hiperbarica con -tomates
TRANSCRIPT
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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
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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
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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.
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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,
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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.
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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.
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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)
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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
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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).
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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
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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.
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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
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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,
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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.
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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.
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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
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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
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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.
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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.
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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
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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
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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).
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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
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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
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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).
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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-
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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
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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
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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-
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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
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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
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(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
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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.
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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
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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).
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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