS STUDY WITH THE PRINCIPLE INVESTIGATOR AND HAVE
HAD ALL YOUR QUESTIONS ANSWERED TO YOUR SATISFACTION. YOU
WILL BE GIVEN A COPY OF THIS CONSENT FORM WITH YOUR
SIGNATURE FOR YOUR RECORDS UPON YOUR REQUEST.

SIGNED DATE

 

146

INVITATIOIN TO PARTICIPATE
You are invited to participate in this study that assesses the quality attributes of
asparagus.

PURPOSE OF THIS STQQY

This study is intended to study the quality consumer and acceptability of
asparagus packed in microwaveable containers. Texture, color, flavor, odor and
overall appearance characteristics of asparagus will be evaluated.

PROCEDURE OF THIS SEDY

Each participant will be presented with asparagus. They will be asked to
evaluate after looking the appearance, score the attributes as presented on the
score sheet for each sample. Samples will be presented using three digit
random codes. We are asking that panelists participate in a quality study of
asparagus. Evaluations should last about 30 minutes or less.

SAMPLE PREPARATION
All the ingredients used in our samples are food-grade and FDA approved for
foods. The ingredients are fresh asparagus.

POTSNTIAL. RISKS

Because all ingredients we use in our study are food grade and FDA approved
for food applications, these samples pose no adverse health risk, provided the
subject has not been identified as being susceptible to an allergic reaction to the
previously listed sample ingredients. If you believe there is a potential of an
allergic reaction upon sniffing, notify the on-site sensory evaluation
coordinator and/or principle investigator immediately. You will be released from
participating in this study. Please note if you are injured as a result of your
participation in this research project, Michigan State University will assist you in
obtaining emergency care, if necessary, for you research related injuries. If you
have insurance for medical care, your insurance carrier will be billed in the
ordinary manner. As with any medical insurance, any costs that are not covered
or in excess of whatever are paid by your insurance, including deductibles, will
be your responsibility. Financial compensation for lost wages; disability, pain or
discomfort is not available. This does not mean that you are giving up any legal
rights you may have. You may contact Bruce Harte with any questions (355-
4555) or Patnarin Benyathiar (353-5143).

POTENTIAL BENEFITS

There are no benefits gained directly from your participation in this study.
However, your participation and response will provide us valuable data, which
can be used to identify optimum shelf life and packaging techniques for
asparagus.

147

ASSURANCE OF CONFIDENTIALTY

Any information obtained in connection with this study that could be identified
with you will be kept confidential by ensuring that all consent forms are securely
stored. All data collected and analyzed will be reported in an aggregate format
that will not permit associating subjects with specific responses or findings. Your
privacy will be protected to the maximum extent allowable by law.

WITHDRAWA_L FROM THIS STUDY
Participation in this study is voluntary. Your decision to refuse participation or

discontinue participation during this study will be honored promptly and
unconditionally.

148

 

APPENDIX C

QUESTIONNAIRE FOR SENSORY EVALUATION OF FRESH ASPARAGUS

SHELF LIFE STUDY

Name Date

 

1. Please evaluate the ODOR of the asparagus using the following scale. How
do you perceive the smell l odor in the sample?

5 = No smell, smells like fresh asparagus

4 = Slight asparagus smell

3 = Neither off odor or smells like asparagus (but not rotten smell)
2 = Off odor, slightly spoiled smell

1 = Very intense off odor smell, as rotten

2. Please evaluate the COLOR of the asparagus using the following scale. How
do you perceive the color in the sample? (Based on the color standard scale)

Stalk
5 = Extremely shiny and green as fresh green asparagus color
4 = Very green
3 = Moderately green (light green + light yellow)
2 = Very yellow
1 = Extremely yellow

Tips and Braces

5 = Very light purple (light purple + light green)
4 = Light purple (very little green)

3 = Moderately purple I moderately purple

2 = Dark purple / dark purple

1 = Very dark purple / very dark purple

149

 

. Please evaluate the TEXTURE of the asparagus using the following scale.
How do you perceive the texture (crispness or firm) in the sample?

5 = Very Firm I Crisp

4 = Firm / Crisp
3 = Moderately Soft /Firm
2 = Soft / Limp

1 = Very Soft/ Limp

. Please evaluate the OVERALL QUALITY of the asparagus using the following
scale. How do you perceive the overall appearance of asparagus?

5 = Very fresh / Best
Dark green and firm with tightly closed, compact tips, braces
tight to stalk, stalks are straight and glossy in appearance

4 = Some degradation of appearance
Tip not as compact, still green and healthy, possibly slight
curvature in tip

3 = Still Marketable
Head less green, some loss of rigidity in stalk, braces looser,
tip beginning to open, more curvature in stalk and tip

2 = Not marketable I Unacceptable
Some yellow appear and not stiff

1 = Rotten / Spoil

Completely limp, maybe mold, Very intense off odor smell,
rotten

150

 

APPENDIX D

CONSENT FORM FOR SENSORY EVALUATION OF COOKED ASPARAGUS

Department of School of Packaging and Food Science and Human Nutrition
Michigan State University

Consumer Consent Form
Dear Participant:

Several Michigan State University researchers are investigating consumer
acceptance of microwave cooking of fresh asparagus in alternative package
systems. We would like you to take about 15 minutes (including the time you
spent reading this letter) to help us evaluate 4 samples. We are asking for
volunteers, 18 or older, to look at, and taste samples and to answer a few
marketing questions. If you have a known food allergy to any of the following
possible FDA approved food ingredients, asparagus, please do not volunteer for
this study.

If you meet the above requirements, we would like you to look at, sniff and taste
the samples and answer questions related to the product quality. If you agree to
provide your evaluation based on the survey questionnaire, please sign the
consent form below. You will be given a coupon and/or food treats that are worth
less than $2 for your evaluation and completion of the survey.

If you believe there is a potential of an allergic reaction upon sniffing and
tasting, notify the on-site sensory evaluation coordinator and/or principle
investigator immediately. You will be released from participating in this study.
Please note if you are injured as a result of your participation in this research
project, Michigan State University will assist you in obtaining emergency care, if
necessary, for you research related injuries. If you have insurance for medical
care, your insurance carrier will be billed in the ordinary manner. As with any
medical insurance, any costs that are not covered or in excess of whatever are
paid by your insurance, including deductibles, will be your responsibility.
Financial compensation for lost wages; disability, pain or discomfort is not
available. This does not mean that you are giving up any legal rights you may
have. Your response is confidential and we will protect your confidentiality to the
full extent of the law. You are free to not answer any question you choose, but
please try to answer every question. We are not able to use incomplete
responses nor are we able to provide the incentive for incomplete responses.

151

 

If you have any questions about this consent form, during or after your
participation, please do not hesitate to contact the on-site sensory evaluation
leader and/or the principle investigator, Dr. Bruce Harte, Professor, School of
Packaging, via phone at 517-355-4555. He also can be reached by email at
harte@msu.edu for any inquiry you might have due to your participation in the
study.

PLEASE NOTE UPON YOUR SIGNING THIS CONSENT FORM, YOU
VOLUNTARILY AGREE TO PARTICIPATE IN OUR STUDY. YOUR
SIGNATURE INDICATES YOU HAVE READ THE INFORMATION PROVIDED
ABOVE AND THAT YOU HAVE HAD AN ADEQUATE OPPORTUNITY TO
DISCUSS THIS STUDY WITH THE PRINCIPLE INVESTIGATOR AND HAVE
HAD ALL YOUR QUESTIONS ANSWERED TO YOUR SATISFACTION. YOU
WILL BE GIVEN A COPY OF THIS CONSENT FORM WITH YOUR
SIGNATURE FOR YOUR RECORDS UPON YOUR REQUEST.

SIGNED . DATE

 

152

 

APPENDIX E

QUESTIONNAIRE FOR SENSORY EVALUATION OF COOKED ASPARAGUS

COOKING STUDY

You will be presented with 6 samples to evaluate. 3 samples will be served for
each set. When you are ready, lift the panel door and slide the READY portion of
the card under the door.

 

 

Do Not Eat the sample yet.

 

1. How do you like the Aroma of sample?
Like extremely

Like very much

Like moderately

Like slightly

Neither like nor dislike

Dislike slightly

Dislike moderately

Dislike very much

Dislike extremely

 

2. How do you like the Appearance and Color of sample?
Like extremely

Like very much

Like moderately

Like slightly

Neither like nor dislike

Dislike slightly

Dislike moderately

Dislike very much

Dislike extremely

 

Ew take a bite

153

 

3. How do you like the Flavor of sample?
Like extremely

Like very much

Like moderately

Like slightly

Neither like nor dislike

Dislike slightly

Dislike moderately

Dislike very much

Dislike extremely

 

4. How do you like the Texture of sample?
Like extremely

Like very much

Like moderately

Like slightly

Neither like nor dislike

Dislike slightly

Dislike moderately

Dislike very much

Dislike extremely

 

5. How do you like the Overall Acceptability of sample?
Like extremely

Like very much

Like moderately

Like slightly

Neither like nor dislike

Dislike slightly

Dislike moderately

Dislike very much

Dislike extremely

 

Comments I Suggestions:

 

 

6. Please rank the cooked asparagus in the order of your preference. Give your
most favorite cooked asparagus the ranking of 1.

(_) Sample 1 (actual blinding code will appear here during testing)

(__) Sample 2 (actual blinding code will appear here during testing)

(_) Sample 3 (actual blinding code will appear here during testing)

Rest ...Ranking Status: Incomplete

154

7. Please rank the asparagus products in the order of your preference. Give your
most preferred product the ranking of 1.

 

 

(_) Sample 1 (actual blinding code will appear here during testing)
(_) Sample 2 (actual blinding code will appear here during testing)
(_) Sample 3 (actual blinding code will appear here during testing)
Rest ...Ranking Status: Incomplete

Demographic Questionnaire

Do you typically eat asparagus?

Yes I:I No I:I
If Yes, how often?

Every day I:

2 to 3 time a week :1
Once a week :1

2 to 3 time a month :1
Once a month |:]

What types of asparagus products do you buy?
Fresh asparagus 1:]

Canned asparagus [:
Frozen asparagus 1:]
How you cook fresh asparagus?

Steam I:I
Microwave :1

Other, please explain

 

When choosing to buy the food product do you often choose based on

Package [:1
Price :3
Brand :

Other, please explain

 

155

Would you buy this product?
Yes 1:: N0 E::|

Gender
Female I::I Male :21

Age range

Less than 19 I::I
20-29 I:I
30-39 :3
4049 1:1
50 and over :I

Yearly household income

Less than $ 12,000 1::
$ 12,000 - $ 19,000 [:3
$ 20,000 - $ 29,000 I:
$ 30,000 - $ 39,000 I::I
$ 40,000 - $ 49,000 [:1
$ 50,000 - $ 59,000 I::I

$ 60,000 and over :
Marital Status

Single E:I
Married :1
Divorced :1
Widowed [:2

156