HYPERBARIC TREATMENT TO ENHANCE QUALITY ATTRIBUTES OF FRESH HORTICULTURAL PRODUCE

By

Bernard Goyette

Department of Bioresource Engineering

McGill University, Montreal

Quebec, Canada

February, 2010

A thesis submitted to McGill University in partial fulfillment of the requirements of the

degree of Doctor of Philosophy

Bernard Goyette 2010

I

ABSTRACT

Bernard Goyette Ph.D. (Bioresource Engineering)

HYPERBARIC TREATMENT TO ENHANCE QUALITY ATTRIBUTES OF FRESH HORTICULTURAL PRODUCE

An experimental hyperbaric system was conceptualized, designed and built to

explore the effect of hyperbaric treatment on the respiration rate (RR), respiratory

quotient (RQ) and quality attributes of tomato. Housing five containers that could

be individually pressurized from 1 to 9 atmabs, the respirometer was equipped

with a flow meter, control valve, pressure transducer; CO2 and O2 gas analyzer

and type T thermocouples, all connected to a data acquisition and control card. A

software interface was programmed to allow control of the air flow rate through

the proportional valve of the flow meter, based on a PID (Proportional, Integral,

and Derivative) algorithm.

Hyperbaric treatments on tomato fruit showed RR to be inversely proportional to

the pressure applied: RR was reduced by 20% at 9 atmabs compared to the

control (1 atmabs). At the onset of pressure application the RQ was low and

increased to reach a value of approximately 1 within 120 hours. Low RQ values

were caused by solubilization of CO2 in the tomato cells at the beginning of the

process.

Early breaker stage tomatoes were subjected to hyperbaric pressures of 1, 3, 5, 7

or 9 atmabs for different durations (5, 10 or 15 days) at 13C, followed by a

storage period of 12 days at 20oC. The effect of hyperbaric treatment on

postharvest quality of tomato fruits was evaluated with an emphasis on weight

loss, firmness, color, lycopene content, titratable acidity (TA) and total soluble

solids (TSS). Based on firmness values, control tomatoes were no longer

II

acceptable for consumption after 12 days of post-treatment storage. Being

subjected to hyperbaric pressures of 7 and 9 atmabs for 15 days caused

irreversible physiological damage to the tomatoes.

Treatments of 3, 5 or 7 atmabs applied over 10 days, or 5 atmabs applied over 5

days maintained marketable firmness. The lowest weight loss occurred with

treatments of 3 or 5 atmabs for 5 days, or 5 atmabs for 10 days.

Lycopene content of the tomatoes was improved by hyperbaric pressure followed

by 12 days of maturation. The greatest lycopene content 28% more than in the

control was obtained for tomatoes subjected to 5 atmabs over 10 or 15 days.

III

RSUM

Bernard Goyette Ph.D (Gnie des bioressources)

TRAITEMENT HYPERBARE POUR AMLIORER LA QUALIT DES PRODUITS HORTICOLES FRAIS

Un respiromtre hyperbare exprimental a t conu et construit pour tudier

l'effet du traitement hyperbare sur le taux de respiration (RR), le quotient

respiratoire (RQ) et les attributs de qualit de la tomate. Il tait compos de cinq

contenants qui pouvaient tre individuellement pressuriss de 1 9 atmabs. Le

respiromtre tait quip d'un dbitmtre, valve, capteur de pression, un

analyseur de CO2 et O2 et de thermocouples de type T. Tous les capteurs taient

relis une carte dacquisition de donnes et de contrle. Un logiciel servant

dinterface a t programm pour permettre le contrle du dbit d'air travers la

valve proportionnelle du dbitmtre bas sur un contrleur PID (proportionnel,

intgral, drive). Les traitements hyperbares ont t effectus sur les tomates et

il a t observ que RR tait inversement proportionnel la pression. Le RR a

t rduit de 20% 9 atmabs compar au contrle (1 atmabs). Au dbut de

l'application de pression le RQ tait faible et a augment graduellement durant

120 heures pour atteindre une valeur d'environ 1. Les faibles valeurs de RQ ont

t vraisemblablement causes par la solubilisation CO2 dans la chair des

tomates au dbut du processus. Leffet de la pression hyperbare a t test sur

la qualit de la tomate. Les pressions utilises taient de 1, 3, 5, 7 ou 9 atmabs et

ont t utilises avec trois diffrentes dures de traitement: 5, 10 ou 15 jours,

13C, et suivie d'une priode dentreposage de 12 jours 20C. L'effet du

traitement hyperbare sur la qualit postrcolte de la tomate a t tudi en

mettant l'accent sur la perte de poids, la fermet, la couleur, le lycopne, l'acidit

titrable (TA), et les solides solubles totaux (TSS). Aprs 12 jours dentreposage,

IV

la fermet de toutes les tomates du groupe contrle (1 atmabs) tait un niveau

non acceptable pour la consommation. Le maintient pendant 15 jours de

pressions hyperbares leves (7 et 9 atmabs) ont caus des dgts

physiologiques irrversibles chez les tomates. Les valeurs de fermet

considres commercialisables ont t obtenues par des traitements de 3, 5 ou

7 atmabs maintenus pendant 10 jours ou 5 atmabs maintenus pendant 5 jours. Les

plus faibles valeurs de perte de poids ont t observes avec des traitements de

3 ou 5 atmabs pendant 5 jours ou 5 atmabs pendant 10 jours. La teneur en

lycopne des tomates sest amliore avec des pressions hyperbares suivis de

12 jours de maturation. La plus haute valeur de lycopne a t obtenue avec des

tomates soumises 5 atmabs pendant 10 ou 15 jours. Le taux de lycopne tait

significativement plus lev pour ces tomates soit 28% plus lev que celles du

groupe contrle.

V

ACKNOWLEDGMENTS

I would like to express my sincere gratitude to my academic supervisor, Professor

Vijaya Raghavan, for his support throughout this study.

My sincere thanks to my co-supervisor, Dr. Clment Vigneault, for his support

and mentorship. Thank you for being patient with me and giving me the time to

produce a quality work. Overall, thank you for giving me the opportunity to

experience graduate studies.

I sincerely thank Dr. Marie Thrse Charles, for her help in the study of the

physiological aspects.

I express my special thanks to Jrme Boutin and Dominique Roussel, my

colleagues at Agriculture and Agri-food Canada, and to my daughter Amlie

Goyette, for their great help.

Thanks to my children, Amlie, Mathieu-Vincent, Nicolas and Thomas, who

understood I needed to work so often.

A special thanks to my friend Simona Nemes: you were my rayon de soleil on the

campus.

Finally, I would like to thank my wife, Marlne Pich, for her assistance and

collaboration during these interminable working hours. I sincerely believe that this

accomplishment would not have been possible without your support.

I gratefully acknowledge the financial support of Agriculture and Agri-Food

Canada.

VI

TABLE OF CONTENTS

ABSTRACT............................................................................................................ I

RSUM.............................................................................................................. III

ACKNOWLEDGMENTS....................................................................................... V

TABLE OF CONTENTS...................................................................................... VI

LIST OF FIGURES.............................................................................................. XI

LIST OF TABLES ............................................................................................. XVI

NOMENCLATURE .......................................................................................... XVII

1. GENERAL INTRODUCTION ........................................................................1 1.1. POSTHARVEST HISTORY CONSIDERING CONSUMER DEMAND IN

NORTH AMERICA ............................................................................................1 1.2. FUNCTIONAL FOOD AND NUTRACEUTICAL INDUSTRY.........................4 1.3. TOMATO.......................................................................................................5

1.3.1. LYCOPENE.........................................................................................6 1.3.2. TOMATO AND HUMAN HEALTH .......................................................6 1.3.3. TOMATO PRODUCTION ....................................................................9

1.4. PROBLEM STATEMENT..............................................................................9 2. OBJECTIVES..............................................................................................11 2.1. HYPOTHESIS.............................................................................................11 2.2. MAIN OBJECTIVES....................................................................................11 3. LITERATURE REVIEW...............................................................................12 3.1. INTRODUCTION ........................................................................................12 3.2. RESPIRATION RATE .................................................................................13

3.2.1. RESPIRATION DEFINITION.............................................................13 3.2.1.1. RESPIRATION DEFINITION....................................................................14 3.2.1.2. MONITORING METABOLIC ACTIVITY ...................................................15

3.2.2. RESPIRATION QUOTIENT DEFINITION..........................................15 3.2.3. RELATIONSHIP BETWEEN RESPIRATION RATE AND

RESPIRATION QUOTIENT AND THEIR EFFECT ON PRODUCT METABOLISM ...................................................................................16

3.2.4. ENVIRONMENTAL FACTORS AFFECTING RESPIRATION RATE AND RESPIRATION QUOTIENT ......................................................16

VII

3.2.5. RQ VALUES AND THEIR SIGNIFICANCE .......................................18 3.2.6. METHODS TO MEASURE RESPIRATION RATE AND RQ .............19

3.3. PHYSICAL TREATMENT ...........................................................................20 3.3.1. HEAT.................................................................................................20

3.3.1.1. THERMOTOLERANCE............................................................................20 3.3.1.2. EFFECTS ON DISINFECTION AGAINST HUMAN PATHOGENS ..........21

3.3.1.2.1. CANTALOUPE AND MELONS .........................................................21 3.3.1.2.2. LEAFY VEGETABLES ......................................................................21 3.3.1.2.3. TOMATOES......................................................................................22

3.3.2. UV-C..................................................................................................22 3.3.2.1. EFFECTS ON DISEASE ..........................................................................23 3.3.2.2. HORMESIS EFFECTS IMPROVEMENTS OF QUALITY

ATTRIBUTES...........................................................................................23 3.3.2.2.1. POSITIVE CHANGES.......................................................................23 3.3.2.2.2. ADVERSE EFFECTS........................................................................24

3.3.2.3. EFFICACY OF UV TREATMENT.............................................................24 3.3.3. PRESSURE.......................................................................................25

3.3.3.1. HIGH PRESSURE PROCESSING (HPP) ................................................27 3.3.3.1.1. EFFECTS ON PATHOGEN ..............................................................27 3.3.3.1.2. EFFECTS ON ENZYMES .................................................................28 3.3.3.1.3. EFFECTS ON PHYSICAL PROPERTIES AND QUALITY OF

PROCESSED FRUITS AND VEGETABLES ........................................29 3.3.3.2. HPP COMBINED WITH MILD THERMAL TREATMENT .........................29 3.3.3.3. HPP COMBINED WITH LOW-TEMPERATURE TREATMENT ...............30

3.3.3.3.1. EFFECTS ON RESPIRATION RATE OF FRUITS AND VEGETABLES UPON STORAGE ........................................................31

3.3.3.4. HYPOBARIC AND HYPERBARIC PRESSURE TREATMENT................31 3.3.3.4.1. HYPOBARIC PRESSURE TREATMENT..........................................31 3.3.3.4.2. EFFECTS ON PATHOGENS AND DISEASES.................................32 3.3.3.4.3. EFFECTS ON FRUITS AND VEGETABLES CONSERVATION.......33 3.3.3.4.4. HYPERBARIC PRESSURE TREATMENT .......................................34 3.3.3.4.5. EFFECTS ON FRUITS AND VEGETABLES QUALITY ....................34

3.3.3.5. BENEFICIAL SUBSTANCES AND FUNCTIONAL PROPERTIES OF FRUITS AND VEGETABLES INDUCED BY PRESSURE TREATMENT.35

VIII

3.4. TOMATO.....................................................................................................36 3.4.1. PHYSIOLOGY OF TOMATO.............................................................36

3.4.1.1. COMPOSITION........................................................................................36 3.4.1.2. CHARACTERISTICS ...............................................................................36

3.4.2. QUALITY PARAMETERS..................................................................37 3.4.2.1. MATURITY...............................................................................................38 3.4.2.2. COLOR ....................................................................................................38

3.4.2.2.1. COLOR MEASUREMENT.................................................................40 3.4.2.3. TEXTURAL QUALITY ..............................................................................40 3.4.2.4. TOMATO SOLIDS....................................................................................40 3.4.2.5. FLAVOUR QUALITY ................................................................................41

3.5. LYCOPENE ................................................................................................41 3.5.1. LYCOPENE IN TOMATO ..................................................................41 3.5.2. LYCOPENE AND HUMAN HEALTH .................................................42

3.6. SUMMARY..................................................................................................43 4. CONCEPTUALIZATION, DESIGN AND EVALUATION OF A

HYPERBARIC RESPIROMETER ...............................................................45 4.1. INTRODUCTION ........................................................................................45 4.2. PRELIMINARY WORKBENCH ...................................................................48

4.2.1. RESPIROMETER DESIGN ...............................................................48 4.2.2. CALIBRATION OF THE RESPIROMETER.......................................53 4.2.3. EVALUATION OF THE EFFICACY OF THE SYSTEM TO

MEASURE THE RESPIRATION RATE OF LIVING PRODUCE .......53 4.3. RESULTS AND DISCUSSION....................................................................55

4.3.1. RESPIROMETER DESIGN ...............................................................55 4.3.2. CALIBRATION OF THE RESPIROMETER.......................................60 4.3.3. EVALUATION OF THE EFFICACY OF THE SYSTEM TO

MEASURE THE RESPIRATION RATE OF LIVING PRODUCE .......62 4.4. CONCLUSION............................................................................................65 4.5. REFERENCES ...........................................................................................65 CONNECTING TEXT..........................................................................................67 5. EFFECT OF HYPERBARIC TREATMENT ON RESPIRATION RATE

AND RESPIRATORY QUOTIENT OF TOMATO ........................................68 5.1. INTRODUCTION ........................................................................................68

IX

5.2. MATERIAL AND METHOD.........................................................................70 5.2.1. HYPERBARIC RESPIROMETER DESIGN.......................................70 5.2.2. BIOLOGICAL MATERIAL ..................................................................73

5.3. EXPERIMENTAL DESIGN..........................................................................73 5.4. RESULTS AND DISCUSSION....................................................................74

5.4.1. RESPIRATION RATE CALCULATION..............................................75 5.4.2. MODEL FOR PREDICTING THE RESPIRATION RATE ..................81 5.4.3. RQ VALUES AND THEIR SIGNIFICANCE .......................................89 5.4.4. EFFECT OF HYPERBARIC TREATMENT ON RR AND RQ ............95

5.5. CONCLUSION............................................................................................96 5.6. REFERENCES ...........................................................................................97 CONNECTING TEXT..........................................................................................99 6. EFFECT OF HYPERBARIC TREATMENT ON QUALITY ATTRIBUTES

OF TOMATO.............................................................................................100 6.1. INTRODUCTION ......................................................................................100 6.2. MATERIALS AND METHODS ..................................................................103

6.2.1. HYPERBARIC SYSTEM..................................................................103 6.2.2. BIOLOGICAL MATERIAL ................................................................106 6.2.3. EXPERIMENTAL SET UP...............................................................106

6.2.3.1. DECOMPRESSION ...............................................................................107 6.2.4. EVALUATION OF QUALITY PARAMETERS..................................108

6.2.4.1. WEIGHT LOSS ......................................................................................108 6.2.4.2. FIRMNESS.............................................................................................108 6.2.4.3. COLOR AND LYCOPENE .....................................................................109 6.2.4.4. TOTAL SOLUBLE SOLIDS (TSS) AND TITRATABLE ACIDITY (TA)....111

6.2.5. STATISTICAL ANALYSIS ...............................................................112 6.3. RESULTS AND DISCUSSION..................................................................112

6.3.1. WEIGHT LOSS................................................................................113 6.3.1.1. OPENING...............................................................................................113 6.3.1.2. AFTER 12 DAYS OF STORAGE ...........................................................115

6.3.2. FIRMNESS......................................................................................115 6.3.2.1. OPENING...............................................................................................117 6.3.2.2. AFTER 12 DAYS OF STORAGE ...........................................................117

X

6.3.3. COLOR AND LYCOPENE...............................................................120 6.3.4. COLOR............................................................................................120

6.3.4.1. OPENING...............................................................................................120 6.3.4.2. AFTER 12 DAYS OF STORAGE ...........................................................122

6.3.5. LYCOPENE.....................................................................................122 6.3.5.1. OPENING...............................................................................................122 6.3.5.2. AFTER 12 DAYS OF STORAGE ...........................................................126

6.3.6. TITRATABLE ACIDITY....................................................................127 6.3.6.1. OPENING...............................................................................................127 6.3.6.2. AFTER 12 DAYS OF STORAGE ...........................................................129

6.3.7. TOTAL SOLUBLE SOLIDS (TSS) ...................................................129 6.3.7.1. OPENING...............................................................................................129 6.3.7.2. AFTER 12 DAYS OF STORAGE ...........................................................129

6.3.8. TSS TA RATIO .............................................................................133 6.4. GENERAL DISCUSSION..........................................................................133 6.5. CONCLUSION..........................................................................................136 6.6. REFERENCES .........................................................................................137 7. GENERAL SUMMARY AND CONCLUSIONS..........................................141 8. RECOMMENDATIONS FOR FUTURE STUDIES ....................................144 9. CONTRIBUTIONS TO KNOWLEDGE ......................................................145 10. REFERENCES .........................................................................................146

XI

LIST OF FIGURES

Figure 3.1: Representation of pressure range treatment and the type of

produce on which the treatment can be applied.

26

Figure 3.2: Maturity and ripening stages of tomatoes. 39

Figure 4.1: Pictorial and schematic view of the hyperbaric respirometer.

Dotted lines represent the gas flow pathway thru the

dynamic respiration system.

49

Figure 4.2: Chamber and equipment details of the dynamic respiration

system developed.

50

Figure 4.3: Theoretical % of flushing during the calibration as a function

of time using the general dilution equation (Eq. 4.1). The

volume used was 442 mL and an airflow rate of 50 mL min-1.

54

Figure 4.4: Respiration rate pattern of 200 g tomato stored inside of the

442 mL airtight chamber pressurized at 2 atmabs and

maintained at 13C with an airflowrate of 50 mL min-1.

56

Figure 4.5: Respiration rate pattern using the outer chamber having a

volume of 8863 mL with 1218 g of tomato at 13C and

pressurized at 7 atmabs and an airflow rate of 110 mL min-1.

57

Figure 4.6: Error of the respiration rate (RR) reading as a function of the

RR.

58

Figure 4.7: Air flow rate (mL min-1) required to maintain the CO2concentration of the exhausting gas at 1478 ppm as a

function of the commodity respiration rate (mL of CO2 min-1).

59

XII

Figure 4.8: Calibration curves obtained using the dynamic respiration

system developed and a calibration gas containing

1478 ppm of CO2.

61

Figure 5.1: Schema of the automated respirometer developed to

measure the respiration rate and the respiration coefficient

using a continuous flow through system.

71

Figure 5.2: Detail of the closed container unit showing the air inlet for

injecting Qin, the air outlet through which the airflow Qoutexhausts from the system, and the inside volume (V) and

the gas (G) produced or used by the produce.

72

Figure 5.3: Respiration rate (RRCO2) of tomato based on CO2 production

as a function of time for various hyperbaric pressure and

equivalent CO2 partial pressure.

76

Figure 5.4: Respiration rate (RRO2) of tomato based on O2 production as

a function of time for various hyperbaric pressure and

equivalent CO2 partial pressure.

77

Figure 5.5: Respiration quotient (RQ) of tomato as a function of time for

various hyperbaric pressure and equivalent CO2 partial

pressure.

78

Figure 5.6: Linear portion of respiration rate data based on CO2 used for

linear regression analysis.

79

Figure 5.7: Linear portion of respiration rate data based on O2 used for

linear regression analysis.

80

Figure 5.8: Respiration rate based on CO2 released as a function of

CO2 partial pressures. The respiration rate presented in this

figure is obtained from the intercept of the linear regression

analysis presented in Table 1.

83

XIII

Figure 5.9: Decrease of respiration rate in time based on CO2 released

as a function of CO2 partial pressures. The respiration rate

presented in this figure is obtained from the slope of the

linear regression analysis presented in Table 1.

84

Figure 5.10: Respiration rate based on O2 released as a function of CO2partial pressures. The respiration rate presented in this

figure is obtained from the intercept of the linear regression

analysis presented in Table 2.

86

Figure 5.11: Decrease of respiration rate in time based on O2 released as

a function of CO2 partial pressures. The respiration rate

presented in this figure is obtained from the slope of the

linear regression analysis presented in Table 2.

87

Figure 5.12: Comparison between the theoretical RR calculated using

Eq. 5.17 (continuous lines) and experimental RR data

measured (data points).

90

Figure 5.13: Apparent RQ results calculated for the first 120 hours after

submitting tomato fruits to different absolute pressures

ranging from 1 to 9 atmabs.

92

Figure 5.14: Respiration coefficient (RQ) measured after CO2 gas

reached equilibrium during pressure tomato fruit treatments

at different absolute pressures ranging from 1 to 9 atmabs.

94

Figure 6.1: Hyperbaric system used to test the effect of pressure on

tomato.

104

Figure 6.2: The percentage of tomato weight loss after 5, 10 and 15

days of continuous hyperbaric treatment at a temperature of

13C and 95% RH. Vertical bars indicate standard deviation.

114

XIV

Figure 6.3: The percentage of tomato weight loss after 12 days

maturation at 20C and 80% RH for 5, 10 and 15 days of

continuous hyperbaric treatment at a temperature of 13C

and 95% RH. Vertical bars indicate standard deviation.

116

Figure 6.4: Initial tomato firmness and after 5, 10 and 15 days of

continuous hyperbaric treatment at a temperature of 13C

and 95% RH. The firmness is expressed in N mm-1 required

to penetrate the tomato by 3 mm using a flat punch 6 mm

diameter. Vertical bars indicate standard deviation.

118

Figure 6.5: Tomato firmness after 12 days maturation at 20C and 80%

RH for 5, 10 and 15 days of continuous hyperbaric treatment

at a temperature of 13C and 95% RH. The firmness is

expressed in N mm-1 required to penetrate the tomato by

3 mm using a flat punch 6 mm diameter. Vertical bars

indicate standard deviation. Vertical bars indicate standard

deviation.

119

Figure 6.6: Initial Tomato color and after 5, 10 and 15 days of

continuous hyperbaric treatment at a temperature of 13C

and 95% RH. Vertical bars indicate standard deviation.

121

Figure 6.7: Tomato color after 12 days maturation at 20C and 80% RH

for 5, 10 and 15 days of continuous hyperbaric treatment at

a temperature of 13C and 95% RH. Vertical bars indicate

standard deviation.

123

Figure 6.8: Lycopene concentration of tomato after 5, 10 and 15 days of

continuous hyperbaric treatment at a temperature of 13C

and 95% RH. Vertical bars indicate standard deviation.

124

XV

Figure 6.9: Lycopene concentration of tomato after 12 days maturation

at 20C and 80% RH for 5, 10 and 15 days of continuous

hyperbaric treatment at a temperature of 13C and 95% RH.

Vertical bars indicate standard deviation.

125

Figure 6.10: Initial TA of tomato and after 5, 10 and 15 days of

continuous hyperbaric treatment at a temperature of 13C

and 95% RH. Vertical bars indicate standard deviation.

128

Figure 6.11: TA of tomato after 12 days maturation at 20C and 80% RH

for 5, 10 and 15 days of continuous hyperbaric treatment at

a temperature of 13C and 95% RH. Vertical bars indicate

standard deviation.

130

Figure 6.12: Initial TSS of tomato and after 5, 10 and 15 days of

continuous hyperbaric treatment at a temperature of 13C

and 95% RH. Vertical bars indicate standard deviation.

131

Figure 6.13: TSS of tomato after 12 days maturation at 20C and 80%

RH for 5, 10 and 15 days of continuous hyperbaric treatment

at a temperature of 13C and 95% RH. Vertical bars indicate

standard deviation.

132

Figure 6.14: Initial TSS/TA ratio of tomato and after 5, 10 and 15 days of

continuous hyperbaric treatment at a temperature of 13C

and 95% RH. Vertical bars indicate standard deviation.

134

Figure 6.15: Initial TSS/TA ratio of tomato after 12 days maturation at

20C and 80% RH for 5, 10 and 15 days of continuous

hyperbaric treatment at a temperature of 13C and 95% RH.

Vertical bars indicate standard deviation.

135

XVI

LIST OF TABLES

Table 1.1 : Ripening index values for tomato fruits at different color

stages. Adapted from Lopez Camelo and Gomez, 2004.

8

Table 4.1 : Respiration rate (RR) of tomato fruits exposed to a pressure

of 2 and 7 atmabs and a temperature of 13C.

64

Table 5.1 : Parameter of the linear regression analysis of respiration

rate based on CO2 production as a function of time for

various CO2 partial pressures (Fig 5.6).

82

Table 5.2 : Parameter of the linear regression analysis of respiration

rate based on O2 production as a function of time for various

CO2 partial pressures (Fig 5.7).

85

Table 5.3 : Parameter of the linear regression analysis of RQ as a

function of time for various CO2 partial pressures (Fig. 13).

93

Table 6.1 : Ripening index values for tomato fruits at different color

stages. Adapted from Lopez Camelo and Gomez, 2004.

110

XVII

NOMENCLATURE

= confidence interval used during statistical analysis

a* = CIE standard nomination for one of the three colour components

obtained from a chromameter

b* = CIE standard nomination for one of the three colour components

CO2 = difference in CO2 concentration between the inlet and outlet of the

respiration chamber, ppm

C = concentration of a gas inside the respiration chamber, ppm

C1 = constant

Cfinal = final concentration of diluted gas, ppm

CIE = Commission Internationale de lclairage

Cinitial = initial concentration of the gas to be diluted, ppm

Dt = dilution time, min

H = color parameter hue angle

L* = CIE standard nomination for one of the three colour components

obtained from a chromameter

m = mass of produce, kg

N = number of samples required to produce a significant difference

O2 = difference in O2 concentration between the inlet and outlet of the

respiration chamber, ppm

p = pressure inside of the respiration chamber, atmabs

Q = flow rate, mL h-1 or mL min-1

RQ = ratio between the amounts of CO2 released (Rx) over the amount

of O2 consumed (Ry)

XVIII

RR = respiration rate, mL gas kg-1 h-1

RRCO2 = respiration rate, mL CO2 kg-1 h-1

RRD = respiration rate decrease in time, mL gas kg-1 h-1

RRmeasured = measured respiration rate, mL gas kg-1 h-1

RRO2 = respiration rate, mL O2 kg-1 h-1

RRreal = real respiration rate, mL gas kg-1 h-1

Rx = amounts of CO2 released, mL CO2 kg-1 h-1

Ry = amounts of O2 released, mL O2 kg-1 h-1

2xS ,

2yS = standard deviation of the population x and y, respectively,

t = time, h

t1 = time at the event 1, h

t2 = time at the event 2, h

t2 = two-tailed Student t-test value

t = time differential, h

V = void volume of gas to be diluted in the chamber, mL or L

v = CO2 volume difference inside the respiration chamber, mL or L

x , y = mean values of the population x and y, respectively

CHAPTER I

1. GENERAL INTRODUCTION

1.1. POSTHARVEST HISTORY CONSIDERING CONSUMER DEMAND IN

NORTH AMERICA

Quality attributes of fruits and vegetables after harvest have been a worldwide

concern for many years. Over the XXth century, innovations of all kinds have

taken place to keep produce fit for consumption year round, ranging from natural

cold, cooking and canning, salting and drying to refrigeration and transformation

with the advent of new technologies such as fuel power, electricity and

biotechnology.

A 1921 article in the New York Times reported the studies of Dr. H.B Cox, who

suggested that eating fresh fruits and vegetables was important to prevent

malnutrition (Cox, 1921). The difficulty reported at that time was the unavailability

of such commodities, as fresh vegetables delivered to households were often no

longer fresh due to poor conservation methods. Given the necessity of making

available fresh fruits and vegetables that would stay fresh for a certain time on

the market counter without damage caused by diseases, transport or handling,

conservation techniques were the subject of many studies.

In 1950, the cooling of fruits and vegetables had increased the availability of a

wide variety of produce, and to the establishment of systems for storage and long

distance transportation. These changes brought new challenges to the field. It

became obvious that not all commodities required the same cooling temperature

to preserve food quality, and that improper conservation temperatures could

enhance physiological damage. Several hours were needed to lower the produce

temperature and since the temperature in the product was non-uniform, it allowed

decay-organisms to grow (Bratley and Wiant, 1950).

2

Considering the non-uniformity problem of the cooling systems, the principle of

pre-cooling emerged. Pre-cooling with ice and forced cold-air was investigated

by Bratley and Wiant in 1950. Hydrocooling was introduced in the late 50s, but

represented an important source of inoculums for pathogens as water was

constantly re-circulated through the mass of produce. Contamination was

reduced by the addition of chemicals to the cooling water (Smith, 1962).

Diseases affecting fruits and vegetables after harvest were long known to be

detrimental to conservation. Different antiseptic treatments were proposed over

the years (Fulton and Bowman, 1925; Pryor and Baker, 1950), but it is only in the

50s that diseases affecting fresh fruits and vegetables became a main concern

not only for producers but for handlers and consumers. Some diseases appeared

to arise in the field but others resulted from poor operating conditions after

harvest. Increasing attention was then given to treatments for decay prevention

carried out after harvest and prior to shipment (Bratley and Wiant, 1950). Many

methods were investigated to reduce postharvest decay, most of them of a

chemical nature. Chemicals were applied through dipping or washing of the fresh

produce, by fumigation of the storage facility or by coating the wrappers or liners

of the shipping boxes. The chemicals used, fungicides, bactericides and

antibiotics, were toxic to microorganisms (Smith, 1962). Since a cold chain was

not in practice in the earlier years, it led to many designs of conservation devices

over the last century. In 1917, a Patent was given for a sealed container

subjected to the cooling effect caused by the expansion of a compressed gas. It

was proposed to maintain organic material freshness (Darden, 1917). In 1918,

the idea of vacuum followed by an addition of carbon dioxide to a sealed

container to reduce the tendency to decay or ferment was proposed. The

recommendation was to apply CO2 at 4 atm to maintain freshness from a few

hours to a few weeks (Franks, 1918). In 1931, Edward Milani made a request to

the US Patent office to protect the invention of the reduced oxygen and high

carbon dioxide sealed container to maintain produce quality (Milani, 1931). He

explained the principle of controlled atmosphere storage, how produce reacted

and the importance of venting the container to maintain product quality. In the

3

1940s, some studies explored the use of low O2 or high CO2 atmosphere for the

reduction of respiration rate and conservation at a larger scale. British studies

found that the storage life of apples could be doubled by holding them at 14%

CO2 and 8% O2 (Bratley and Wiant, 1950). These results led to the

implementation of a number of such systems in England. As CA storage became

widely used, it was observed that in certain cases it altered the quality of the

produce. CA storage expanded worldwide and was widely evaluated and

optimized to maintain an optimal quality of fresh produce (Murata and Minamide,

1970; Little et al., 1973; Gariepy et al., 1984; Reust et al., 1984; Goyette et al.,

2002; Amodio et al., 2005; Lvesque et al., 2006).

After the Second World War, mass marketing strategies for food production

became the norm, resulting in the export of products worldwide. There were

fewer varieties available (Cook, 2002). Efforts were made to export large

quantities of non-perishable products, as well as canned or easily preserved

commodities at relatively lower temperatures (12C). The canning industry was

very important at that time (Bratley and Wiant, 1950). With the demographic and

lifestyle trends of the 1970s, changes occurred and consumers demands

diversified. Targeted marketing replaced mass marketing in the 80s and kept

changing from there on (Cook, 2002). Between 1978 and 1988, fresh vegetable

consumption per capita increased by 26%. In the 90s, 98% of American

consumers stated that the quality of fresh fruits and vegetables had a determinant

influence on where they shopped for food (Food Marketing Institute, 1990).

A new trend towards organic foods also influenced the late 90s. Knowing the

public health and environmental risks related to the use of pesticides, especially

post-harvest fungicide treatments, favored the introduction of integrated pest

management programs (IPM) and environmentally friendly technologies to

improve the quality of fruits and vegetables from the field to the consumers table.

4

1.2. FUNCTIONAL FOOD AND NUTRACEUTICAL INDUSTRY

Fruits and vegetables are a good source of vitamins, minerals and

phytochemicals. Phytochemicals are non-nutritive bioactive plant substances

considered to have beneficial effects on human health (Basu et al., 2007). People

are more and more informed and aware of the importance of these

phytochemicals, often presented to consumers as antioxidants. Antioxidants are

protective agents that significantly delay or prevent oxidative damage in cells

caused by reactive oxygen species and appeared to have a wide range of

anticancer and antiatherogenic properties (Agarwal and Rao, 2000). The

presence of natural plant compounds have been found to be further enhanced by

inducing known quantities of physical stress. Heat treatment, controlled

atmosphere storage, UV radiation and other chemical-free treatments have been

studied. Many researches have reported that such stress or treatments induce

positive physiological changes to the fruits and vegetables, such as natural

disease resistance or improved quality attributes (Hodges and DeLong, 2007).

The concept is called plant hormesis and is, by definition, the stimulation of a

beneficial plant response by low or sub-lethal dosage of an elicitor such as a

chemical, biological or physical stress (Luckey, 2003). The natural disease

resistance of harvested horticultural crops induced by elicitors has been

investigated (Terry and Joyce, 2004) and is very attractive considering the

importance of the concept of reducing the use of pesticides and the enhancement

of quality of fresh produce to serve as a functional food.

Functional foods are products that are similar in appearance to conventional food,

are consumed as part of a usual diet, and have demonstrated health benefits

beyond basic nutrition such as the prevention, protection and treatment of chronic

diseases (Anon., 2005; Basu et al., 2007). A nutraceutical is a product isolated or

purified from foods, demonstrated to have physiological benefit or provide

prevention, protection and treatment against diseases (Basu et al., 2007). In

5

recent years, functional food and nutraceutical industry have been constantly

growing in the global marketplace.

Agriculture and Agri-Food Canada has presented the Canadian Food Trends to

2020 - A long range consumer outlook report (Anon., 2005). The rapidly growing

market for functional food and natural health products is benefiting Canadas

functional foods and nutraceuticals (FFN) industry. According to Statistics

Canada (Anon., 2008), in 2004 this industry generated $2.9 billions in total

revenues, representing a 15% increase since 2002. But Canada has a long way

to go to compete with other countries. In 2004, Canadas production represented

only 3% of the global market. The United States of America is the World leader

with 35% of the market, followed by Japan and the European Union. Other

Eastern Countries such as China and India produce large quantities of traditional

functional food products, but are limited in access to World markets by the

necessity to properly label and assess the health effects of the products for

export. As of 2006, Australia and New Zealand are emerging as international

competitors. South, Central and Latin America are still developing and the

principle of functional food lacks popularity. African markets are still not well

organized although functional food and nutraceuticals are part of the African

culture. In 2007, the functional foods and nutraceutical industry represented

$75.5 billion US and is expected to grow to $167 billion by 2010 (Basu et al.,

2007).

1.3. TOMATO

Tomato is the third most important fresh vegetable consumed in Canada (Anon.,

2008), the second most important vegetable crop in the world next to potato, and

is the leading processed vegetable available (Gould, 1992). The origin of tomato

is somewhat uncertain but it appears that it started out as a wild growing fruit in

South America. The name tomato is derived from the Aztec word xitomate but

the wild tribes of Mexico called it tomati. The fruit was taken to Europe from

Mexico or Peru during the early 16th century and was grown extensively in Italy,

6

where it was called pomi doro or golden apple. As of 1800, six varieties of

tomatoes were grown for market purposes in Europe. Its large production brought

curiosity and interest in England and North America. Tomato was first brought to

America in 1798 but the fruit was not sold on the market until 1829. It then rapidly

gained popularity thus making it almost indispensable today, as it is used fresh,

canned or processed as soup, sauce, or ketchups (Gould, 1992). Globally, the

tonnage of tomato production and per capita consumption has kept increasing. In

the U.S., per capita consumption of tomato has increased by almost 20%

between 1985 and 2000 (FAOSTAT Database, 2004). Tomato consumption is

anticipated to keep increasing since tomato fruits have been well identified as an

important source of lycopene, a most potent antioxidant, and associated with high

vitamine C and A content, which have considerable health benefits.

1.3.1. LYCOPENE

Lycopene is a carotenoid, an acyclic isomer of -carotene. It is the most

predominant carotenoid in human plasma and is found to concentrate in the

adrenal gland, testes, liver and prostate gland. It is a natural pigment synthesized

by plants and microorganisms but not by animals. As other antioxidants, like

vitamin E, vitamin C and polyphenols, carotenoids are available from plant food.

The lycopene present in natural plant sources is the most thermodynamically

stable form (Agarwal and Rao, 2000).

Antioxidant properties increase cellular defence against oxidative damage but

lycopene may also have bioactivities capable of enhancing DNA repair (Astley

and Elliott, 2005).

1.3.2. TOMATO AND HUMAN HEALTH

Some genetic transformation, like genetically modified organisms (GMO), to

improve the quality or resistance of eatable products is not well accepted by

consumers. Hence alternative and natural sources should be favoured.

7

Tomatoes contain naturally-occuring beneficial ingredients and constitute the

major dietary source of lycopene. They contain higher levels of lycopene than any

other fruit or vegetable (Anon., 2005) and have been associated with decreased

risk of certain chronic diseases, such as cancer and cardiovascular disease

(Agarwal and Rao, 2000; Rivero et al., 2006). Since tomatoes undergo extensive

processing and storage before being consumed, researchers have studied the

stability of lycopene in tomato under processing and storage conditions. Results

indicate that lycopene present in fresh tomatoes and tomato products, is stable,

stays bioavailable and acts as an in vivo antioxidant providing protection against

lipid, protein, and DNA damage (Agarwal et al., 2001). The presence of dietary

lipids and heat during tomato processing also presented a positive effect resulting

in the higher release of lycopene and easier absorption by human body

(Porrini, 2003).

To have a beneficial effect on the human body and to prevent certain diseases,

the suggested daily dosage of lycopene is of 10 to 50 mg per day for adults.

Since lycopene is valued at $100 per mg, supplements would be too expensive

for most people to afford. As presented in Table 1.1, eating raw or processed

tomatoes represent the easiest and cheapest way to get the recommended

lycopene dosage in ones daily diet (Anon., 2005). Most importantly, one should

know that it is impossible to separate with certainty the effect of vitamin C and

lycopene in tomato consumption, since tomato is also a good source of vitamin C

(Porrini, 2003). A single carotenoid or a single phytonutrient may have a small

beneficial effect, but when they are combined, they often show a synergistic

effect (Levy, 2003). The emphasis should then be on the consumption of the

whole fruit rather than a single component, since food components work in

concert.

8

Table 1.1 : Ripening index values for tomato fruits at different color stages.

Adapted from Lopez Camelo and Gomez, 2004.

Product

Lycopene

(mg/100g) a Serving size b Lycopene

(mg/serving)

Tomato juice 9.3 240 mL 22.9

Tomato ketchup 17.0 15 mL 2.9

Tomato paste 29.3 30 g 8.8

Tomato soup 10.9 245 g 13.1

Tomato sauce 15.9 60 g 9.6

Fresh tomatoes c 12.5 148 g (1 medium) 18.5

a USDA-NCC Carotenoid Database for U.S. Foods 1998

b FDA Reference Amounts; Guidelines for Voluntary Nutrition Labeling of Raw

Fruit, Vegetables and Fish, Database Updated April 1, 2008.

c Agarwal et al. 2001

9

1.3.3. TOMATO PRODUCTION

Global tomato production (processing and fresh) has increased by 291% from

1961 to 2002 (FAS/USDA, 2003). World tomato production was about 100 million

tons of fresh fruits in 2004, grown in 144 countries (FAOSTAT Database, 2004).

In North America, California is the largest tomato producer with

11.7 million tons yr-1, followed by Ontario with a production of over

0.5 million ton yr-1 (Anon., 2005). Worldwide, China is becoming the largest fresh

tomato producer with 25.9 million tons yr-1 which represents about 25% of the

worlds tomato production. The United States is the second leading producer,

with 95% of production occurring in California (Anon., 2004).

Tomato is the second largest US fresh vegetable export. The top fresh tomato

exporters are Spain, Mexico, Canada, United States, Italy, France and Turkey.

Canada is the second most important supplier of fresh tomatoes to the United

States after Mexico (Anon., 2004). On the other hand, Italy is the world leader in

canned tomato exports, with approximately 80% of the world market. Chinas

exports of tomato have grown over the last decade and China has become the

second largest producer of tomato paste.

Tomatoes are grown commercially across the world and represent one of the

leading fruit productions. But tomatoes are also an important part of home-grown

gardens. In the US, it is estimated that 35 million backyard gardens grow

tomatoes (Cox, 2001).

1.4. PROBLEM STATEMENT

Since tomatoes are consumed in many countries, it is obvious that they must be

regarded as a part of a comprehensive strategy to prevent cancer through diet

and contribute to better human health worldwide. There is epidemiological

evidence that an increase in intake of tomatoes decreases the risk of certain

10

cancer and none of the studies reviewed showed adverse effects of high tomato

intake or high lycopene levels (Giovannucci, 1999; Dwyer, 2003).

Compared to 20 years ago, Canadians now eat 10.9% more fresh vegetables

and 10.2% more fresh fruits (Anon., 2008). Considering that 50% of all cancer

have been attributed to diet (Agarwal and Rao, 2000), the populations

awareness of this fact incites people to seek fresh produce exempt of chemical

preservatives.

Preservation methods free of chemicals have been investigated to prevent rotting

of fruits and vegetables through handling and storage. In this light, some physical

treatments have been studied and it was observed that, along with preventing

produce deterioration, these treatments can enhance beneficial nutrients and

nutraceutical substances in the treated produce. More work has been done on

tomatoes to improve their beneficial substances, such as lycopene. But physical

treatments, like UV and heat treatments used as surface sterilisation treatments,

are not easy to apply uniformly. The response to these treatments is also not

uniform.

Hyperbaric treatment is not a surface sterilising treatment but it has the

advantage of being uniform. It can be used to create a hormic stress to the

commodity being treated. The response reaction to a hormic stress would be a

defence reaction that can enhance beneficial nutrients and nutraceutical

substances in the treated produce. A hypothesis is being proposed that

hyperbaric treatment can enhance quality attributes of fresh tomatoes.

The overall purpose of the current study investigates some unique and innovative

features for handling fresh produce.

11

CHAPTER 2

2. OBJECTIVES

2.1. HYPOTHESIS

The hypothesis of this study is that hyperbaric pressure treatment can affect the

physiological development of freshly harvested fruits and vegetables and hence

modify their quality attributes.

2.2. MAIN OBJECTIVES

The main objectives of this research are:

To conceptualize, design and build a dynamic respirometer that can be used for hyperbaric treatments on fresh horticultural produce. The set up

should resist pressures up to 9 atmabs, record environmental conditions

such as temperature, O2 and CO2 concentrations, control gas flow rate,

record, in real time, respiration rate and respiratory quotient.

To measure the effect of hyperbaric treatments on respiration rate and respiratory quotient, of tomato fruit.

To evaluate the effect of hyperbaric treatments on quality attributes of tomato fruit.

To determine the optimal operational parameters of the system to effectively use hyperbaric treatments as a postharvest treatment on tomato fruit.

12

CHAPTER 3

3. LITERATURE REVIEW

3.1. INTRODUCTION

Fruits and vegetables are an important part of healthy eating habits. Consumer

demands for fresh fruits and vegetables of high quality, exempt of chemical

preservatives, and with good or improved nutritional properties incited the

industry to improve existing technologies and have lead to many research efforts

on novel technologies (Garcia and Barrett, 2002). However, the development of

new food processing technologies presents a variety of challenges related to

consumers perception, acceptance and purchasing behaviour. In order to

improve expected consumer appreciation and increase the chances of their

eventual acceptance, novel technologies should improve the sensory quality of

the food and be presented to consumer with factual information and clear

statements about their safety and benefits (Cardello, 2003).

Many studies reported include the occurrence of natural disease resistance in

fruits and vegetables. Some natural disease resistance seems to be induced

through external factors and others tend to be induced by the defence

mechanism of the plant (Terry and Joyce, 2004). The enhanced protection of

host plant tissue is an important factor in the development of new postharvest

technologies. This concept was defined by Luckey (2003) as plant hormesis

which involves the stimulation of a beneficial plant response by low or sub-lethal

doses of an elicitor/agent, such as a physical stress.

Physically-induced resistance by treatments such as heat, ionising radiation, UV

irradiation and pressure has received increasing attention over the recent years.

The primary mode of action of these treatments is disinfection of the commodity.

In some cases, the physical stress also induced resistance against future

13

infection (Terry and Joyce, 2004) and enhanced the production of beneficial

substances in the treated commodity (Luckey, 2003).

One should not underestimate the public concern over biotechnology. Some new

methods, such as genetically modified organisms or irradiation, are not well

received by consumers as they are considered potentially risky technology when

applied to human food. The lack of information available makes the public fearful

about possible unknown and unforeseen side effects (Cardello, 2003).

3.2. RESPIRATION RATE

Respiration is the process by which all fresh fruits and vegetables use their

carbohydrates, proteins and fats to transform oxygen into carbon dioxide.

Generally, as respiration occurs, the commoditys reserves are exhausted and it

results in reduced food value. The rate of deterioration of the commodities is

proportional to the respiration rate. Ethylene is a natural organic compound

affecting plant metabolism. This hormone regulates growth, development and

senescence. Generally, ethylene production increases with maturity at harvest

and with various physical stresses, such as bruises, cuts, disease incidence, high

temperatures and water (Kader, 2002). To preserve fresh fruits and vegetables

for long periods, it is important to reduce the respiration rate and reduce the

ethylene production. Many storage techniques induce a reduction in the

respiration rate.

Horticultural crops are classified according to their respiration rate (Kader, 2002).

The classification proposed a range from very low to extremely high respiration

rate, measured for different commodities under a 5C environment. Respiration

rate is presented as mL CO2 kg-1 h-1 or mg CO2 kg-1 h-1.

3.2.1. RESPIRATION DEFINITION

The respiration of fruits or vegetables is a biochemical reaction by which complex

substrate molecules like carbohydrates, proteins and fats are broken down into

14

simpler molecules such as CO2 and H2O. Along with this reaction, energy and

intermediate molecules are produced (Kader, 2002). Normally, when the

respiratory quotient is equal to 1, the respiration process can be represented by

the following Eq. 3.1.

molekcalOHCOOOHC /686666 2226126 +++ (3.1)

In this case, the respiratory process releases as many molecules of CO2 as O2

molecules were consumed. The rate at which the commodity uses oxygen to

consume carbohydrates is called the respiration rate and is dependent on the

metabolic activity. Respiration rate is presented in Eq. 3.2 (Lencki et al. 2004).

timecommodityofkgconsumedOorevolvedCOofvolumeratenRespiratio =

22

(3.2)

3.2.1.1. RESPIRATION DEFINITION

Horticultural commodities are classified according to their respiration rate and

pattern during maturation and ripening. There are two large classes of produce:

climacteric and non-climacteric. Climacteric fruits show an increase of CO2

production during ripening and non-climacteric fruits show no change in their

generally low CO2 production during ripening (Kader, 2002). Tomatoes are

climacteric fruits. They are considered to have a moderate respiration rate with

values varying between 10-20 mg of CO2 kg-1 h-1. During the climacteric rise of

respiration, tomato fruit soften, the yellow color intensifies (loss of chlorophyll and

increase in carotenoids) and fruit aroma (volatiles) increases. The peak of

respiration rate usually represents the time at which tomatoes are considered

ripe for consumption. Afterwards, respiration gradually decreases as the fruit

senesces.

Respiration rate varies among commodities but also within commodities. The

maturity of a plant at harvest also influences the respiration rate and commodities

harvested during active growth have high respiration rates (Saltveit, 2005).

15

Respiration rate is tightly related to the metabolism rate of the fruit or vegetable

and is generally proportional to the rate of deterioration (Kader, 2002).

3.2.1.2. MONITORING METABOLIC ACTIVITY

Since measuring respiration is a non-destructive way of monitoring the metabolic

and physiological state of the produce, it can be used to evaluate the stored fruits

and vegetables response after harvest. It provides information on the loss of

substrate, the synthesis of new compounds and the release of heat energy

(Saltveit, 2005). Some climacteric fruit, like tomatoes, are harvested prior to

maturity. The storage facilities have to be optimized to allow the commodities to

reach their best quality through respiration, like the synthesis of pigments

(lycopene and -carotene in tomatoes) and volatiles, the loss of chlorophyll and the conversion of starch to sugar for sweetness (Saltveit, 2005).

3.2.2. RESPIRATION QUOTIENT DEFINITION

To evaluate the respiration process and provide an indication of metabolic

activity, it is necessary to determine the ratio between the amounts of CO2

produced (Rx) over the amount of O2 consumed (Ry) by the plant material. This

ratio is referred to as the respiratory quotient (RQ) (Plasse, 1986; Saltveit, 2005).

consumedOproducedCO

RyRxRQ

2

2==

(3.3)

Where:

Rx = CO2 produced, %;

Ry = O2 consumed, %.

Both must be given in the same units, either moles or volume of gas, at the same

temperature and pressure.

With regards to the substrate being oxidized, RQ values for fresh commodities

may range from 0.7 to 1.3 for aerobic respiration (Saltveit, 2005). If the

16

respiratory process is normal and sugars are metabolized, RQ should be equal to

one. RQ values greater than one indicates that the organism is burning

carbohydrates to produce fat or there is oxygenated substrate utilization in

respiration, such as organic acids (proteins). A RQ value less than one may

indicate several possible situations, but it generally indicates that the oxidation

reaction is not complete (Plasse, 1986) or that the lipids (fats) are aerobically

respired (Saltveit, 2005). A very high value of RQ would indicate an anaerobic

process (Saltveit, 2005).

3.2.3. RELATIONSHIP BETWEEN RESPIRATION RATE AND

RESPIRATION QUOTIENT AND THEIR EFFECT ON PRODUCT

METABOLISM

Metabolic activity is an important factor to determine the rate of deterioration of

the harvested fruit or vegetable. As metabolic activity increases the physiological

state of the tissues changes and may accelerate senescence and ripening.

Reducing the respiration rate to the minimum that still permits normal cellular

function will delay ripening and increase the produces shelf life (Kader, 2002).

3.2.4. ENVIRONMENTAL FACTORS AFFECTING RESPIRATION RATE

AND RESPIRATION QUOTIENT

There are many factors affecting respiration including light, chemicals, radiation,

water, growth regulators and pathogens. But the most important factors to

consider are temperature, atmospheric composition and physical stress (Saltveit,

2005).

Temperature is the leading factor because it has a profound effect on the rates of

biological reactions in the commodities. The rate at which the respiration process

takes place is directly related to temperature: the higher the temperature the

higher the respiration rate. Its effect leads to overactive respiration at high

temperatures causing phytotoxic symptoms and even complete tissue collapse

(Saltveit, 2005). On the other hand, it may induce metabolic disturbance, even

17

physiological injury, when the temperature of storage is too low (Plasse, 1986).

Chilling stress may induce dramatic increases in respiration rate as the

commodity is returned to a non-chilling temperature. It reflects the cells efforts to

detoxify the metabolism and repair damages to membranes and other sub-

cellular structures (Saltveit, 2005).

Many conservation techniques rely on the low availability of oxygen in the

atmosphere to reduce the metabolic activity, as reflected by a reduction in starch

degradation and sugar consumption, of the stored produce (Plasse, 1986). Most

fruits and vegetables respond to a reduced oxygen concentration. The primary

metabolic response to low O2, between 1 and 3 kPa, is a general metabolic

suppression through the inhibition of respiration. The secondary metabolic

response to low O2, around 6 kPa, is the suppression of ripening through the

inhibition of ethylene action (Mir and Beaudry, 2001). Even if the produce

metabolism responds to low O2, reduced O2 has not been widely used for

storage of fruits which are highly susceptible to decay, like tomato and blueberry.

Low O2 atmospheres are limited by the development of decay since O2 partial

pressures have little effect on decay organisms (Mir and Beaudry, 2001).

Increasing the CO2 level around commodities also reduces respiration, delays

senescence and retards fungal growth (Saltveit, 2005). The effect of CO2 on

respiration relies on the inhibition of some enzymatic activities and the decrease

in the synthetic reactions of ripening (Plasse, 1986). Carbon dioxide is a soluble

gas. As its concentration increases in the storage atmosphere, the quantity

dissolved or combined with other constituents also increases. The effect that

these changes in gas concentration have on the respiration rate differs between

different types of produce (Plasse, 1986). For example, the respiration rate of

tomato does not slow down until the CO2 concentration in the atmosphere gets

up to 9%. Also, the oxygen level can decrease to 12% without having any effect

on metabolic activity of the tomato (Henig and Gilbert, 1975).

18

Physical stresses are indirect, secondary factors, which have an important impact

on respiration and may cause a substantial rise in respiration rate, often

associated with an increased ethylene evolution (Saltveit, 2005). These factors

stimulate respiration in an indirect way and their effects are not readily

observable. Physical stresses are encountered prior to storage, such as water

stress, heat stress, shortage or excesses in nutrients, and other preharvest

horticultural practices. Those factors can induce physiological or pathological

disorders to the stored commodity, such as the inhibition or the promotion of

senescence or a decrease in the rate of degradation (Fennir, 1997).

3.2.5. RQ VALUES AND THEIR SIGNIFICANCE

The respiration rate and respiration quotient are very closely related. When the

respiration process is normal and sugars are metabolized, the commodity

undergoes robic respiration. For example, RQ value recorded in an open

steady state system with atmospheric oxygen levels would present a fairly stable

RQ curve, slightly rising over time, as the commodity consumes its

carbohydrates. Initial values of RQ should range between 0.8 and 0.9 and can

rise to values up to 1 within hours. But these values are dependent on the

principal substrate that the plant is using in the respiratory process and can range

from 0.8 to 1.33 with fats or organic acids, respectively (Lencki et al., 2004). At

some point, the commodity will have used all of its resources and can no longer

consume oxygen. Oxygen available in the commodity will drop below the critical

value and induce fermentation. The respiration process will become anrobic

and starts producing more carbon dioxide. From that moment, RQ values present

a drastic change and start going up. This transition zone between robic and

anrobic respiratory processes is referred to as the extinction point (EP). This

term was first proposed by Thomas and Fidler (1933). It was also considered by

Turner (1951) as the lowest concentration of oxygen at which the RQ remains

about 1. The definition was further redefined as the lowest concentration of

oxygen at which alcohol production ceases (Kubo et al., 1996). From the EP,

carbon dioxide production increases and ethanol accumulates, inducing off-

19

flavours and tissue breakdown in the commodity. Previous results have

demonstrated that recording the oxygen and the carbon dioxide concentration in

a storage facility provides information on RQ and allows the determination of the

EP (Kubo et al., 1996). RQ values are rarely measured in experiments (Lencki,

2004); however, the extinction point, associated to RQ, is the most efficient way

to determine the transition between robic and anrobic respiration and predict

how long the commodity can be stored under specific conditions before

irreversible physiological damage is observed (Kubo et al., 1996).

Beaudry (1993) presented values of RQ based on different partial pressures of

oxygen and carbon dioxide on blueberry (Vaccinium sp.) fruit. At retail

temperature, 15C, RQ values increased at CO2 partial pressure above 20 kPa.

Partial pressures between 15 and 20 kPa enhanced storability, but those above

25 kPa were injurious. Beaudry (1993) presented the EP as the breakpoint or

the O2 lower limit where the oxygen partial pressure causes a 20% change in

the RQ relative to the aerobic RQ.

RQ values between 0.85 and 1.10 were maintained for periods up to 30 days.

Large swings in RQ are not typical and should be examined more closely and

questioned (Lencki, 2004).

3.2.6. METHODS TO MEASURE RESPIRATION RATE AND RQ

Different techniques are available to determine respiration rate. It can be

evaluated by measuring one or many of the following constituents: water

production, loss of substrate, loss of O2, increase in CO2 concentration or the

production of heat (Saltveit, 2005). The most common method is to measure the

CO2 released and the O2 uptake with either a static (closed chamber or closed

loop) or a dynamic system (open chamber or open loop). The static system

consists of placing commodities in a sealed container and measuring the CO2

increase in time. The dynamic system allows a flow of air to pass through the

commodities at a known rate. After the system reaches equilibrium, the

difference in gas concentration between the inlet and the outlet is measured. The

20

production rate is calculated by multiplying the difference in concentration by the

flow rate and dividing by the total weight of the commodity (Saltveit, 2005). The

dynamic system has an advantage over the static system since there are no

effects of gas accumulation. An open steady-state system is independent of the

loading and the produce pH as opposed to an unsteady-state closed chamber

(Lencki, 2004). RQ is simply obtained by dividing RRco2 by RRo2.

3.3. PHYSICAL TREATMENT

3.3.1. HEAT

Mild pre-storage heat treatment has been used for insect control and has been

proven effective against many storage diseases and physiological disorders

(Terry and Joyce, 2004), and shown to improve the eating qualities of stored

fruits and vegetables (Mulas and Schirra, 2007), and even to protect certain

phytochemicals like the red colour pigments in postharvest tomatoes, melons and

mangoes (Fallik, 2004). Heat treatments can be applied through vapour heat, hot

water dipping, or very short water rinse and brushing (Terry and Joyce, 2004).

3.3.1.1. THERMOTOLERANCE

Studies on the thermotolerance of different fruits are summarised in Lu et al.

(2007). Heat treatments enable fruits and vegetables to develop resistance to

injuries caused by low-temperatures. Tomatoes submitted to 38C air for 2-3

days were then stored for up to a month at 2C without developing chilling

injuries (Lurie and Sabehat, 1997). This beneficial effect was also observed on

pomegranate (Punica granatum L.), peach (Prunus persica (L.) Batsch), orange

(Citrus sinensis (L.) Osbeck) and avocado (Persea sp.) (Lu et al., 2007). On

the other hand, exposure to inappropriate heat can cause damage. Tomatoes

were found to be very sensitive to temperatures over 38C. Treatment with a

temperature of 42 or 46C for 24 hours caused both external and internal

damage to the fruit (Lurie and Sabehat, 1997). To be beneficial, heat treatment

needs to be well understood with respect to the heat-damage tolerance of the

21

species which could change within 1 to 2C, the cultivar, the harvest maturity, the

growing conditions and handling methods (Lu et al., 2007).

3.3.1.2. EFFECTS ON DISINFECTION AGAINST HUMAN

PATHOGENS

In the last couple of years, cantaloupes and melons (vars. of Cucumis melo),

leafy vegetables and tomatoes were largely linked to foodborne illness in North

America (Delaquis and Austin, 2007). Most of the outbreaks were due to

contamination with human pathogens like Salmonella, E. coli and Listeria.

Thermal treatments directed at the surface of the produce were an attempt to

properly eradicate any pathogen on the produce surface.

3.3.1.2.1. CANTALOUPE AND MELONS

The immersion of cantaloupes in water at 76C for 2-3 min did reduce

Salmonella enterica but did not completely eradicate inocula (Annous et al.,

2004). The quality attributes of the fruits were not adversely affected and fungal

decay rates and overall microbial populations were lowered. Immersion in water

at temperatures up to 96C for 2 min were also tested and compared to

untreated fruits to determine the efficacy of heat as a pasteurizing treatment

(Ukuku, 2006). In that particular study, Salmonella grew faster on the

cantaloupes that had received the heat treatment. It was concluded that sanitized

produce are susceptible to recontamination if exposed to human bacterial

pathogens during subsequent handling.

3.3.1.2.2. LEAFY VEGETABLES

Heat treatments can help control and delay the appearance of quality defects

that limit the shelf-life of fresh-cut lettuce. Immersion in chlorinated solution in the

range of 47 to 50C inhibits phenylpropanoid metabolism and delay the

appearance of edge-browning (Delaquis et al., 2004). However, pathogens have

been found to grow at a faster rate on heat-treated compared to conventionally-

22

processed fresh-cut lettuce (Li et al., 2001; Delaquis et al., 2002). The same

phenomenon was reported on broccoli (Brassica oleracea L., Italica group) florets

and cut green beans (Phaseolus vulgaris L.) that have been immersed in water at

52C for 90 seconds prior to packaging (Stringer et al., 2007).

3.3.1.2.3. TOMATOES

Tomatoes are prone to human pathogen contamination during production, from

the planting, flowering, to the harvesting period. It was recognised that

Salmonella can survive long periods on the fruit and plant surfaces. Bacterial

infiltration can occur through the stem or flower prior to harvest (Guo et al.,

2001), and post harvest through stem, scar and abrasion or puncture injuries of

the thin skin (Yuk et al., 2007). Contamination can also occur through the stem

scar by the immersion of warm fruits in water of lower temperature (Wei et al.,

1995). Heat treatments at 50C and up to 60C for short periods were tested on

fresh tomatoes. The treatments did improve the storage stability of tomatoes but

were marginally effective against human pathogens E. coli or Salmonella spp.

(Delaquis and Austin, 2007).

Heat treatments seem inappropriate for the disinfection of fresh fruits and

vegetables to be stored before being processed or sent to the consumer market,

and for fresh-cut produce prior to packaging (Delaquis and Austin, 2007). Even

though heat treatment has been proven to be beneficial in terms of crops

physiology and to be efficient on the control of some insect and fungal invasions,

the non-uniformity and slow rate of heat transfer through the fruit or vegetable, by

hot air or water, are probably the major obstacles to the industrialisation of heat

treatments (Lu et al., 2006).

3.3.2. UV-C

Short-wave ultra violet light, UV-C ranging between 190 and 280 nm wavelength,

have been used as physical methods to control postharvest diseases (Wilson et

al., 1997). The most effective wavelength to produce a germicidal effect is

approximately 260 nm (Shama, 2005). Although high dosage of UV light is

23

generally harmful to living systems, low doses can induce disease resistance,

slow down ripening and improve quality attributes of horticultural crops (Charles

and Arul, 2007). As heat shock or other physical stress, UV light alters the

chemistry of plants and in some cases enhances the nutraceutical potential in the

plant (Shama and Alderson, 2005). Studies have reported changes in the

physiological compounds of the irradiated fruits as it increased their levels of

phenols, flavonoids and phytoalexins (Ben-Yehoshua, 2003).

3.3.2.1. EFFECTS ON DISEASE

Effective control of several pathogens was achieved by low-doses of UV

irradiation prior to storage. Low dosage of irradiation, ranging from 0.25 to

8.0 kJ m-2, has been found to control many storage rots (Terry and Joyce, 2004).

However, UV light is only effective for disinfection of the surface and it has very

low penetrability into the solid material. Surfaces are to be smooth and exempt of

impurities (Shama, 2005). From most studies, it is recognised that the reduction

of disease incidence in the UV-C treated commodities is due to the enhancement

of the natural resistance of the product (Charles and Arul, 2007). Germicidal

effect of UV-C light is essentially limited to the time of exposure to the UV source

ranging from fraction of seconds to tens of seconds. It is considered a direct

effect. The hormetic effect of UV-C treatment occurs after exposure for

germicidal treatment, at periods of time ranging from hours to days (Shama,

2007).

3.3.2.2. HORMESIS EFFECTS IMPROVEMENTS OF QUALITY

ATTRIBUTES

3.3.2.2.1. POSITIVE CHANGES

Hormetic UV doses range from 0.125 to 9 kJ m-, with respect to the crop variety.

For most commodities, a single dose at low dosage is sufficient but others

require a range of doses. UV-C light treatment improved firmness of strawberry,

peach, apple (Malus domestica Borkh.), peppers (Capsicum annuum L.) and

tomato (Charles and Arul, 2007) and it delayed the colour changes of peppers

24

(Vincente et al., 2005), broccoli (Costa et al., 2006), and tomato (Charles and

Arul, 2007). All these attributes contribute to an increase in shelf-life. UV-C also

has an impact on the respiration pattern of some fruits and vegetables. Tomato

ripening and senescence were delayed by a hormic dose of UV-C (200-280 nm,

3.7 kJ m-) but a higher dosage (24.4 kJ m-2) impaired ripening and caused

abnormalities in fruit development (Maharaj et al., 1999). In addition, the

respiration rate and the ethylene production were also reduced. UV also induced

rapid accumulation of photooxidation products as the plants react by stimulating

their defence mechanisms against oxidation (Shama and Alderson, 2005). It

showed particularly promising results in increasing the resveratrol content in table

grape (Vitis vinifera L.) (Cantos et al., 2001).

3.3.2.2.2. ADVERSE EFFECTS

UV dosage induced skin discolouration in tomatoes, browning and drying in

strawberries (Fragaria ananassa Duchesne) and mangoes (Mangifera indica

L.), brown rot in peaches, premature ripening of mangoes and a prolonged

exposure of tomatoes accelerated ripening and senescence (Shama and

Alderson, 2005). UV rays are also known to destroy vitamins C and B but

enhance vitamin D production. They cause oxidative deterioration of oils and fats

leading to rancidity and cause browning of some vegetables (Shama, 2005).

Further, UV exposure had a negative impact on carotenoids, especially lycopene,

in tomatoes (Charles and Arul, 2007; Jagadeesh et al., 2009) and pepper

(Vincente et al., 2005). Considering these results, UV-C might not be a valuable

treatment to enhance the beneficial properties of tomatoes, as lycopene is a

highly valued phytochemical mostly present in tomatoes.

3.3.2.3. EFFICACY OF UV TREATMENT

UV-C treatment needs to be adapted to a particular commodity, after thorough

investigation. Each variety, with respect to the time of harvest and the intended

target, needs a specific treatment length and intensity. It is therefore important to

determine the appropriate dosage to induce protection and not deteriorate fresh

25

produce (Shama, 2007). Further, UV-C treatment is not a systemic treatment and

its efficacy is very much dependent on the geometry and skin type of the

commodity (Charles and Arul, 2007). Disease resistance will only be induced in

tissue directly exposed to rays (Shama, 2007). Some produce are very difficult to

treat, like grapes, as the exterior will get an overdose before the inside gets the

needed dosage.

One should also consider, prior to commercialisation of any system, the danger

that UV-C rays exposure represent on human health and be aware that special

considerations have to be given to protect workers (Shama, 2007).

3.3.3. PRESSURE

Pressure treatment is one of the techniques that can meet the consumer demand

in aiding the supply of high quality foods that are not genetically modified or

irradiated (Cardello, 2003) and are microbiologically safe with an extended shelf-

life (Patterson, 2005). Pressure treatment consists of applying pressure beyond

atmospheric pressure to fresh or processed foods (Anon., 2000; Ahmed and

Ramaswamy, 2006). Exposure to the pressure can range from a millisecond

pulse to a treatment time of over 1200 s (Anon., 2000). These treatments offer

homogeneity as they act instantaneously and uniformly throughout the entire

mass of food, independently of its size, shape or composition (Ahmed and

Ramaswamy 2006). Considering the large scale of pressures applied to produce,

pressure treatments need to be categorized (Fig. 3.1). Treatments can be divided

into two categories: low pressure treatment that can be hypobaric and/or

hyperbaric, and high pressure. Low pressure treatment (0 to 1 MPa) is applied to

fresh produce and high pressure (above 100 MPa) is generally applied to

processed food. In the range of 1 MPa and 100 MPa, pressure might be too high

to treat pressure sensitive fresh horticultural crops without damaging them, and

too low to have a significant effect on microorganisms reduction and enzymes

inactivation.

26

Figure 3.1 : Representation of pressure range treatment and the type of

produce on which the treatment can be applied.

Pressure Treatment

Hypobaric0-0.1 MPa

Hyperbaric0.1-1 MPa

High> 100 MPa

PressureAtmospheric pressure

Fresh horticultural crop Processed food

Absolutezero pressure

Pressure Treatment

Hypobaric0-0.1 MPa

Hyperbaric0.1-1 MPa

High> 100 MPa

PressureAtmospheric pressure

Fresh horticultural crop Processed food

Absolutezero pressure

27

3.3.3.1. HIGH PRESSURE PROCESSING (HPP)

High pressure processing (HPP), also referred to as high hydrostatic pressure

(HHP) or ultra high pressure (UHP) processing, consists of subjecting liquid and

solid foods, with or without packaging, to pressures between 100 and 800 MPa

(Anon., 2000), and even up to 1200 MPa (Ahmed and Ramaswamy, 2006).

Exposure to the pressure can range from a millisecond pulse to a treatment time

of over 1200 s (20 min) (Anon., 2000).

There is an increase in interest around the world in the application of HPP

treatment for food because of the advantages of this technology over other

processing and preservation methods. Until now, thermal processing was the

most widely used technology since it allows efficient inactivation of both

pathogenic and spoilage microorganisms. Unfortunately, these treatments alter

organoleptic and nutritional qualities of the food (Ludikhuyze et al., 2003). Many

studies have demonstrated that HPP can (1) significantly or totally inactivate

micro organisms and (2) increase functional and nutritional retention of

ingredients (Estrada-Girn et al., 2005). High pressure processing offers many

advantages but the main drawback is the high capital cost of the commercial-

scale equipment (Ahmed and Ramaswamy, 2006).

3.3.3.1.1. EFFECTS ON PATHOGEN

High pressure processing has been used in the production of processed fruits

and vegetables primarily to reduce micro-organisms and inactivate enzymes that

would, upon storage, cause deterioration of the product or endanger consumers

health. Yeasts, moulds and vegetative cells are pressure sensitive and can be

inactivated by treatments between 300 and 600 MPa. On the other hand,

bacterial spores are highly resistant to pressure treatment and over 1200 MPa is

necessary for their inactivation. (Garcia and Barrett, 2002). Bacterial spores,

because of their extreme resistance to pressure, are sometimes very difficult to

control by a unique pressure treatment (Ludikhuyze et al., 2003).

28

It was demonstrated that HPP treatment can inactivate yeasts (Saccharomyces

cerevisiae and Listeria innocua) on diced apples, and whole processed

blueberries, strawberries and grapes (Chauvin et al., 2005). No significant effect

was observed between pressures of 300 MPa for 20 to 100 s and 375 MPa for

30 to 180 s at 21C. Both treatments were suitable to inactivate the micro organisms and preserve the fresh appearance and texture of the fruits.

Vegetative cells were reduced by six-fold in apple juice using a pressure of 200

MPa for 60 min or 300 MPa for 5 min (Voldrich et al., 2004). High pressure of 600

MPa at 20C was also applied to orange juice to reduce microbial load to a non-detectable level after a 4 week period of storage (Bull et al., 2004).

3.3.3.1.2. EFFECTS ON ENZYMES

Many studies tested the efficiency of HPP treatment on the control of enzymes

and pathogenic organisms in fresh fruits and vegetables and fresh fruit juices.

Natural enzymes in fruits and vegetables cause changes in colour, flavour,

texture and nutritive value; thus enzymatic reactions are a major problem. Some

enzymes can be inactivated at room temperature and low pressures whereas

others can withstand high temperatures and pressures (Ahmed and

Ramaswamy, 2006).

Heat treatments (high temperature and ultra high temperature), have been widely

used to kill pathogenic micro organisms, inactivate anti-nutritional substances,

promote certain sensory properties and increase storage life (Wennberg and

Nyman, 2004). But high temperatures are also partly responsible for the loss of

nutrients, such as minerals and vitamins, and the formation of off-flavours and

degradation of colour and texture (Lambert et al. 19