 

 

LIBRARY
Michigan State
University

 

 

 

PLACE IN RETURN Box to remove this checkout from your record.
To AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

DATE DUE DATE DUE DATE DUE

 

JAN 0 9 2007

 

'011 0 013

 

 

 

 

 

 

 

 

 

 

 

 

6/01 c:/CIFIC/DateDue.965-p. 1 5

 

 

 

Effect of High Pressure Processing for Packaged Foods on the Mass Transfer and
Mechanical Characteristics of the Flexible Packaging Materials.

By

Cengiz CANER

A DISSERTATION

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

DOCTOR OF PHILOSOPHY

Department of School of Packaging

2002

ABSTRACT

EFFECT OF HIGH PRESSURE PROCESSING of PLASTIC PACKAGED
FOODS on THE MASS TRANSFER AND MECHANICAL
CHARACTERISTICS OF THE PACKAGE.

By

Cengiz CANER

High pressure processing (HPP) can be applied to either in bulk or prepackaged
food in ﬂexible or semi rigid packaging materials. Since the integrity of the package
during and after processing is of paramount importance, this study investigated the
effects of HPP on the barrier, mechanical, physical characteristics and sorption behavior
of selected ﬂexible structures.

In chapter 2 the “barrier properties” and in chapter 3 the “mechanical properties”
were compared for hi gh-pressure treated and non-treated pouches. After HPP, the
permeability, tensile properties and sorption behavior of the materials were evaluated.
Scanning electron microscopy (SEM), and scanning acoustic microscopy (C-SAM)
measurements were also taken to investigate the presence of micro defects in the ﬁlms.
Films used in this study were PET/SiOx/LDPE, PET/A1203/LDPE,
PET/PVDC/nylon/HDPE/PE, PE/nylon/EVOH/PE, PE/nylon/PE, metallized
PET/EVA/LLDPE, PP/nylon/PP, PET/EVA/PET and PP. Results showed that the
permeability of metallized PET was most severely affected by HPP. Permeability

changes in the other materials were small compared to metallized PET. Tensile properties

of the ﬁlms were not affected. However, physical damage to the metallized-PET ﬁlms
was identiﬁed by SEM and C-SAM analyses.

In chapter 4 the sorption of d-limonene was evaluated in both the polymeric
structures (PP, multilayer PE/nylon/EVOH/PE, and metallized PET/EVA/LLDPE) and
the food simulants, in both the HPP and untreated pouches as a function of time. Results
showed that d-limonene concentration, both in the polymers and in the food simulants for
pouches made of PP and (PE/nylon/EVOH/PE), was not signiﬁcantly affected by HPP.
However, the metallized PET/EVA/LLDPE showed a signiﬁcant difference in the
amount of d-limonene between HPP and control pouches. As expected, changes in
temperature signiﬁcantly affected the sorption behavior of all polymers. While PP and

PE/nylon/EVOH/PE ﬁlms retained d-limonene amount, the metallized-PET did not.

ACKNOWLEDGEMENTS

It is very meaningful to complete my PhD at the School of Packaging, MSU. First
of all, I want to express my sincere gratitude to Dr. Ruben Hernandez for his guidance
and advice as my advisor. He had never stooped giving good comments to improve this
dissertation. My deepest gratitude goes to my second advisor Dr. Bruce Harte for
guidance, permanent support and timely help during these past years. Special thanks to
my ex-advisor Dr Vergano from Clemson University for guidelines to opening door to
food packaging area. All I have learned from them will always remain in my mind. I
really appreciate their understanding, patience and support. Appreciation is also
expressed to Drs Tee Downes, Dr Susan Selke and Dr Jerry Cash for their serving my
guidance committee.

My deepest thanks to my Sponsor, the Turkish Ministry of Education, for giving
me an opportunity to conduct my graduate studies in the Clemson Univ. and MSU.

I thank the CFPPR for their support through my graduate program.

Many thanks to faculty staff and graduate students in the School of Packaging for
theirs help and friendship. I especially thank Rujide Uthaisombut, and Kiritika
Tanparanset, Manoch Sirinangam, Lee Youn Suk and Jong-Koo Han for their support
and friendship. Special thanks to Kadir Kizilkaya, Omer Ozel, and Savas Berber.

Finally my warmest and deepest appreciation should deﬁnitely be
extended to my dear parents (Mahmut Guzel, Hikmet) and lovely wife (Akgul CANER),

present and future, for their incomparable support and understanding.

IV

TABLE OF CONTENT

LIST OF TABLES ........................................................................................................... viii
LIST OF FIGURES ........................................................................................................... ix
INTRODUCTION ............................................................................................................. 1
OBJECTIVE ...................................................................................................................... 6
REFERENCES ................................................................................................................... 9
CHAPTER 1: LITERATURE REVIEW ..................................................................... 10
1.1. HIGH PRESSURE PROCESSING ........................................................................... 11
1.1.1. Batch HPP Technology ................................................................... 13
1.1.2. Semi-Continous HPP Technology .................................................. 15
1.2. CRITICAL PROCESS FACTORS ........................................................................... 15
1.2.1.1. Type of Microorganism ............................................................... 15
1.2.1.2. Temperature, Pressure Magnitude, and Holding Time ................ 16
1.2.1.3. Ratio of Pressurizing Fluid to Product in Vessel Chamber ......... 16
1.2.2.1. HPP Sterilization Product Cost .................................................... 16
1.3. FOOD PACKAGING AND HIGH PRESSURE PROCESSING ............................. 17
1.4. PACKAGING AND PROTECTION ........................................................................ 22
1.4.1. Plastic Structure as Food Packaging Materials ............................... 23

1.5. MASS TRANSPORT PHENOMENA AND FOOD/PACKAGING
INETREACTIONS .............................................................................................. 23
1.5.1 . Permeability ................................................................................... 25
1.5.1.1. Pressure Variable Method ................................................ 29
1.5.1.2. Isostatic Method ............................................................... 30
1.5.1.3. Quasi-Isostatic Method .................................................... 31
1.5.1.4. Water Vapor Transmission Rate Measurement ............... 31

1.5.1.5. Oxygen Transmission RateMeasurement ........................ 32

1.5.1.6. Carbondioxide Transmission RateMeasurement ............. 33
1.5.2. Sorption ...................................................................................................... 34
1.5.2.1. Henry's Law Sorption ....................................................... 35
1.5.2.2. Langmuir Sorption Isotherm ............................................. 35
1.5.2.3 Flory-Huggins Sorption ..................................................... 36
1.5.2.4 Dual-Mode Sorption .......................................................... 36
1.5.3. Migration ..................................................................................................... 37
1.6. FACTOR AFFECTING PERMEATION, SORPTION, AND MIGRATION
PROCESSES IN PACKAGE-PRODUCT SYSTEMS ........................................ 38
1.6.1. Composition Variables .................................................................... 39
1.6.1.1. Nature of Polymer ............................................................. 39
1.6.1.2. Nature of Permeant ........................................................... 40
1.6.2 Environmental and Geometric Factors ............................................ 41
1 .6.2. 1 .Temperature ....................................................................... 41
1.6.2.2. Relative Humidity ............................................................. 42
1.6.2.3. Packaging Geometry ......................................................... 43
1.7. MECHANICAL PROPERTIES ................................................................................ 43

1.7.1. Effect of External and Internal Factors on Mechanical Properties. 43

1.7.2. Tensile Properties ............................................................................ 45

1.7.2.1. Tensile Strength ................................................................ 46

1.7.2.2. Yield Strength ................................................................... 46

1.7.2.3. Percent Elongation ............................................................ 46

1.7.2.4. Modulus of Elasticity ........................................................ 47

1.7.2.5. Toughness ......................................................................... 47

REFERENCES ................................................................................................................. 48

vi

CHAPTER 2: EFFECT OF HIGH PRESSURE PROCESSING ON SELECTED

HIGH BARRIER LAMINATED FILMS USED FOR FOOD PACKAGING ........ 55
ABSTRACT ...................................................................................................................... 55
2.1 INTRODUCTION ...................................................................................................... 56
2.2 MATERIALS AND METHODS: ............................................................................... 57
2.2.1. High-pressure apparatus .................................................................. 60
2.2.2. Perrneance ....................................................................................... 60
2.2.3. Water vapor transmission rate ........................................................ 61
2.2.4. Oxygen transmission rate ................................................................ 62
2.2.5 Carbon dioxide transmission rate ..................................................... 62
2.2.6 Statistical analysis ............................................................................ 63
2.3 RESULTS & DISCUSSION ....................................................................................... 64
2.3.1 Oxygen permeance ........................................................................... 64
2.3.2 Water vapor permeance ................................................................... 68
2.3.3 Carbon dioxide permeance .............................................................. 72
2.4. CONCLUSIONS ........................................................................................................ 76
2.5. REFERENCES .......................................................................................................... 77

CHAPTER 3: STUDY OF HIGH PRESSURE PROCESSING EFFECTS ON
FLEXIBLE FOOD PACKAGING STRUCTURES BY MECHANICAL
ANALYSIS, SCANNING ELECTRON MICROSCOPY, AND ULTRASONIC

IMAGING ...................................................................................................................... 79
ABSTRACT ...................................................................................................................... 79
3.1 INTRODUCTION ...................................................................................................... 80
3.2. MATERIALS AND METHODS ............................................................................... 83
3.2.1. High-pressure apparatus .................................................................. 83
3.2.2. Scanning Electron Microscopy ....................................................... 84

vii

3.2.3. Scanning Acoustic Microscope ....................................................... 84

3.2.4. Tensile stress, strain, and modulus of elasticity .............................. 85
3.2.5. Statistical analysis ........................................................................... 86
3.3. RESULTS AND DISCUSSION ................................................................................ 88
3.4. CONCLUSIONS ...................................................................................................... 101
3.5 REFERENCES ......................................................................................................... 102

CHAPTER 4: THE EFFECT OF HIGH-PRESSURE FOOD PROCESSING ON
THE SORPTION BEHAVIOR OF FLEXIBLE PACKAGING POLYMERIC

ABSTRACT .................................................................................................................... 104
4.1 . INTRODUCTION ................................................................................................... 105
4.2. MATERIALS AND METHODS: ............................................................................ 109
4.2.1. Materials ................................................................................................... 109
4.2.2. Equipment ................................................................................................. l 10
4.2.2.1. High—pressure processor ............................................................. 110
4.2.2.2. Dynamic thermal shipper (DTS)/thermal desorption (TD)/ gas
chromatograph (GC) system .................................................................. 111
4.2.3. Methods ..................................................................................................... 111
4.2.3.1. Dynamic thermal stripping ........................................................ 114
4.2.3.2. Gas chromatography. ................................................................. 115
4.2.3.3. Determining d-limonene from plastic ﬁlm using a liquid
extraction method .................................................................................... 116
4.2.3.4. Statistical analysis ...................................................................... 117
4.3. RESULTS AND DISCUSSION .............................................................................. 117
4.3.1. Polypropylene (PP) ................................................................................... 117
4.3.2. PE/nylon/EVOH/PE .................................................................................. 121

4.3.3. Met-PET 12 um /30%VA EVA/LLDPE (Coated multilayer structure)... 124

viii

4.4. CONCLUSIONS ...................................................................................................... 131

4.5. REFERENCES ........................................................................................................ 132
CHAPTER 5: CONLUSION AND FUTURE WORK ............................................. 134
APPENDICES ............................................................................................................... 138

ix

LIST OF TABLES

CHAPTER 2:

Table 2.1. The composition of the test ﬁlms used in this study ................................. 59
CHAPTER 3:

Table 3.1. Composition of the test ﬁlms used in this study ....................................... 87
CHAPTER 4:

Table 4.1. Composition of the test ﬁlms used in this study. .................................... 110
Table 4.2. Thermal and ﬂow rate conditions used for the thermal stripper. ............ 115
Table 4.3. Conditions used for thermal desorption unit ......................................... 116
Table 4.3. The solubility parameters, * (J/cm’) and Sp-SL. ....................................... 125
Appendices

Table A1 Table A1: Analysis of LSMEAN S of the oxygen permeability (RxlO15 )
m3(STP)/m .s.Pa of the ﬂexible structures ............................................. 141

Table A2. Analysis of LSMEANS of the water permeability (RxlO'z) kg/m2.s.Pa of the
ﬂexible structures .................................................................................... 142

Table A3. Analysis of LSMEAN S of the carbon dioxide permeability (RxlO15 )
m3(STP)/m2.s.Pa of the ﬂexible structures. ........................................... 143

Table A4. Analysis of LSMEAN S of tensile strength (MPa) machine direction of the
ﬂexible structures .................................................................................... 144

Table A5. Analysis of LSMEAN S of tensile strength (MPa) cross direction of the ﬂexible
structures. ................................................................................................ 145

Table A6. Analysis of LSMEANS of % elongation machine direction of the ﬂexible
structures. ................................................................................................ 146

Table A7. Analysis of LSMEANS of % elongation cross direction of the ﬂexible
structures. ................................................................................................ 147

Table A8. Analysis of LSMEAN S of % modulus of elongation machine direction of the
ﬂexible structures. ................................................................................... 148

Table A9. Analysis of LSMEAN S of % modulus of elongation cross direction of the
ﬂexible structures. ................................................................................... 149

xi

LIST OF FIGURES

CHAPTER 1

Figure 1.1. A typical schematic view of the bathch high-pressure processing vessel for

a packaged food product 1) before pressure 2) during pressure. .............. 14
Figure 1. 2. A typical stress/strain curve for thermoplastic polymer. ............................... 47
Figure 1.3. Typical stress/strain curves obtained with plastic polymers polymer ............ 47
CHAPTER 2
Figure 2.1. Oxygen permeance of multilayer ﬁlms before and after HPP measured at
23°C. ......................................................................................................... 66

Figure 2.2. Oxygen permeance of multilayer ﬁlms before and after HPP measured at
23°C. ......................................................................................................... 66

Figure 2.3. Percent change in oxygen permeance of multilayer ﬁlms before and after
HPP measured at 23°C .............................................................................. 67

Figure 2.4. Percent change in oxygen permeance of multilayer ﬁlms before and after
HPP measured at 23°C. ............................................................................. 67

Figure 2.5. Water vapor permeance of multilayer ﬁlms before and after HPP
measured at 378°C ................................................................................... 70

Figure 2.6. Water vapor permeance of multilayer ﬁlms before and after HPP
measured at 378°C. .................................................................................. 70

Figure 2.7. Percent change in water vapor permeance of multilayer ﬁlms before and
after HPP measured at 378°C. ................................................................. 71

Figure 2.8. Percent change in water vapor permeance of multilayer ﬁlms before and
aﬁer HPP measured at 378°C. ................................................................. 71

Figure 2.9. Carbon dioxide permeance of multilayer ﬁlms before and after HPP
measured at 23°C. ..................................................................................... 74

Figure 2.10. Carbon dioxide permeance of multilayer ﬁlms before and after HPP
measured at 23°C ...................................................................................... 74

xii

Figure 2.11.

Figure 2.12.

CHAPTER 3

Figure 3.1.

Figure 3.2.

Figure 3.3.

Figure 3.4.

Figure 3.5.

Figure 3.6.

Figure 3.7.

Figure 3.8.

Figure 3.9.

CHAPTER 4

Figure 4.1.

Figure 4.2.

Percent change in carbon dioxide permeance of multilayer ﬁlms before
and after HPP measured at 23°C ............................................................... 75

Percent change in carbon dioxide permeance of multilayer ﬁlms before
and after HPP measured at 23°C ............................................................... 75

Tensile Strength (MPa) of plastic ﬁlms at machine direction before
(controls) and after HPP treatment at 45°C for 5, 10 and 20 minutes. ..... 92

Tensile Strength (MPa) of ﬂexible structure at cross direction before
(controls) and after HPP treatment at 45°C for 5, 10 and 20 minutes. ..... 93

Percent Stain of ﬂexible structure at machine direction before (controls)
and aﬁer HPP treatment at 45°C for 5, 10 and 20 minutes. ...................... 94

Percent Stain of ﬂexible structure at cross direction before (controls) and
after HPP treatment at 45°C for 5, 10 and 20 minutes. ............................. 95

Modulus of Elasticity (MPa) of ﬂexible structure at machine direction
before (controls) and after HPP treatment at 45°C for 5, 10 and 20
minutes. ..................................................................................................... 96

Modulus of Elasticity (MPa) of ﬂexible structure at cross direction before
(controls) and after HPP treatment at 45°C for 5, 10 and 20 minutes ...... 97

Scanning electron micrographs of PP/ Nylon-6/ PP, PET / A1203/ LDPE,
PET /SiOx/ LDPE, PET/PVDC/Nylon/HDPE/PP, PP/EVOH/Nylon/PP,
PE/Nylon/PP, PET/PVDC/EVA and PP ﬁlms before (controls) and after
HPP treatment at 45°C for 5, 10 and 20 minutes. ..................................... 98

Scanning electron micrographs of metallized -PET materials before
(controls) and after HPP treatment at 45°C for 5, 10 and 20 minutes ...... 99

Scanning acoustic micrograph of metallized -PET materials before
(controls) and after HPP treatment at 800 MPa 45°C for 10 minutes ..... 100

Flow sheet diagram indicating main steps of general sample preparation.
................................................................................................................. 1 12

Diagram indicating the two procedures followed to evaluating the sorption
behavior ................................................................................................... 114

xiii

Figure 4.3.

Figure 4.4.

Figure 4.5.

Figure 4.6.

Figure 4.7.

Figure 4.8.

Figure 4.9.

Figure 4.10.

Figure 4.11.

Figure 4.12.

Figure 4.13.

Figure 4.14.

Figure 4.15.

Concentration of d-limonene in PP ﬁlm contacting 10% ethanol FSL
treated at 800 MPa and 60 °C according to procedures A and B ............ 113

Concentration of d-limonene in PP ﬁlm contacting with 3% acetic acid
FSL treated at 800 MPa and 60 °C according to procedures A and B. 119

Concentration of d-limonene in FSL (10% ethanol) in PP ﬁlm treated at
800 MPa and 60 °C according to procedures A and B. .......................... 119

Concentration of d-limonene in FSL (3 % acetic acid) in PP ﬁlm FSL
treated at 800 MPa and 60 °C according to procedures A and B ............ 120

Concentration of d-limonene in PE/nylon/EVOH/PE ﬁlm contacting with
10% ethanol FSL treated at 800 MPa and 60 °C according to procedures A
and B. ...................................................................................................... 122

Concentration of d-limonene in PE/nylon/EVOI-I/PE ﬁhn contacting with
3% acetic acid FSL treated at 800 MPa and 60 °C according to procedures
A and B ................................................................................................... 122

Concentration of d-limonene in FSL (10% ethanol) in PE/nylon/EVOH/PE
ﬁlm treated at 800 MPa and 60 °C according to procedures A and B.. .. 123

Concentration of d-1imonene in FSL (3 % acetic acid) in
PE/nylon/EVOH/PE ﬁlm treated at 800 MPa and 60 °C according to
procedures A and B ................................................................................. 123

Concentration of d-limonene in Met-PET 12 um /30%VA EVA/LLDPE
ﬁlm contacting with 10% ethanol FSL treated at 800 MPa and 60 °C
according to procedures A and B ............................................................ 125

Concentration of d-limonene in Met-PET 12 um /30%VA EVA/LLDPE
ﬁlm contacting with 3 % acetic acid FSL treated at 800 MPa and 60 °C
according to procedures A and B. ........................................................... 125

Concentration of d-limonene in FSL (10% ethanol) in Met-PET 12 um
/30%VA EVA/LLDPE ﬁlm treated at 800 MPa and 60 °C according to
procedures A and B ................................................................................. 126

Concentration of d-limonene in FSL (3% acetic acid) in Met-PET 12 um

/30%VA EVA/LLDPE ﬁlm treated at 800 MPa and 60 °C according to
procedures A and B ................................................................................. 126

Coming up time for d-limonene using GC ............................................. 130

xiv

Introduction

Food preservation and protection is essential for delivering food to the consumer
in its best possible quality. The main aim of food processing methods is to achieve
desirable changes while preventing or retarding undesirable changes to the food. Food
can be preserved by thermal and non-thermal processes.

Thermal processing methods are widely used in the food industry to increase shelf
life and maintain food safety by employing heat to kill microorganisms (Palou et a1,
1999). In traditional thermal methods, food is subjected to a temperature of 60 to 100°C
for a few seconds to minutes (Barbosa-Canovas et a1, 1996). During this time period,
large amounts of energy are transferred to the food. This energy may trigger several
unwanted reactions in the food, leading to undesirable results such as: vitamin loss,
changes in sensory properties such as color and ﬂavor, odor, nutrient destruction, and
formation of undesirable substances, causing quality deterioration (Ohlsson, 1996;
Kimura, 1992). In an attempt to eliminate these thermal processing disadvantages, a
number of “non-thermal processing” techniques have been developed in the pursuit of
producing better quality foods (Hayashi, 1989; Mertens, 1993; Nachmanson, 1995). The
main driving force in the development of non-thermal processing methods for food
preservation is that food is keep at lower temperatures. Thus, the heat induced quality
deterioration is minimized (Campbell and Goddard, 1993; Hoover et al, 1989).
Techniques include high intensity pulsed electric ﬁelds, hurdle technology, radiation,
light pulses, ultrasonic, and high pressure techniques) (Knorr, 1994).

In the past few years there has been great interest in the use of non-thermal high

pressure processing (HPP) as an industrial technique for food preservation. A great
advantage of this technique is the minimal quality alteration compared to thermal
treatment (Farkas and Hoover, 2000). Combining high pressure with high temperature
can also inactivate spores. This process applies high pressure, 300 to 800 MPa, to the
foodstuff to reduce or eliminate microorganisms and deactivate enzymes by pure
mechanical action at relatively low temperature when compared with thermal processing
techniques. HPP uses hydrostatic pressure which is evenly distributed throughout the
product. As a result, the processing time does not depend on size and shape of the product
(Pre, 1992). Hydrostatic pressure does not create shear forces to distort food particles.
Today, high pressure processing of foods has become a commercial reality for processing
of certain food products; however, increased use of HPP for food and packaged food
should be discussed and considered (Mertens and Deplace, 1993; Palou et a1, 1999).
Examples of the applications are tenderization of beef, manufacture of food purees, jams
and jellies, and of marmalade from oranges, and milk. Packaged foods subjected to HPP
were found to retain most of their original texture, nutritional, and sensory quality
(Cheftel, 1992; Mertens and Knorr, 1992). These positive attributes may lead to wider
commercial applications of HPP for certain food products in the near future.

Liquid or solid food products can be hi gh-pressure processed either in bulk or
prepackaged in ﬂexible or semi—rigid packaging materials. Although food can be
processed in bulk followed by aseptic ﬁlling, the most efﬁcient procedure is to package
the products in sealed non-rigid containers before they are subjected to HPP, to prevent
subsequent recontarnination by microorganisms. In the latter case, the packaging

material together with the food is subjected to the action of high-pressure treatment.

Since the integrity of the package during and after processing is of paramount
important to secure the beneﬁts of this technique, selecting a suitable package is crucial
to the success of HPP. The package needs to withstand the compression forces generated
during high-pressure processing. It must also be ﬂexible and able to maintain its physical
integrity to prevent subsequent recontamination of the food by microorganisms (Anon,
1996; Cano et al, 1997). Metal cans or glass bottles are not well suited for HPP because
they deform irreversibly or tend to fracture, respectively. Similarly, paperboard-based
packages have limited application in HPP due to their lack of cohesion and tendency to
deform (Mertens, 1993).

Desirable characteristics of ﬂexible plastics such as light weight, clarity, good
processing and good sealing attributes, strength, barrier properties and low cost make
them widely used as packaging materials (Hernandez, 1996). Moreover, they are
typically used for the type of prepackaged foods that may be HPP treated (Nachmanson,
1995). Ideally, HPP should not affect to any degree the integrity of the packaging
structures. Recent research has demonstrated however, that this may not be the case for
some composite ﬂexible structures (Hayahsi, 1989).

A reversible response to compression of the whole package is crucial for success
in pressure treatment. Pressure causes the product to compress tri-dimensionally up to
12%, depending on the pressure level. The product must recover its initial volume after
the pressure is released. For the prepackaged product, the high compression forces also
act on the polymeric package reducing its volume. Packaging materials for HPP need to
have sufﬁcient ﬂexibility to compensate for the compression and volume reduction and to

prevent deformation (Sanchez et al, 1993). For these reasons, single or multilayer plastic

ﬂexible structures having signiﬁcant resiliency and elasticity are the best-suited
packaging materials for processing prepackaged foods by HPP (Knorr 1995). Although
HPP is a non-thermal treatment, molecular friction during high pressure generates enough
heat to increase the temperature of the food-package system. The temperature of
compressed water increases in the range of 2-3 °C for every 100 MP3 of the compression
(Ting et al, 2002). The increase in temperature also affects the package’s ability to adapt
to withstand the combined effect of rising temperature and decreasing volume during the
HPP treatment. Therefore, the package must be able to withstand pressure.

Lack of information on prepackaged high-pressure treatment has been a major
issues in using this technology commercially for prepackaged food products. Effect of
high pressure processing on packaging structures may impact the product quality, safety
and shelf life. An understanding of the effect of HPP on the packaging structure should
lead to improved packaging. Using unsuitable packaging structures may lead to
undesirable outcomes, including ﬂavor scalping by the package, migration of undesirable
components from the packaging material to the product, and permeation of gases and
vapors from the external environment into the package and subsequently into the product.
The exchange between the package and its environment is dependent upon the integrity
of the packaging structure and mass transfer characteristics of the packaging materials.

The mass transfer properties (sorption and permeability) of these materials should
not be affected in such a manner that they may signiﬁcantly affect product quality and
shelf life. While many researchers have dealt with the speciﬁc effects of HPP on various
food constituents, relatively few investigations have dealt with the effect of HPP on food

packaging materials. Changes resulting in plastics due to HPP are of prime importance in

food packaging applications, where such changes may directly affect the quality of
packaged foodstuff. There exists limited data on permeability, physical and mechanical
integrity, sorption and migration behavior of ﬂexible packaging structures exposed to
HPP.

These studies, therefore, focused on the permeability, mechanical properties and
integrity at microscopic level, and also the sorption behavior of selected ﬂexible
packaging structures.

The protection of packaged foods from gas and vapor exchange with the
environment depends on the integrity of packages, and on the permeability of packaging
materials. Changes in permeation, migration, sorption, and package integrity after
pressure treatment may negatively affect product safety, quality and shelf life. Sorption is
directly related to food quality and has also been considered to be a main factor in
degradation of ﬂavor or food quality (Nielsen and Giacin, 1994; Fukamachi et al, 1996).
Pressure-temperature induced changes in the materials should not signiﬁcantly affect the
barrier (permeability), mechanical, and mass transfer (sorption) properties of the
packaging structures. Knowledge of any such effects would be of importance to the food
industry and government food regulatory agencies. Present information is not sufﬁcient
for prepackaged hi gh-pressure treatment of food. Thus, the food industry must take full
responsibility for determining the suitable ﬂexible packaging structures to keep food of
good quality and safe. Quality loss may result from mass transfer. In addition to mass
transfer properties, mechanical properties and sorption behavior may play key roles in
quality loss of packaged food products. For successful development of safe and good

quality HPP food products, a better understanding of mass transfer issues within the

food/package system is important to ensure consumer conﬁdence.

Previous researchers have shown that ﬂexible packaging materials can be used in
HPP of pre-packaged food, because they were able to withstand the process without
visible signs of integrity loss (Mertens, 1993; Knorr, 1995). However, there is little
published data that reports on the effects of such treatment on the mass transfer,
mechanical and physical properties of HPP treated materials.

Based on these considerations the possible effects on the mechanical, barrier, and
sorption properties of a series of hi gh-barrier food packaging multilayer structures were
evaluated under a variety of HPP conditions. The ﬂexible plastic structures were tested
for effects of pressure, process time, and temperature on their various mechanical, barrier

(permeability) properties and sorption behavior.

The speciﬁc objectives of this research are:

a. To evaluate possible changes in the gas and vapor permeability of the package
material after high pressure treatment.

b. To evaluate mechanical behavior of selected packaging structures exposed to high
pressure treatment relative to the package material at atmospheric pressure.

c. To highlight the changes occurring at the microstructural level and visualize the
microstructure of the selected structure after the package material was exposed to
high pressure treatment

(1. To evaluate the magnitude of sorbate (d-limonene) in both the selected ﬂexible

structures and the food simulant in selected high pressure treated and untreated

ﬂexible structures.

Hypothesizes

I It is expected that high pressure will not affect the morphology of the polymer,
and thus permeability of a treated single layer plastic material will not be
affected signiﬁcantly. Permeability of a treated multilayer plastic structure, on
the contrary, may be affected since the interlayer bonding can be disrupted due
to difference in coefﬁcients of compressibility and the layer relaxation.

II The mechanical properties of a single layer plastic will not be affected Since
HPP will not affect polymer morphology. HPP may affect integrity of
multilayer structure due to different compressibilities.

III The solubility coefﬁcient of a single layer should remain unaffected by HPP
because it will not affect the morphology of the single layer polymer. On the
other hand, solubility coefﬁcient of treated multilayer plastic structures may be

affected depends on different compressibilities of multilayer structure.

The knowledge gained from this project will further the development of safe, high
quality, value-added food products to meet consumer needs and preferences, and enhance

the long term viability of food industry within the global economy.

REFERENCES

Anon A. 1996. Squeezing vacuum packed foods for freshness. Packaging Strategies. 14
(14): 5.

Barbosa-Canovas, G., Pothakamury, U.R., Palou E., and Swanson, G. B. 1998.
Nonthermal Preservation of Food. Marcel Deker.

Campbell, A.J., and Goddard, R. 1993. It is all a mater of good taste. Packaging week.
9(9): 27-28.

Cano, M. P., A. Hernandez, and B. D. E. Ancos. 1997. High pressure and temperature

effects on enzyme inactivation in strawberry and orange products. Journal of Food
Science. 62(1): 85-88.

Cheﬁel, J .C. 1992. Effects of high hydrostatic pressure on food constituents: an
overview; p. 195-209. In C. Balny, R. Hayashi, K. Heremans, and P. Masson (ed.),
High pressure and biotechnology. Colloque INSERM/John Libbery Co. Ltd.
London.

Farkas, D and Hoover, GD. 2000. Journal of Food Science sublement. High pressure
processing. 65 (4) 47-64.

Fukamachi, M., Matsui, T., Hwang, Y. H., Shimoda, M.,and Osajima, Y. 1996. Sorption
behavior of ﬂavor compounds into packaging ﬁlms from ethanol solution. J Agri.
Food Chem. 44: 2810-2813.

Hernandez, R. J. 1997. Food Packaging Materials, Barrier Properties and Selection. In:
Handbook of Food Engineering Practice, Chapter 8. Edited by K. Valentas, E.
Rolstein, and R. Singh. CRC Press, Boca Raton, Florida.

Hernandez, R. J. 1996. “Plastic in Packaging” Ch.8 in Handbook of Plastics, Elostomer,
and Composites, 3 rd ed., C.A. Harper, Ed., McGraw-Hill, New York.

Hayashi, R. 1989. Application of high pressure to food processing and preservation:
philosophy and development; p. 815-826. In E. L. Spiess and H. Schubert (ed.),
Engineering and Food. Vol (2), Elsevier London

Hoover, D. G., Metrick, C., Papineau, A. M.., Farkas, D. F and Knorr, D. 1989.
Biological effects of high hydrostatic pressure on food microorganisms. Food
Technology. 43289-107.

Kimura, K. 1992. Development of a new fruit processing method by high hydrostatic
pressure, p.279-283. In C. Balny, R. Hayashi, K. Heremans and P.Masson (ed).
High pressure and biotechnology. Colloque INSERM / John Libbery Co. Ltd.
London.

Knorr, D. 1994. The packaging applications of ultra-high pressure, ambient temperature
sterilization. IOPP packaging technology conference proceedings. November 11-12.
Chicago.

Knorr, D. 1995. Hydrostatic pressure treatment of food: equipment and processing, p.
134-159. In Gould, . W (ed.),. Ch 7. In New Methods of Food Preservation, Blackie
Academic and Professional. New York, NY.

8

Mertens, B. 1993. Developments in high pressure food processing part 1. —Internationale
Zeitschriﬁ fuer Lebensmittel Technik, Marketing, Verpackung—und-Analytik. 44(3):
1 00-104.

Mertens, B., and G. Deplace. 1993. Enginerring aspects of high pressure technology in
the food industry. Food Technology. 47(6): 164-169.

Mertens, B. and Knorr, D. 1992. Developments of nonthermal processes for food
preservation. Food technology. May. 124-1 33.

Nachmanson, J. 1995. Packaging solutions for high quality foods processed by high
icostatic pressure. Europak 95: Dusseldorf, Germany, 3-4 Oct. 1995, The 7th
International Conference on Plastics Packaging for the Food and Beverage Industry.
pp: 390-401.

Nielsen, T.J., and Giacin, J .R. 1994. The sorption of limonene/ethyl acetate binary vapor
mixtures by a biaxially oriented polypropylene ﬁlm. Packaging Technology and
Science 7:247-258.

Ohlsson, T. 1996. Minimal processing with thermal methods. International symposium
on minimal processing and ready made foods. SIK. Goteborg, Sweden.

Palou, E., Lopez, M. A., G. Barbosa-Canovas, and G. B. Swanson. 1999. High pressure
treatment in food preservation. p. 532-576. In Rahman, S. (Ed.). Handbook of
Food Preservation. Marchel Dekker, Inc, New York, NY.

Pre, G. 1992. Trends in food processing and packaging technologies. Packaging
Technology and Science. (5): 265-269.

Ting, E., Balasubramaniam, V.M., and Raghubeer, E. 2002. Determining Thermal
Effects in High- Pressure Processing. Food Technology. 31-35.

Sanchez, I.C.; Cho, J .; and Chen, W. J. 1993. Universal response of polymers, solvents
and solutions to pressure. Macromolecules. 26, 4234-4241.

CHAPTER 1
Literature Review

Consumers are demanding today higher quality food with fresh-like attributes that
provide convenience, safeties and have long shelf life.

Traditionally, thermal processing is used in the food industry to increase shelf life
and maintain food safety by subjecting the food to temperature for several minutes
(Barabosa-Canovas et al, 1998; Hayashi, 1989). This energy may result in unwanted
reactions in the food, leading to undesirable changes or formation of by-products.
Therefore, less damaging treatments with fewer additives are required to preserve food
product quality without loss of “fresh” taste. Not only shelf life demands but also food
quality requirements and sensory needs lead to a need for preserving food using
nonthermal methods (Nachmanson, 1995; Palou et al, 1999). Nonthermal methods for
food preservation are being developed to minimize the quality degradation and changes
of foods that results from thermal processing (Gould, 2000; Qin et al, 1995).

New technologies are being explored as potential alternatives to thermal methods.
New technologies include high pressure processing (HPP), oscillating magnetic ﬁelds,
high intensity pulse electric ﬁelds, and irradiation (Barabosa-Canovas et al, 1998;
Ohlsson, 1994).

Oscillating magnetic ﬁelds (OMF) is applied in the form of constant amplitude or
decaying amplitude sinusoidal waves. Preservation of foods with OMF includes package

food in a plastic bag and subjecting it to 1 to 100 pulses in an OMF with a frequency

10

between 5 to 500 kHz at temperatures in the range of 0 to 50 °C. Inhibition of growth and
reproduction of microorganism s may be explained based on breaking of covalent bonds,
cell membranes and also alteration in molecules like DNA. Frequencies higher than 500
kHz are less effective for microbial inactivation and tend to heat the food material. OMF
of frequency of 5 to 500 kHz was applied and reduced the number of microorganisms by
at least 2-log cycles (Barbosa-Canovas et all 1998; Barbosa-Canovas and Swanson 1996).

High intensity pulse electric ﬁelds (PEF) processing involves of short pulses of
high voltage (typically 20 - 80 kV/cm) to foods. In pulsed electric ﬁeld technology, the
generation of high electric ﬁeld intensities, the design of chambers that impart uniform
treatment to foods with minimum increase in temperature, and the design of electrodes
that minimize the effect of electrolysis are critical aspects. The impact of electrical ﬁelds
to biological cells in a medium causes disruption of cell membranes (Bolado-Rodriguez
et all 2000).

Irradiation is the process of exposing product to a carefully controlled amount of
ionising energy from either machine-generated electron beams or gamma rays from
cobalt-60. The ionising radiation passes through the food generating large numbers of
short-lived free radicals. These can changes to chromosomal DNA and membrane rsult in
kill micro-organisms, The length of time the food is exposed to the ionising energy and
the strength of the source determine the irradiation dose, measured in kiloGrays (kGy),

the food receives (Farkas 1997).

1.1. High Pressure Processing (HPP)

High pressure processing (HPP) refers to the application of pressure uniformly

ll

throughout a product by compressing the water surrounding the food. HPP subjects
liquid and solid foods, with or without packaging, to pressures between 300 and 800 MPa
for several minutes.

Food packages are loaded into the vessel ﬁlled with a pressure-transmitting
medium. The pressure medium, usually water mixed with a small percentage of soluble
oil for lubrication, is pumped into the vessel ﬁom the bottom. Once the desired pressure
is reached, pumping is discontinued, valves are closed, and the pressure maintained
(Deplace and Martens, 1992; Knorr, 1995). The holding time depends on the food and
processing temperature (Coles, 1997). The pressure is transmitted rapidly and unifonnly
throughout both the pressure medium and the food product (Zimmerman, 1996). A large
headspace within the package slows down the HPP and can result in a lowering of
efﬁciency of the system. Pressure is equal from all sides (Figure 1.1). Consequently the
pressure experienced by the food is independent of its volume, shape or physical state
during processing (Knorr, 1996; Mertens, 1993a). The volume decrease for water at 22°C
is approximately 4% at 100 MPa and 11.5% at 400 MPa. The whole package must be
able to return back to its original shape after pressure treatment. Pressure causes the
product to compress up to 12% depending on the pressure level (Chef’tel and Dumay,
1998). In practice, the pressure itself causes a slight rise in temperature. Adiabatic
compression of water causes a temperature increase of 2-3 °C per 100 MPa depending on
initial temperature and pressure increase, if high pressure chamber were not have
temperature controlled (Cheﬁel and Dumay, 1998; Hayashi, 1989).

This technique has unique advantages over conventional thermal treatments,

namely: it produces high quality products with minimum damage to the original

12

properties, and it can be applied at low temperatures which improves food quality
retention. Since HPP is independent of product size and geometry, its effect is uniform
and instantaneous (Mertens, 19933). Vegetative bacteria, yeast and molds in foods are
killed by HPP at 400 - 600 MPa, whereas bacterial spores require very high pressure
(Kalchayanand et al, 1998). Pressure treatment can also inactivate microbes at ambient
temperature, without the use of preservatives (Mackey et al, 1994). Since high pressure
has had promising results for its usefulness in inactivation of microorganisms and
enzymes this technology could be used by itself or in combination with other techniques
to develop shelf-stable products for consumers (Meyer et a1, 2000; Gola et al, 1996).

The possibility of increase product shelf-life without subjecting it to excessive
heat meets well with consumer demand (Swientek, 1992). HPP avoids several of the
disadvantages of thermal methods that have been used successfully to extend the shelf
life of high acid foods. There is an increasing interest in the use of HPP to extend the
shelf life of low-acid foods. HPP can be used as an alternative to thermal preservation for
the processing of food, but has not really reached the point of full commercial utilization
at this point in time (Patterson and Kilpatrick, 1998; Mermelstein, 1997, 1998).

Food can be high pressure processed in two fundamentally different ways: batch

HPP technology and semi-continuous HPP technology.

1.1.1. Batch HPP Technology
In the batch operation system, packaged food is loaded into the pressure vessel,
the vessel is closed, and water is pumped into the vessel to displace any air. When the

vessel is full, the pressure relief valve is closed, and water is pumped into the vessel until

13

the desired pressure is reached. The compression rate is proportional to the horsepower
of the pressure pump. When the process time is completed, the pressure relief valve is
opened and the water used for compression is allowed to expand and return to
atmospheric pressure. The package is then removed Figure 1.1 (Farkas and Hoover,

2000)

F: High pressure
applied

 
   
 
 

 
  

High pressure
chamber

/Food in ﬂexible

Water- oil based
liquid medium

1 2
PI, VI P2, V2

Figure 1.1 A typical schematic view of the batch high-pressure processing vessel for a
packaged food product 1) before pressure 2) during pressure.

1.1.2. Semi-Continuous HPP Technology

Semi-continuous HPP uses a pressure vessel containing a free piston to compress
liquid food. As the vessel is ﬁlled, the free piston is displaced. When ﬁlled, the inlet port
is closed and high-pressure process water is introduced behind the free piston to
compress the liquid food. After the appropriate process hold time, the system is
decompressed by releasing the pressure on the high-pressure process water. The treated
liquid is discharged from the pressure vessel to a sterile hold tank through a sterile
discharge port. The treated liquid food should be ﬁlled aseptically into a pre-sterilized
container. The process then repeats for as long as needed to meet production

requirements (F arkas and Hoover, 2000).

1.2. Critical Process Factors
To ensure that a given product is sterilized, certain variables need to be measured

(Farkas and Hoover, 2000; Meyer et al, 2000).

i type of microorganism
ii temperature, pressure magnitude, and holding time
iii ratio of pressurizing ﬂuid to product in vessel chamber

1.2.1.1 Type of Microorganism
High pressure is capable of inactivating microorganisms through the effects of
pressure do not mirror the effect of temperature. Grarn-positive bacteria are usually more

pressure resistant than gram-negative bacteria. The major cause of damage to

15

microorganisms subjected to high pressure is due to modiﬁcation of the molecules in the
cell membranes leading to increase permeability (Hoover 1993). Applied at room
temperatures, high pressure is likely to kill vegetative microorganisms although spores
present are more resistant, but when combined with mild thermal treatment they too may
be inactivated. The more developed the life form, the more sensitive it is to pressure.
Composition, pH, and water activity of the food are also key factors for HPP (Meyer et

al, 2000).

1.2.1.2 Temperature, Pressure Magnitude, and Holding Time

Increasing the pressure magnitude, time, or temperature of the pressure process
will increase the number of microorganisms inactivated. Temperatures in the range of 50
°C appear to increase the inactivation rate of food pathogens and spoilage microbes
during HPP treatment. Since products are compressed, there is the combined effect of
increasing temperature and pressure. All compressible substances change temperature
during compression. The magnitude of this change depends mainly on the compressibility

of the substance (Farkas and Hoover, 2000).

1.2.1.3 Ratio of Pressurizing Fluid to Product in Vessel Chamber
Since Speciﬁc heat of the pressurizing ﬂuid differs from that of a food product,
the ratio of the food product to pressurizing ﬂuid must be kept the same to obtain a

repeatable result (Meyer et al, 2000).

16

1.2.2.1 HPP Sterilization Production Cost:

An example of the production costs a per-pound cost is: Labor $ 0.009/1b,
maintenance $0.018/lb, depreciation $0.0185/lb. The total cost is estimated to be
0.0455/lb. A cost of about $ 0.03/lb is possible with expected future improvements

(Mayer et al, 2000). The cost of the vessel will decrease over time.

1.3. Food Packaging and High Pressure Processing

HPP is getting closer to becoming a commercial reality as a method to increase
shelf life. HPP product is available in the Japanese market, and interest is increasing in
the food industry in Europe and in the USA. In Japan, HPP is done commercially on a
meaningful scale with fruit jams, jellies, salad dressing, yogurts, ﬁ'uit mixes, ﬁ'uit juice
and concentrates. In the United States most of the activity has been still conﬁned to
research labs and pilot plants, where good results have been obtained. High pressure
processing is already being used commercially for pasteurization of few products such as
guacamole, meats, and seafood but not yet for sterilization (Meyer et al, 2000). A
combination of vacuum packaging and high pressure is now being used by food
processors. Unprocessed food in vacuum-packed containers may subjected to pressures
(Anon, 1996). Commercially, the HPP system is being used for freshly squeezed citrus
juice in ﬂexible HDPE bottles (173 MPa, 10 min). Packaging, when under pressure, must
be able to accommodate a 5-7% reduction in liquid volume (Ayshford, 1997). More
attention is also being focused on the suitability of packaging technology with this
method.

Foods can be processed in bulk followed by aseptic ﬁlling, such as individually

l7

prepackaged food in non-rigid containers. These are then sealed before being subjected
to HPP. In this case, suitable packaging materials for high-pressure treatments are
required. Packaging design and material properties are important challenges for the high
pressure processing industry. Plastic packaging materials play a signiﬁcant role in the
HPP foods in order to prevent microbial recontamination after treatment. For HPP, some
types of packaging will not stand up to the pressure without problems. Glass and metal
containers are not likely to be suitable. Paperboard cartons will also suffer some
degradation. Flexible packaging, using either laminated or monolayer ﬁlms, is the most
suitable and is widely used (Mertens, 1993b; Knorr, 1995). This is because rigid
packaging such as metal cans or glass bottles tends to fracture or become distorted. Films,
which contain metal foils or thin paper layers, may be used, but inner and outer layers
should be plastic in order to achieve a good heat seal and good protection from the
pressure medium (Mertens, 1993a; Mertens, 1993b; Nachmanson, 1995).

To ensure the development of safe and good quality food products using HPP
technology, an understanding of mass transfer issues within the food/package system is
an important safety consideration. Changes in permeability of the packaging materials, as
well as the loss or gain of speciﬁc aroma constituents during storage or distribution, can
result in product quality loss. Although packaging is a key factor to preserve food
qualities, compatibility between packaging and high pressure treatment has been largely
neglected (Mertens, 1993b).

One of the disadvantages of plastic packaging, for even high barrier materials, is
its permeability to vapors and gases that reduce the shelf life of certain foods. After high

pressure processing, the properties of these materials should not be affected in such a

18

manner that their mi gration, sorption and permeability potentials to gases and ﬂavors
may signiﬁcantly affect product shelf life and quality. While many researchers have dealt
with the speciﬁc effects of HPP on various food constituents, relatively few
investigations have dealt with the effect of HPP on food packaging materials. Changes in
plastics due to HPP are of prime importance in a food packaging application, where such
changes may directly affect the quality of a packaged foodstuff. There is not much
research reported on the effect of HPP on packaging materials for food packages. None
of the tested materials showed any signiﬁcant changes in mechanical strength even
though some showed surface deformation. Therefore, these changes seem to have small
or no effect on the shelf life of packaged foods. The magnitude of these changes depends
on the type of structures and the processing conditions. Even though some barrier
properties may be affected by HPP, the author found no evidence that these changes
have a negative impact on performance of the materials (Lambert et al, 2000).

Laminated plastic package structures were ﬁlled with water and then pressure
treated at 400MPa, for 10 min. Oxygen and water permeability properties of the ﬁhns
did not change due to HPP. An extraction test on the ﬁlms was carried out using 4%
acetic acid, 20% ethyl alcohol, and n-heptane. The amounts of evaporation residue were
at an acceptable level. Tensile strength properties of a PP/PVdC/PP structure were also
measured. Pouches were made of this ﬁlm and ﬁlled with water, sealed and pressurized at
400 MPa, for 10 min. The author reported that tensile properties did not change due to
the high pressure treatment (Ochiai and Nakagawas, 1992).

Mertens (1993 c) investigated the mechanical properties of ﬂexible packaging

ﬁlm after HPP (400 MPa and 60°C for 30 minutes). Flexible structures used in this study

19

were LLDPE/EVA, EVOH/EVA /LLDPE, and PET/Al Foil/PP. Their mechanical
properties, tensile strength, and elongation were compared with the corresponding values
for non-treated ﬁlm. Tensile strength and elongation properties of these structures were
unchanged by the high-pressure treatment.

Masuda et a1 (1992) investigated the following ﬂexible structures: PP/EVOH/PP,
OPP/EVOH/PE, PVDC-coated OP/CPP and PET/Al/CPP. They measured the water
permeability at 40 °C, 90 % and oxygen permeability at 23 °C, 90 % RH. Films were
treated at 400 MPa and 600 MPa for 10 min at 20 °C. Pressure treatment did not change
barrier properties against water and oxygen. They also measured the tensile strength and
heat seal performance of these ﬁlms. The author reported tensile and heat seal
performance were not affected by the high pressure treatment.

Little is known about sorption and migration processes from pressurized
materials. HP-treatment did not result in a signiﬁcant increase of overall migration of the
packaging materials tested (Mertens and Knorr, 1992). HPP did not affect migration from
pressurized packaging ﬁlms containing four solvents (water, 4% acetic acid, 20% ethyl-
alcol and n-heptane) (Ochiai and Nakagawas, 1992).

In another detailed study, Lambert et a1 (2000) were investigated package
properties after HPP. Pouches made of six different multilayer ﬂexible ﬁlms (15x15 cm)
were ﬁlled with 25 cl of food simulants (distilled water, 15 % ethyl alcohol, 3% acetic
acid, olive oil). Flexible structures were: 1) PA/70 um PE (medium density), 2) PA/ 60
um PE (linear), 3) PA/ 40 um PE, 4) PET/PVdC/PE, 5) PA/PE surlyn, 6) PA/PP/PE.
Pressurization processes were carried out at 200, 350, and 500 MPa for 30 min at ambient

temperature. Oxygen permeability of treated packages 2, 4 and 6 were allowed a

20

deviation of 12 %. However, the oxygen permeability of packages 1 was increased 25 %,
and package 5 was decreased 16 %. Even though these exceeded levels of oxygen
permeability, there were still within acceptable limits according to these authors.
Changes in water permeability were higher than those packages for oxygen permeability.
Values of water permeability were increased for packages 1, 4 and 6 more then a 12 %,
but water permeability were decreased for packages 2 and 5. However, according to
same authors reported that the water permeability properties of the packages stayed
acceptable and compatible for the foodstuff. Modiﬁcation in barrier properties did not
seem to be very signiﬁcant. Tensile properties of most of the plastic structures after HP
treatment were within the allowable deviation of 25%, however, PA/ 40 um PE was not
within the allowable deviation after high pressure treatment. The global migrations of
packages were also evaluated after HPP treatment (500 MPa for 30 min at 20 °C).
Selected plastic packages were in contact with four simulants for 10 days at 40 C. All the
values for global migration of the treated ﬂexible plastic were the same before and after
treatment. Global migration of the packages did not seem to be correlated with the ﬁlm
thickness, the materials nature, or the fabrication process (Lambert et al, 2000).

Few studies have been published related to the sorption process. Kubel et a1
(1996) investigated sorption of aroma compounds p-cymene and acetophenone into
ﬂexible packaging ﬁlm. The ﬂexible structures were LDPE/HDPE/LDPE, PET/LDPE,
and HDPE. Internal pouches (70x12 mm) and external pouches (105x15 mm) were
prepared. The internal pouches were ﬁlled with a solution of HzO/EtOI-I/p-cymene or
HZO/EtOH/acetophenone and then sealed. These pouches were placed into external ones

which had been ﬁlled with HzO/EtOH, then sealed. After pressure treatment in the range

21

of 0.1- 450 MPa, diffusion rates were measured as function of pressure by UV
spectroscopy. Under high hydrostatic pressure, the concentration of p-cymene and
acetophenone was not signiﬁcantly affected. Diffusion of food components into the
packaging material during exposure to high pressure did not affect the aroma of high

pressure sterilized food.

1.4. Packaging and Protection

The main purpose of packaging food is protect the packaged product from the
environmental inﬂuence from the outside inﬂuence, through processing to ﬁnal
consumption (Robertson, 1993).

Product quality, or shelf life, is determined by the following parameters: a) the
product’s physical, chemical, and biological characteristics; b) processing conditions; c)
package characteristics and effectiveness; and d) the environment to which the product is
exposed during distribution and storage (Hernandez and Giacin, 1998).

While the package serves as a barrier between the product and environment to
which the product/package system is exposed, the degree of protection varies. This
variation is particularly important in connection with the transport of gases, vapors, or
other low molecular weight compounds between the external environment and the
internal package environment. These transports are controlled by the packaging material.
The speciﬁc barrier requirement of the package system will be dependent upon the
product’s characteristics and the intended end -use application. For the purpose of
package design and optimization, it is important to consider how the mass transfer

characteristics of the packaging material determine the transport of low molecular weight

22

compounds both into and through the package (Hernandez and Giacin, 1998).

1.4.1. Plastic Structures As Food Packaging Materials

Plastic structures are polymeric materials built up from long repeating chains of
molecules and are commonly used as packaging materials for foods. These organic
(carbon-containing) molecules can be formed into a variety of products. The length of the
plastic’s molecules and the speciﬁc monomers present determine the properties of the
plastic. All plastics, whether made by addition or condensation polymerization, can be
divided into two groups: thermoplastics and thermosetting plastics. These terms refer to
the different ways these types of plastics respond to heat. Therrnoplastics can be
repeatedly softened by heating and hardened by cooling. Therrnosetting plastics, on the
other hand, harden permanently after being heated once. Almost all polymers used for
food packaging purpose are thermoplastics (Rodriguez, 1984; Paine and Paine, 1983).

Plastics are widely used in the food packaging industry because of their relatively
low weight, ability to color when manufacturing, extremely competitive cost,
transparency, barrier properties and mechanical strength, and the ability to mold complex
shapes relatively easily. Therefore, the usage of various plastics for food packaging has
been in great demand as compared with other materials such as glass, metal, and paper
(Matsui and others, 1992). Increasing use of plastics is sustained by the growth of the
food packaging industry (Gnanasekharan and F loros, 1997). However, plastics can also

interact with foodstuffs, and this interaction can affect the quality of the packaged food.

23

1.5. Mass Transport Phenomena and Food / Packaging Interactions

Interaction between food and packaging inﬂuences the overall product quality.
One of the primary functions of packaging is to protect food from contamination and to
preserve its safety and quality. Plastic structures are not absolute barriers against gases
such as oxygen. Even glass and metal containers are not completely inert with respect to
foods. However, the large increase in the use of plastics for packaging has increased the
degree to which packaging directly affects food. The shift from absolute barrier type
packages to semi-permeable polymeric packaging systems has created a need to develop
a better understanding of the transport behavior through polymer ﬁlms (Hernandez et al,
1986). This also requires better understanding of the factors that inﬂuence transport
mechanisms and food package interaction (Gavara and others, 1996). Food-packaging
interactions can be deﬁned as chemical and/or physical reactions between a food, its
package, and the environment which alter the composition, quality, or physical properties
of the food and/or package (Hotchkiss, 1995; Giacin, 1995). This is mainly associated
with the mass transport of gases, water vapor and low molecular mass organic
compounds between product, packaging material and storage environment. In food
packaging, mass transfer is often decisive factor in determining the applicability of
plastic ﬁlms as protective packaging structures (Hernandez, 1997).

Mass transfer processes in packaging systems normally encompass a number of
phenomena referred to as either permeability, sorption, and migration (Giacin and
Hernandez, 1997).

In general, food-package interactions can be divided into four types:

1. Egress permeation: Transfer of product components through the package to the

24

environment. Loss of aroma-ﬂavor volatiles, C02, or H20 can result in changes
in food quality.

2. Ingress permeation: Transfer of environmental components through the
package to the product. Ingress of 0;, H20 or undesirable odors or toxicants
can be detrimental. Packaging materials that interrupt this process (e. g., oxygen
interceptors) can be beneﬁcial.

3. Scalping, sorption: Transfer of product components to the package Transfer of
desirable aromas from food to packaging can result in ﬂavor alteration and/or
loss of package performance. Sorption of undesirable ﬂavors or reduction in 02
content of a package could be beneﬁcial.

4. Migration: Transfer of package components to the product. This can result in

safety concerns and ﬂavor degradation. Transfer of desirable ﬁmctional
components such as antimicrobial agents may be beneﬁcial (Hotchkiss, 1995;

Hernandez, 1997).

Mass transport in polymers is very complex and is discussed in the following

sections: permeability, sorption and migration.

1.5.1. Permeability

Barrier properties are very crucial parameters in selecting packaging materials for

food products. This is due to the fact that the barrier properties, including oxygen, water,

and carbon dioxide barrier is among factors controlling shelf life and the quality of many

packaged products. For each product, certain requirements must be met by the package,

but these requirements may vary widely from one product to another. Barrier properties

25

vary and are dependent on the individual polymer’s chemical and physical properties.
When a polymeric material is used to pack food, gases and water vapor may permeate
from the surrounding environment into the package. The number of gas and vapor
molecules that penetrate into a package depends on the characteristics of the polymer, the
characteristics of the penetrating molecules, their interaction, temperature, the penetrant
concentration, and the water content (Hertlein et al, 1995).

Permeability is a mass transfer process associated with a function of the partial
pressure differential of a gas or vapor between the two sides of packaging structures,
among other parameters. Permeation is the diffusional molecular exchange of gases,
vapors or liquid permeants across a plastic structure, interaction between polymer ﬁlms
and food, allowing the contents of a package to interact with the environment and vice
versa (DeLassus, 1986; Hernandez, 1996). Permeability is referred to as the product of
the thermodynamic parameter of solubility and the kinetic parameter of difﬁrsion. The
diffusion coefﬁcient describes how quickly the molecular species moves in the ﬁlm and
the solubility coefﬁcient is a measure of the quantity of a substance that will be sorbed by
the polymer. The rate of permeability is greatly inﬂuenced by the absorption and
solubility of the molecules in the polymer (Hernandez, 1996; Giacin and Hernandez,
1997). The deterioration of packaged foodstuffs largely depends on transfers that may
occur between the internal environment and the external environment (Giacin and
Hernandez, 1997). The mechanism of permeation of gases and vapors though polymers
can be summarized: a) Absorption and solution of penetrant at one surface of the
polymer; b) Diffusion of the penetrant through the polymer matrix; c) Desorption of the

penetrant from the other surface of the polymer (Rogers, 1985; Hernandez, 1997,

26

DeLassus 1986).

The diffusion ﬂow (F) of a permeant through a polymer ﬁlm is related to the
amount of permeant passing through a surface of unit area normal to the direction of ﬂow
during unit time, as described by the following equation:

F=Q/A t (1)
where F diffusion ﬂow or ﬂux, Q is the amount of permeant, A is area, and t is time.
If the permeation rate and the concentration gradient is one of direct proportionality,
Fick’s ﬁst law of diffusion applies (Mohney et al, 1998; Hernandez, 1997).

ac
F _ ma _ (2)

where F is the ﬂux (rate of the transport) per unit area of permeant through the
polymer, c is the permeant concentration in the polymer, and D is the diffusion
coefﬁcient. Therefore, 8c/ ﬁx is the concentration gradient of the permeant across a
thickness x.

Permeation is described by the permeability coefﬁcient (P), diffusion coefﬁcient
(D) and solubility coefﬁcient (S):

P=D S (3)

The solubility coefﬁcient is a measurement of the concentration of penetrant
molecules sorbed in the polymer matrix. In an unsteady state ﬂow case, from a mass
balance standpoint, assuming that diffusion takes place only in the x direction, Fick’s

Second Law provides the relationship:

27

 

(4)

where t is time.

When a polymer is contacted on both sides with a penetrant at different
concentration values, this expression can be integrated at the surface x=0, the penetrant

concentration c=c2 and at x=L, c=c2; yielding equation (5).

_ D(cl —c,)

F L (5)
At sufﬁciently low concentrations, Henry’s law often applies and the above
expression can be rewritten by substituting for c.
c=S p (6)
F=DS=——(p2-p‘) (7)
L
Where D S is referred to as the permeability coefﬁcient or constant and is
represented by the symbol P. Converting the ﬂow rate to a ﬂow per unit area, F=q/At,
combining the equation above, and rearranging equations yields equation (8):
P = DS - 3L— (8 )

_ AtAp
where the permeability coefﬁcient or constant, P, equals the amount of permeant
(1 (00, g) that has passed through a material of known thickness L (m, cm, mil) per unit
area A (m2 ,100 in2 ), in a given time t (sec, hr, day), at a known partial pressure
difference Ap (atrn, Pa, mmHg).

The transmission rate refers to the quantity of permeant derived from the

28

expression for permeability disregarding thickness and the partial pressure gradient of the
permeant (Robertson, 1993).

The permeability through a barrier polymer is dependent on several internal and
external factors. The internal factors include the chemical structure of the polymer and
permeant, and the physical structure of polymer (Koros et al, 1988; Nemphos et al, 1986).
The external factors include the nature of the permeant, and the environmental conditions
such as temperature and relative humidity. Each variable must be known, speciﬁed and
controlled in order to obtain reliable, repeatable test results.

Many experimental techniques have been employed for measuring permeability

and can be categorized as follows (Gavara and Hernandez, 1999):

i Pressure variable methods
ii Isostatic method
iii Quasi-isostatic method

1.5.1.1. Pressure Variable Methods

The ASTM standard method D-1434 was adopted for measuring gas transmission
rates and permeabilities of ﬁlm. In this technique, the high-pressure chamber is ﬁlled
with the permeant at relatively high pressure and the permeated gas diffused to the other
side of the ﬁlm. The permeant is collected in a constant-volume chamber (pressure -
variable) or allowed to expand against a constant atmospheric pressure (volume-
variable). In the pressure variable, the cell is totally evacuated. During the diffusion
process, the pressure increase in the low -pressure chamber is measured by a pressure

gauge as a function of time (Gavara and Hernandez, 1999; Robertson, 1993).

29

1.5.1.2. Isostatic Method:

In this procedure, the ﬂow system is designed to maintain the total pressure on both
sides of the polymer at atmospheric pressure. A constant permeant vapor pressure is
continuously ﬂowed through the high concentration cell chamber, while the permeated
vapor is conveyed by N 2 to the detector. The transmission rate is measured continuously
until a steady-state value is reached (Hernandez et al, 1986; Gavara and Hernandez,
1999)

The permeability coefﬁcient can be calculated by Eq (9):

FSS L

p:
(Ap

) (9)

Where F5., is the steady state ﬂow, and the diffusion coefﬁcient D by Eq (10):

2
D = ___I;_ (10)
7.199.t0_5
where t1/2 is the time required for Ft/Fss to reach a value of 0.5.
At steady-state, the permeability coefﬁcient can be determined using following

equation (11) (Hernandez et al, 1986; Gavara and Hernandez ,1999).

_axGxL
Axb

P (11)

where: a is the calibration factor to convert detector response to unit of mass of permeant
((mass/volume)/signal unit), G is the response unit from the detector output at steady
state (signal output), f is the ﬂow rate of sweep gas conveying penetrant to detector
(volume/time), A is the area to the penetrant (area unit), L is the ﬁlm thickness, b is the

driving force (the concentration or partial pressure gradient).

30

1.5.1.3. Quasi-Isostatic method
In the quasi-isostatic (pressure increase or accumulation) method, a test ﬁlm
separates two chambers where one side of the ﬁlm is exposed to the test gas, and the
other is in contact with an inert gas. Samples of penetrated permeant are withdrawn from
the low concentration cell chamber. By plotting the total quantity of permeated vapor as
a function of time, the diffusivity and permeability coefﬁcients can be determined.

Diffusivitys is calculated by:

L2

D—
6T

(12)

where L is the thickness, and T is the lag time (Pain and Pain, 1983).

The steady state permeability coefﬁcient is obtained using equation (13).

yL
P = — 13

Ab ( )
where: y is the slope of the steady state portion of the transmission rate proﬁle curve; 1 is

the ﬁlm thickness; A is the area of the ﬁlm exposed to the permeant, b is the driving force

(the partial pressure gradient).

1.5.1.4. Water Vapor Transmission Rate Measurement

The water vapor transmission rate (WVTR) is deﬁned as the rate of water vapor
ﬂow under steady state conditions through a unit area of a test ﬁlm material.

The most commonly used method for determining water vapor permeability

(WVP) is the standard test method for WVTR of materials (ASTM, 1990). This

31

gravimetric method involves sealng a test ﬁlm in a cup partially ﬁlled with water leaving
an air gap beneath the ﬁlm (Anker, 1996).

The Permatran - W 3/31 (Modem Controls, Inc. Mocon, Minneopolis, MN) is an
instrument used for measuring the rate at which water vapor diffuses through a permeable
barrier according to ASTM F1249. Test cells consist of two sections separated by the
material being tested. The RH in the enclosed chamber reaches 100%. Water vapor
permeating across the ﬁlm is transported by the dry nitrogen gas to a pressure modulated
infrared detection system which determines the moisture in dry purge air. The infrared
photodetector produces low-level electrical signals in response to the change in
transmitted infrared radiation. This signal is directly proportional to the WVTR of the

test cell.

1.5.1.5. Oxygen Tansmission Rate Measurement

The oxygen transmission rate is deﬁned as the rate of oxygen ﬂow, normal to the
two ﬁlm surfaces, under steady state conditions through a unit area of a test ﬁlm.

An instrument widely used for the measurement of oxygen permeability by this
method is the Mocon OxTran (Modem Controls, Inc, Minneapolis, Minn). The OxTran
consists of two chambers of measuring cells between which the test ﬁlm is placed. A gas
stream of known oxygen partial pressure ﬂows through one of the chambers. Oxygen -
free carrier gas is passed through the other chamber to a coulometric detector. A
computer will perform the testing procedure and display the resultant transmission rate
values for each specimen tested. This oxygen permeability tester operates according to

ASTM Standard Method D 3985-81 (Anonymous, 1981).

32

1.5.1.6. Carbon Dioxide Transmission Rate Measurement

The Permatran C-IV measures the carbon dioxide transmission rate of ﬁlm. Test
ﬁlm is clamped between the upper and lower half of the diffusion cell, then the upper half
is ﬂushed continuously with carbon dioxide gas. Perrneated gas is carried to an infrared
sensor by nitrogen gas where a response is generated proportional to the amount of
carbon dioxide present (Moco’n, 1983). The Permatran C-IV can vary in operation

according to suit the barrier properties of the ﬁlm.

Static Accumulation- This method is for testing transmission rates less than 50 cc / (m2
d). Carbon dioxide permeated through the test ﬁlm accumulates in a cell for a
predetermined time (2-80 h). The amount of accumulated carbon dioxide is quantiﬁed
using a sensor and compared with the signal produced when a known amount of carbon

dioxide is injected into an identical volume.

Dynamic Accumulation- This method is used for testing transmission rates between 50
and 300 cc / (m2 (1). As carbon dioxide permeation through the ﬁlm increases, the
corresponding output voltage increases with time, producing a straight line until its slope
is constant. The observed response is subsequently translated to carbon dioxide
concentration by comparision with the signal produced when a known amount of carbon

dioxide is injected into an identical volume.

Continous Flow- This method is used for testing high transmission rates greater than 300

cc / m2 (1. Unlike static and dynamic accumulation, continous ﬂow is operated in an open

33

loop. The carbon dioxide transmitted through the test ﬁlm mixes with the nitrogen carrier
gas, passes into the infrared sensor, and is exhausted. The test ﬁlm is compared to a
reference ﬁlm of known transmission rate which is similar to the expected value of the

test ﬁlm.

1.5.2. Sorption

Sorption behavior results in dissolution or transfer of a substance from the food to
the polymeric structure. Sorption is a process that results when a ﬂavor component of a
product is soluble in a packaging material. The volatile component dissolves into the
polymer, leaving a lower concentration in the package headspace. An imbalance in the
ﬂavor proﬁle results in a detectable reduction in the organoleptic quality of the product.
As opposed to plastic structure’s prevalence, a serious problem has been identiﬁed
concerning deterioration of intrinsic food ﬂavors by plastic ﬁlms (Matsui et al, 1992,
Moshonas and Shaw, 1989). This sorption behavior depends on the relative strengths of
the interactions between the permeant molecules and the polymer. In food product-
package systems, sorption behavior needs to be characterized for quality control and for
predicting the change in product quality, as related to the loss of components associated
with product shelf life (Hernandez and Giacin, 1998). Consumer rejection of food is
commonly associated with the presence of unacceptable ﬂavors. In general, packaging
materials can alter the ﬂavor proﬁle of packaged foods by absorbing ﬂavor components,
chemically reacting with food components to produce off-ﬂavors, and/or by releasing
components that produce off-ﬂavors into the food (Gnanasekharan and Flores, 1997;

Mannheim et al, 1987). This phenomenon may be brought about by the sorption of

34

ﬂavors in the plastic layer because the ﬁlm is in direct contact with foodstuffs over time
(Matsui and others, 1992). The solubility of essential ﬂavor in the polymer structure is of
paramount importance in avoiding the effect of “ﬂavor scalping” or loss due to sorption
(Fayoux et al, 1997). In a food packaging structure, the package material should sorb a
minimum amount of the critical food-ﬂavorants. The amount of sorption is expressed by
the solubility coefﬁcient, which describes how many molecules are in the polymer
matrix. Several models have been proposed to describe sorption behavior, the main
models are Henry’s, Langmuir, and F lory-Huggins types (Rogers, 1985; Hernandez,

1996; Stern and Trohalaki, 1990).

1.5.2.1. Henry’s law sorption

Henry’s law sorption is the simplest case of sorption, which applies to an ideal
case and occurs when interactions between the polymer/permeant and permeant/permeant
are weak compared with the stronger interaction between the polymer/polymer
interaction. In this case, the solubility coefﬁcient is independent of the sorbed permeant
concentration and the sorption isotherm shows a linear relationship between sorbate

amount and permeant pressure at a given temperature (Rogers, 1985).

1.5.2.2. Langmuir sorption isotherm

This type of sorption is characterized by a high level of sorption occurring at a
relatively low pressure. This is a characteristic of initial sorption on speciﬁc sites or
microvoids in the polymer structure. After saturation of the active site, the permeant

starts to dissolve in to the polymer matrix (Hemandez, 1996). A region of higher

35

concentration may try to overtake a region of lower concentration (Sheng and Smith,

1 999).

1.5.2.3. Flory-Huggins sorption
This type of sorption is where the penetrant/penetrant forces are stronger then the
polymer/permeant interactions. The solubility coefﬁcient increases with vapor pressure

(Fayoux et al, 1997; Rogers, 1985).

1.5.2.4. Dual-mode sorption

This type of sorption is based on the existence of two sorbed penetrant
populations in the polymer. One population of the permeant molecules dissolves into the
polymer by a mode which obeys Henry’s law, while the other population is sorbed into
voids of the polymer obeying Langmuir type sorption (Stern and Trohalaki, 1990). The
resulting sorption is then due to a combination of Henry and Langmuir sorption.

For a low partial pressure of gases, or for dilute concentrations of organic vapors,
the solubility follows Henry’s law:

C=S p (14)

Where C is the concentration of sorbate in the polymer, S is the solubility
coefﬁcient, and p is the vapor pressure of sorbate.

The type functional group is characteristic of the penetrant molecule and is of
great importance in determining the extent of sorption by the packaging material.

An increase in the temperature directly affects the solubility and can be described

by an Arrhenius equation (Gnanasekharan and Floros, 1997).

36

1.5.3. Migration

Migration is the transport of compounds from the packaging materials into a food
product. These compounds include residual monomers or oligomers ﬁom the incomplete
polymerization process, additives such as heat and light stabilizers, antioxidants,
antistatic agents, stabilizers, and lubricants. Under certain conditions, these relatively
low molecular weight compounds will migrate from the package to the food (Lox and
Pascat, 1996).

The migration from polymeric packaging materials to food products can be
viewed as a two-step process in which the migrants diffuse from the surface to the
contact phase, and then dissolve in the food and are dispersed therein. The desorption of a
migrant from a polymer can be considered a function of the polymer-migrant interaction
afﬁnity and diffusion. The afﬁnity is determined by the equlibrium amount of migrant
transferred to the food phase (Gnanasekharan and Flores, 1997).

The amount of contaminant migrating from a plastic ﬁlm or sheet into a food
contact phase can be adequately characterized by equations that are derived from Fick’s
ﬁrst and second laws of diffusion (Lox and Pascat, 1996).

Fick’s second law is related to non-steady state diffusion, where concentration of

the diffusing substance is changing with time (15):

dcp 02C,
—dt—=Dp( dxz ) (15)

 

‘6 99

where the subscript p indicates that parameters pertain to the polymer.
The boundary condition that describes the concentration at the interface between

the polymer and the external phase is strongly inﬂuenced by the extent of agitation,

37

composition, and the volume of the external phase. If the external phase is stagnant, the
migrant that leaves the polymer must diffuse through the external phase. Thus, an

expression similar to that in the above equation can be written (16):

2
dc: ___ Dc (1%.
dt dx

 

) (16)

Where the subscript “e” refers to the external phase. The boundary condition at
the interface with the polymer is then given and also quantitatively described by the
partition coefﬁcient (K) (Little, 1983):

2 Ce
K (C ) (17)

p

 

The transport of a migrant is dependent on the nature of the polymer matrix, the
chemical structure of both the contaminants and the food type, and the test condition

(temperature and storage time) (Little, 1983).

1.6. Factors Affecting Permeation, Sorption, and Migration Processes in Package-

Product Systems:

The mass transfer process provides the basis for further physicochemical activities
within the package system. Such activities may induce physicochemical changes in the

product (Giacin, 1995).

Sorption, or the uptake of volatile components by the polymeric packaging
material from the food, may also result in increased permeability to other permeants,
lower chemical and mechanical resistance of the packaging material, and may affect the

kinetics of the migration process. The overall effect may result in the loss of aroma and

38

ﬂavor volatiles associated with product quality, as well as other volatile organic food

components during package storage.

The permeation, sorption and migration processes are affected several factors.
The variables affecting permeation, sorption and migration can be grouped as
composition and environmental and geometrical variables (Giacin 1995, Giacin and

Hernandez 1997, Hernandez and Giacin 1998):
Composition variables
i Nature of polymer

ii Nature of permeant

Environmental and geometric variables
i Temperature
ii Relative humidity

iii Packaging geometry

1.6.1. Composition variables
1.6.1.1. Nature of Polymer

The relationship between penetrant transfer characteristics and the basic
molecular structure and chemical composition of a polymer is rather complex, and a
number of factors contribute to the sorption and diffusion processess including structural

regularity, conformational ﬂexibility and intermolecular forces of attraction (Giacin,

39

1995).

Morphology in polymer refers to the physical state by which amorphous and
semicrystalline regions coexist. It depends not only on its stereochemistry but also on

whether the polymer has been oriented or not.

Crystalline polymers have high melting points, high density. Mass transfer is
restricted to the amorphous regions of the polymer Increasing polymer crystallinity on the
reduction in sorption, diffusion and permeability properties. (Rogers, 1985; Hernandez
and Giacin, 1998). Crosslinking polymer chain restricts chain mobility and consequently
reduces permeability. Functional and side groups have effect oxygen permeability

properties such as benzene rings offer poor barrier to hydroxyl groups

Polymer free volume is also a function of structural regularity, orientation and
cohesive energy density (Giacin, 1995; Hernandez and Giacin, 1998; Rogers, 1985). The
solubility of vapors and gases in polymers is also strongly dependent on crystallinity,
since solubility is usually conﬁned to the amorphous regions (Giacin, 1995; Giacin and

Hernandez, 1997).

1.6.1.2. Nature of Permeant

The molecular structure of the permeant can play an important part. Since larger
molecules has higher cohesive force to substrate surface, increase in permeant size
mostly lead to an increase in solubility coefﬁcient values. But the decrease diffusion
coefﬁcient values. The observed concentration of the permeance values may be attributed

to penetrant/polymer interaction (Giacin, 1995).

40

Organic vapors are capable of exhibiting concentration-dependent mass transport
processes. The permeation of more condensable vapors through a polymer proceeds at
greater rates than permeation of gases. Therefore, the type and/or mixture of organic
vapors will determine the magnitude of sorption and permeation, as well as the effect of a

co-permeant on penetrant permeability.

The polymer and the permeant have similar chemical composition or polarity,
high permeability is expected. Polar compounds will tend to dissolve in polar solevent

(Giacin, 1995; Hernandez and Giacin, 1998).

1.6.2. Environmental and geometric factors
1.6.2.1. Temperature

Permeability (P), diffusion (D), and solubility (S) coefﬁcients are affected by

temperature following the Arrhenius relationship. as given in the following equations:

 

 

 

—E
D=D ex D
0 P( RT)

AH

S=S ex 5
o p(RT)

P=P ex _ p
0 p(RT)

where D, S, P are coefﬁcients; Do, So, and P0 are pre-exponential constants, Ed is
the activation energy for diffusion, AHs is the heat of solution, Ep is the activation energy

for permeation, T is the absolute temperature, and R is the universal gas constant.

41

The above equations can be used to calculate the permeability coefﬁcient at a
desired temperature from a known value. However, the permeation behavior is generally
quite different below and above the glass transition temperature (T8). Above the T8 of the
polymer, enough energy is provided to produce segmental mobility in polymer chains,
which corresponds with an increase in permeability and diffusion. Below the T3, the
polymer chains are ﬁxed in a speciﬁc conformation. In general, at temperatures above T3,
the permeability coefﬁcient is more temperature dependent (Hernandez, 1996; Hernandez

and Giacin, 1998; Frisch, 1980).

1.6.2.2. Relative Humidity

Barrier properties are mostly sensitive to the amount of moisture present in a
polymer. If water swells or plasticizers the polymer chains, the gas permeation can
increase. This effect is due to the greater ease of polymer chain segmental mobility
(Crank and Park, 1968; Axelson—Larsson, 1992), which results in an increased gas

diffusion rate and greater sorption capacity of the polymer matrix (Lim et al, 1998).

1.6.2.3. Package Geometry

The area of exposure and thickness, shapes, the total volume are critical (Brown,
1992). The volume or mass ratio of the food phase and packaging material is also
required for quantiﬁcation of the equilibrium concentration for a speciﬁc

product/package/sorbate system (Giacin, 1995).

42

1.7.1. Mechanical Properties

Polymers are increasingly used for packaging application because of their unique
properties. In many applications, the mechanical properties of the polymer are of prime
importance. It is essential that the plastic structure retain its mechanical strength,
stability, and integrity in order for it to continue to execute its function over a useful time
without failure. Quantitative information on the mechanical parameters of ﬁlms is also
essential for designing packaging sytems. By understanding the mechanical behavior and
the factors controling it, polymeric materials can be properly and efﬁciently utilized. The

mechanical properties of the polymer are dependent on internal and external factors.

1.7.1. Effect of External and Internal Factors on Mechanical Properties

The external variables refer to factors that have an appreciable effect on mechanical
properties but are not directly concerned with the structure and composition of the
polymer. The main external factors are time, temperature, and pressure (Lawrence, 1994).
When the ambient temperature increases in a material, there is a gradual expansion of the
material, resulting in more free volume and weakening of the bonding forces that hold the
material together. In polymers, this mainly results in a reduction in the van der Waals
forces between molecules. As such, all materials have less internal strength with
increasing temperature, which is reﬂected in reduced maximum strength. Elongation at
break usually increases. As pressure is increased, the strength of the polymer invariably
increases. This would be expected since increasing pressure decreases free volume and
increases the strength of the van der Waals bonds along with the density of the material

(Lawrence, 1994, Bucknall et al, 1972).

43

The internal factors, on the other hand, are those that produce changes in
mechanical properties by directly producing changes in morphological, chemical and
physical structures of the polymer. The main internal factors are the following (Rubin
1982; Paul and Bucknall, 1999):

i chemical structure and composition,

ii degree of crystallinity

iii molecular weight

iv the presence of low molecular weight diluent (plasticizer, ﬁller etc)

v orientation and other consequences of the processing history (thermal).

Thermal properties are also important factors in determining the brittleness and the
ductility of a polymer. Tg relates to segmental mobility of the molecular chains, and it
also determines whether chain-straightening and/or molecular slippage will occur. The
chain-straightening refers to the elongation of the molecular chain from the equilibrium
position to the new dimension under stress, while molecular slippage refers to the
molecular movement past adjacent molecules due to the application of stress (Paul and
Bucknall, 1999). As polymers are placed under stress, they may exhibit both phenomena,
depending on their morphological structure. Besides the effect of thermal expansion,
increase in temperature brings about changes in the state of the amorphous polymer. At
a temperature below Tg, those phenomena do not occur appreciably. Therefore, the
polymers are hard. At a temperature above Tg, polymers exhibit chain-straightening and
molecular slippage. Therefore, the polymers are soft and ﬂexible. In conjunction with

these changes of state are changes in the mechanical behavior of the polymer (Rubin,

44

1982; Brucknall et al, 1972).

1.7.2. Tensile Properties

One of the most informative mechanical tests for any material is the determination
of its stress-strain curve in tension. The stress-strain curve for plastic serves to deﬁne
several useful quantities, including strength, yield strength, elongation at break, and
modulus of elasticity. Different materials exhibit different tensile properties. The
mechanical properties are measured by deformation of a sample and monitoring the stress
and deformation until it breaks (Anker, 1996).

Stress (c) and strain (7) are calculated from the recorded force F and deformation.
0' = F/ A
8 = L/LO

Where, A is original crossectional area, L0 original length and L the length change

during extension.

A typical shape of the stress-strain curve for plastic material is shown in Figure
1.2. A great deal of information about a material can be obtained from the shape of its
stress/strain curve (Figure 1.2 and Figure 1.3). That plot of stress versus strain can give us
another very valuable piece of information including tensile strength, yield strength,

percent elongation, modulus of elasticity, and toughness.

1.7.2.1. Tensile Strength

45

Tensile strength at break is the maximum stress that a polymer can withstand prior
to failure, divided by the original cross-sectional area supporting the load. The static
weighing test according to ASTM method D-882 is used to determine this property. The
applied force and amount of grip separation are measured. The stress and strain of the
sample are measured continuously and recorded on a chart. For determination of tensile

strength, the stress is plotted against the strain; the load against the elongation.

1.7.2.2. Yield Strength
The yield strength is the tensile stress at which the material exhibits a ﬁrst Sign of
non-elastic deformation occurs To determine this parameter the load at this point (yield

point) divided by the original cross sectional area of the specimen.

1.7.2.3. Percent Elongation

The percent elongation is the extent to which a material can extend during tension
testing and is usually taken at the point of break. Elongation is expressed as the change in
length to initial length. Deformation is simply a change in shape that anything undergoes
under stress. Usually percent elongation, which is just the length the polymer sample is
after it is stretched (L), divided by the original length of the sample (Lo), and then
multiplied by 100 according to ASTM D882:

% elongation = A L / LO

It is used as a measure of the ﬁlm’s ability to stretch, which indicates that the

material may absorb a large amount of energy before breaking (Roberson, 1993).

46

1.7.2.4. Modulus of Elasticity

Modulus of elasticity is measured by calculating stress and dividing by elongation
and would be measured in units of stress divided by units of elongation. It is a measure
of the force that is required to deform the ﬁhn by a given amount and so it is also a

measure of intrinsic stiffness of the ﬁlm.

1.7.2.5. Toughness

Toughness is really a measure of the energy a sample can absorb before it breaks.

 

tensile stress- strain
modulus curve
: I
stress tensile
strength
5 1

 

 

 

strain (elongation)

Figure l. 2. A typical stress/strain curve for thermoplastic polymers.

strong, not tough

strong and tough

stress

 

not strong, not tough

 

—"'.
strarn

Figure 1.3. Typical stress/strain curves may obtain with plastic polymers.

47

1.8. REFERENCES

Anker, M. 1996. Edible and biodegradable ﬁlms and coatings for food packaging
literature review. Ski-Report. No:623:Goteberg, SWEDEN.

Anon, A. 1996. Squeezing vacuum packed foods for freshness. Packaging Strategies. 14
(14): 5.

ASTM. 1981. ASTM D 3985-81. Standard test method for oxygen gas transmission rate
through plastic ﬁlm and sheeting using a coulometric sensor.

ASTM. ASTM D 882. Standard Test Method for Tensile Properties of Thin Plastic
Sheeting"
ASTM. 1990. ASTM F 1249-90. Standard test method for water vapor transmission rate
through plastic ﬁlm and sheeting using a modulated infrared sensor.

Axelson-Larsson, L., 1992. Oxygen permeabilities at high temperatures and relative
humidities. Packaging. Technology and Sci. 5. 297-306.

Ayshford, H. 1997. Preservation for the masses. Packaging Week vol 13 (9): 32-34.

Barbosa-Canovas, G., Pothakamury, U.R., Palou, E., Swanson, GB. 1998. Nonthermal
Preservation of Food. Marcel Deker.

Bolado-Crodriguez, S, Gongora-Nieto, M.M., Barbosa-Canovas G, and Swanson, G. B.
2000. A review of nonthermal technologies; p. 227-266. In Lozano, J.E., Anon, C,
Parada-Arias E, and Barbosa-Canovas, G (ed), Trends in Food Engineering.
Technomic Publising Co., .Lancaster. Basel.

Brown, W. E. 1992. Barrier Design. Ch 8. In Plastic in Food Packaging: Properties,
design, and fabrication. Marcel dekker. New York.

Bucknall, C.B, Gotham, K.V. and Vincent, PI. 1972. Fracture II-The empirical approach;
p. 622-653.in A. D. Jenkins (ed), Polymer science. American Elsevier Publishing
Co. Inc. New York.

Cheftel, J. C, and Dumay, E. 1998. Effects of high pressure on food biopolymer with
special reference to B-lactoglobulin. p. 370-397 in Reid. D. (ed.). The Properties of
Water in Foods ISOPOW 6. Blackie Academic and Professional.

Coles, R. 1997. Juice comes under pressure. Packaging Week. 12 (35): 22.
Crank, J. and Park, 6.8. 1968. Diffusion in Polymers, Academic Press, N. Y.

DeLassus, PT. 1986. Transport of unusual molecules in polymer ﬁlms. Tappi Journal 69
(.12)-

Deplace, G. and Martens, B. 1992. The commercial application of high pressure
technology in the food industry; p. 469-481 .In C. Balny, R. Hayashi, K. Heremans
and P.Masson (ed), High pressure and biotechnology. Colloque INSERM / John
Libbery Co. Ltd. London.

Farkas, D. and Hoover, G. D. 2000. J .Food Sci. High pressure processing. 65(4).47-64.

48

Farkas, J. 1997. Physical methods of food preservation. Food Microbiology.
Fundamentals and Frontiers. M.P. Doyle, L.R. Beauchat, T.J. Montville (eds.).
Washington, DC. ASM Press. 497-519.

F ayoux, C.S, Seuvre, AM, and Voilley, J. 1997. Aroma transfers in and through plastic
packaging: Orange juice and d-limonene. A Review. Part 2: Overall sorption

mechanisms and parameters-a literature survey. Packaging Technology and Sci.
1 0: 145- 1 60.

Frisch, H. L. 1980. Sorption and Transport in glassy polymers-a review. Polymer. Eng.
and Sci., 20. 2-13.

Gavara, R. and Hernandez, R. J. 1999. Plastics Packaging: Methods to Evaluate Food
Packaging Interactions. Pira International Review, Pira, Leatherhead, Surrey,
United Kingdom.

Gavara, R., Hernandez, R. J. and Giacin, J. 1996. Methods to determine partition

coefﬁcient of organic compounds in water/polystyrene systems. J. Food Sci.
61:947-952.

Giacin, J. R. 1995. Factors Affecting Permeation, Sorption and Migration Processes in
Package-Product Systems in Foods and Packaging Materials — Chemical
Interactions Edited by Paul Ackerrnann. Edited by Margaretha J agerstad, Thomas
Ohlsson. Cambridge.

Giacin, J. R. and Hernandez, R. J. 1997. Permeability of Aromas and Solvents in
Packaging Materials. In: The Wiley Encyclopedia of Packaging Technology, pp
724-733. A. Brody and K. Marsh (Ed), John Wiley & Sons Inc., New York, NY.

Gnanasekharan, V. and Floros, J. D. 1997. Migration and sorption phenomena in
packaged foods. Critical Reviews in Food Science and Nutrition. 37(6) 519-559.

Gola, S., Foman, C., Carpi, G., Maggi, A., Cassara, A., and Rovere, P. 1996. Inactivation
of bacterial spores in phosphate buffer and in vegetable cream treated with high
pressures. In “High Pressure Bioscience and Biotechnology” ed. Rhayashi and C,
Balny. pp: 253-260. Elsevier Science, Kyoto, Japan.

Gould, G. W. 2000. Emerging technologies in food preservation and processing in the
last 40 years. p: 1-11.in G. Barbosa-Canovas and G. W. Gould (ed.), Innovations
in Food Processing. Tecchnomic Pub. Lanscaster, Basel.

Hayashi, R. 1989. Application of high pressure to food processing and preservation:
philosophy and development; p. 815-826. In E. L. Spiess and H. Schubert (ed.),
Engineering and Food. Vol (2), Elsevier London.

Hernandez, R. J., Giacin, J .R., and Baner, AL, 1986. The evaluation of the aroma barrier
properties of polymer ﬁlm. J. Plastic Film and Sheeting. 2: 187-211.

Hernandez, R. J. 1996. “Plastic in Packaging” Ch.8 in Handbook of Plastics, elostomer,
and composites, 3rd ed., C.A. Harper, ed., McGraw-Hill, New York.

Hernandez, R. J. 1997. Food Packaging Materials, Barrier Properties and Selection. In:
Handbook of Food Engineering Practice, Chapter 8. Edited by K. Valentas, E.

49

Rolstein, and R. Singh. CRC Press, Boca Raton, Florida.

Hernandez, RI. and Giacin, JR. 1998. Factors Affecting Permeation, Sorption, and
Migration Processes in Package-Product Systems. In: Quality Preservation in
Food Storage and Distribution, Chapter 10. Edited by T. Taub and R. Singh. CRC
Press, Boca Raton, Florida, 1998.

Hernandez, R. J. and Gavara, R. 1999. Plastic packaging: methods for studying mass
transfer interactions. Pira International, Leatherhead, United Kingdom. p.5-31.

Hertlein, J .; Singh, R.P., Weisser, H. 1995. Prediction of oxygen transport parameters of
plastic packaging materials from transient state measurements. J. Food.Eng.24 (4):
543-560.

Hoover, D. G. 1993. Pressure effects on biological systems. Food Technology, 47, 150-
1 55.

Hotchkiss, J.H. 1995. Overview on Chemical Interactions between Food and Packaging
Materials in Foods and Packaging Materials — Chemical Interactions Edited by
Paul Ackermann. Edited by Margaretha J agerstad, Thomas Ohlsson. Cambridge.

Kalchayanand, N., Sikes, A. Dunne, C. P., and Ray, B. 1998. Interaction of hydrostatic
pressure, time and temperature of pressurization and pediocin AcH on inactivation
of foodbome bacteria. J. Food Protection. 61(4): 425-431.

Knorr, D. 1996. Advantages, opportunities and challenges of high hydrostatic pressure
application to food systems. P 279-287. In R. Hayashi, C. Balny (ed), High
Pressure and Biotechnology. Elsevier Science B.V.

Knorr, D. 1995. Hydrostatic pressure treatment of food: equipment and processing, p.
134-159. In Gould, G. W (ed.),. Ch 7. In New Methods of Food Preservation,
Blackie Academic and Professional. New York, NY.

Koros, W.J., and Hellums, M.W. 1988. Transport properties in encyclopedia of polymer
science and engineering. 2nd edition. John wiley and sons inc., New York.
Supplement volume. P 788-799.

Kubel, J., Ludwig, H. Marx, H., and Tauscher, B. 1996. Diffusion of aroma compounds
into packaging ﬁlms under high pressure. Packaging Technology and Sci. 9: 143-
152.

Lawrence, E. 1994. Mechanical properties of polymers and composites. M. Dekker.New
York.

Lambert, Y., Demazeau, G.. Largeteau, S, Bouvier, J.M. Laborde-Croubit, S. and
Cabannes, M. 2000. Packaging for hi gh-pressure treatments in food industry.
Packaging Technology and Sci. Vol. 13:63-71.

Lim, L. Britt, I.J., and Tung, M. A. 1998. Sorption and permeation of allyl isothiocyanate
vapor in nylon 6,6 ﬁlm as affected by relative humidity. J. Plastic Film and
Sheeting. 14:207-225.

Little, A. D. 1983. A study of indirect food additive migration. Final summary report for
FDA, HFA-Sl 1. Project number 81166.

50

Lox, L and Pascat, B. 1995. Transfer between the food product and the packaging:
migration, p 59-75. In Bureau, G. and Multon, J .L. (ed), Food packaging
technology. Volume 1. VCH Publishers, New York. NY.

Mackey, B. M.,. Forestiere, K., Isaacs, N. S., Stenning, R. and Brooker, B. 1994 The
effect of high hydrostatic pressure on Salmonella thompson and Listeria

monocytogenes examined by electron microscopy. Letters in Applied
Microbiology. 19: 429-432.

Mannheim, C.H, Miltz, J. and Letzter, A. 1987. Interaction between polyethylene
laminated cartons and aseptic packed citrus juices. J. Food Sci. 52 :3 737-740.

Masuda, M., Saito, Y., Iwanami, T. and Hirai, Y. 1992. Effect of hydrostatic pressure on
packaging materials for food, p. 545-547. In C. Balny, R. Hayashi, K. Heremans
and P.Masson (ed), High pressure and biotechnology. Colloque INSERM / John
Libbery Co. Ltd. London.

Matsui, T., Nagashima, K., Fukamachi, M., Shimoda, M., and Osajima, Y. 1992.
Application of solubility parameter in estimating the sorption behavior of ﬂavor
into packaging ﬁlm. . J. Agric. Food Chem. 40:1902-1905.

Mermelstein, N. H. 1997. High-pressure processing reaches the US market. Food
Technology 51 (6): 95-96.

Mermelstein, N. H. 1998. High-Pressure processing begins. Food Technology 52 (6):
104-106.

Mertens, B. 1993a. Developments in high pressure food processing part 1. —
Internationale Zeitschrift fuer Lebensmittel Technik, Marketing, Verpackung-und-
Analytik. 44(3): 100-104.

Mertens, B. 1993 b. Developments in high pressure food processing part 2. —
Internationale Zeitschrift fuer Lebensmittel Technik, Marketing, Verpackung-und-
Analytik. 44(4) p. 182-187.

Mertens, B. 1993 c. Packaging aspects of high pressure food processing technology.
Packaging Technology and Sci. 63:31-36.

Mertens, B., and Deplace, G. 1993. Engineering aspects of high pressure technology in
the food industry. Food Technology. 47(6): 164-169.

Mertens, B. and Knorr, D. 1992. Developments of nonthermal processes for food
preservation. Food Technology. May.124-133.

Mertens, B. 1995. Hydrostatic pressure treatment of foodzequipment and processing,
p.135-158. Gould, G. W (ed.). In New Methods of Food Preservation, Blackie
Academic and Professional. New York, NY.

Meyer, R. S; Cooper, K.L.; Knorr, D.; Lelieveld, H. L. M. 2000. High-pressure
sterilization of foods. Food Technology; 54 (11):67-72.

Moshonas, M.G., and Shaw, PE. 1989. Quantitative analysis of orange juice ﬂavor
volatile by direct injection gas chromatography. J .Agric. Food Chem.35.l61-165.

Mohney, S M, Hernandez R J, Giacin J R, Harte B R, and Miltz. 1998. Permeability and
51

solubility of d-limonene vapor in creal package liners. J. Food Sci. 53(1).

Nachmanson, J. 1995. Packaging solutions for high quality foods processed by high
isostatic pressure. Europak 95: Dusseldorf, Germany. The 7th International
Conference on Plastics Packaging for the Food and Beverage Ind. p:390-401.

Nemphos, S. P., M. Salame, and S. Steingiser. 1986. Barrier polymers. In Encyclopedia
of Packaging Technology. M. Bakkar (ed.) Wiley&Sons Inc., New York.

Ochiai, S., and Y. Nakagawas. 1992. Packaging for high pressure food processing,
p.515-519. In C. Balny, R. Hayashi, K. Heremans and P.Masson (ed). High
pressure and biotechnology. Colloque INSERM / John Libbery Co. Ltd. London.

Ohlsson T. 1994. Minimal processing preservation methods of the future an overview.
Trends in Food Sci. Tech. 5 (11): 341-344.

Ohlsson, T. 1996. Minimal processing with thermal methods. International symposium
on minimal processing and ready made foods. SIK. Goteborg, Sweden.

Qin, B., Pothakamury, U.R., Vega. H., Martin, 0., Barbosa-Canova, G.V., and Swanson,
GB. 1995. Food pasteurization using high intense pulsed electric ﬁelds. Food
Technology. December. 55-60.

Paine, F .A. and Paine, H.Y. (1983) A Handbook of Food Packaging, Leonard Hill,
Glasgow, UK.

Patterson, M. F., and D. J. Kilpatrick. 1998. The combined effect of high hydrostatic
pressure and mild heat on inactivation of pathogens in milk and poultry. J. Food
Protection. 61(4): 432-436.

Paul, DR. and CB. Bucknall. 1999. Polymer Blends. Volume 2: Formulation. John
Wiley and Sons Inc., New York.

Palou, E., Lopez, M. A., G. Barbosa-Canovas, and G. B. Swanson. 1999. High pressure
treatment in food preservation. p. 532-576. In Rahman, S. (Ed.). Handbook of
Food Preservation. Marchel Dekker, Inc, New York, NY.

Robertson, G. L. 1993. Food packaging. Marcel Dekker. New York.
Rodriguez, F. 1984. Principles of polymer systems. Taylor and Francis.

Rudin, A. 1982. Basic principle of polymer molecular weights. In: The elements of
polymer science and engineering. Acedeic press, Inc., San Diego.

Rogers, C. E. 1985. Permeation of gases and vapors in polymers, chapter 2 in : Polymer
permeability, Elsevier Applied Science Publishers.

Schwartz, J. 1974. Polymer Material Science. Prentice-Hall, Inc., Englewood Cliffs, New
Jersey.

Sheng. D., and Smith, D.W. 1999. Analytic solutions to the advective contaminant

transport equation with non-linear sorption. International Journal for Numerical
and Analytical Methods in Geomechanics 23(9) 853-879.

Stern, S.A., and Trohalaki, S. 1990. Fundamentals of gas diffusion in rubbery and glass

52

polymers, Chapter 2: Barrier polymers and structures. American chemical society.

Swientek, R. J. 1992. High hydrostatic pressure for food preservation. Food processing.
9096.

Zimmerman, F. 1996. Squeezing Vacuum packaged foods for freshness. Packaging
strategies. 14(14). pz5.

53

CHAPTER 2

Effect of High Pressure Processing on Permeance of Selected High-

Barrier Laminated Films.

ABSTRACT

This study investigated the effects of high pressure processing (HPP) on the
barrier properties of 8 multilayer ﬁlms. Pouches made from the laminated ﬁlms were
ﬁlled with distilled water, heat sealed and then high pressure processed at 600 and 800
MPa for 5, 10 and 20 minutes at 45°C. Controls were similarly prepared but exposed to
atmospheric pressure. After processing, all pouches were emptied, dried, and their
oxygen, carbon dioxide, and water vapor permeance determined. All samples were tested
in quadruplicate. Films used in this study were PET/SiOx/LDPE, PET/A1203/LDPE,
PET/PVDC/nylon/HDPE/PE, PE/nylon/EVOH/PE, PE/nylon/PE, metallized
PET/EVA/LLDPE, PP/nylon/PP and PET/EVA/PET. Results showed that metallized
PET was most severely affected by HPP. For this material, permeance values for oxygen,
carbon dioxide, and water vapor showed increases as much as 150 %. Permeance

changes in the other materials were small when compared to metallized PET.

54

2.1 INTRODUCTION

New food processing methods are continually being developed to produce better
quality foods to meet consumers’ demands. These demands include less severely
processed, more natural, nutritionally healthier, and with food additives. One of these
new process is high pressure processing (HPP) (Palou et. al., 1999; Pre, 1992). HPP of
prepackaged foodstuff is steadily gaining ground as a method of food preservation,
worldwide. Current HPP technology applied to liquid and paste foods uses high
hydrostatic pressure in the range of 100-600 MPa for 2 to 10 min, to eliminate
microorganisms and deactivate some enzymes, depending on the food type and process
temperature (Mertens and Deplace, 1993; Palou et. al., 1999).

Although this treatment has been known as a potential food preservation
technique for over a century, only in the last few years there has been rapid development
in the engineering aspects of high-pressure technology. Thus, HPP provides the food
industry an alternative method to produce foods of high nutritional and sensory quality,
with more desirable texture and longer shelf life (Hayasi, 1995; Ledward, 1995). Foods
can be processed in bulk followed by aseptic ﬁlling, or as individual prepackaged
portions. High pressure processed foods have been marketed in Japan since the late
19805. Since then, interest has also developed in the United States and Europe. High
pressure processed foods have recently been introduced into these markets. During the
high pressure process, pressures are transferred instantly and uniformly throughout the
food system, even with air pockets within the package. Air pockets, however, should be

avoided due to the high compressibility of gases compared to liquids. As a result, HPP

55

will not be affected by the sample size and/or its geometry.

Previous research has shown that ﬂexible packaging is more suited to HPP than
rigid packaging (Mertens, 1993; Knorr, 1995). This is so because rigid packaging such as
metal cans or glass bottles tend to fracture or become distorted. Even though ﬂexible
packaging such as polymeric ﬁlms have been used to package foods processed by high
pressure, there is little published research on the effects of such pressures on their
chemical, mechanical and physical properties. Knowledge of any such effects would be
of importance to the food industry and government food regulatory agencies. Changes in
the permeation, migration, sorption, and package integrity, could affect negatively the
product shelf life and quality. Speciﬁc changes that may occur due to HPP within the
multilayer ﬂexible structures will depend on the ﬁlm composition and the HPP
conditions. Based on these considerations, we have evaluated the permeation, migration
and sorption of a series of high-barrier food packaging multilayer structures under a
variety of HPP conditions. In this study we report and compare results for the

permeability properties of the selected ﬁlms.

2.2. Materials and Methods

The ﬂexible structures investigated during this study are shown in Table 2.1.
Pouches measuring 10 cm x 10 cm were fabricated from roll-stock of these materials and
sealed using a Sencorp System, Inc. (Hyannis, MA) impulse heat sealer. For each
structure, the best conditions for sealing were obtained by adaptation of sealing methods
suggested by Lin et a1. (1998). All pouches were ﬁlled with 150 mL of distilled water,

then sealed with no headspace. For each test condition, two sets of pouches were

56

prepared, one set was maintained at latm and 23°C, and the other one was processed at
high pressures. This procedure was repeated twice (two blocks) for a total of four

repetitions for each data point. The HPP conditions were 600 and 800 MPa for 5, 10 and

20 min at 45°C. Each test pouch was placed in a 10.5 cm x 10.5 cm 25.4-micron outer
polyethylene envelope to protect the test pouches from direct contact with the HP liquid.
The envelope containing the test pouch was vacuum—sealed using a Multivac 021-336
impulse sealer (Busch, Switzerland). After processing the test pouches were removed
from the envelope. Control pouches were subjected to the same treatment except that
pressure was 1 atrn. Pouches were then emptied, opened, and dried before measuring the

gas transmission rate. As indicated, four replicates were tested for each treatment.

57

Table 2.1. The composition of the test ﬁlms used in this study.

 

 

Test ﬁlm structures Thickness (mil) Manufacturer

PP/ 30 um nylon-6/PP 4.6 Rexham Inc.

PET 12 um /A1203 300A /LDPE 2.5 GL-AE Toppan Co.
PET 12 um/ 310, 300A / LDPE 2.5 GL-AE Toppan Co.
Met-PET 12 um /30%VA EVA/LLDP 2.0 Cello-Foil Pro. Inc.
PET/PVDC/nylon/HDPE/PE 4.1 Rexham Inc.
PE/nylon/EVOH/PE 2.5 Cryovac
PE/nylon/PE 2.0 Cryovac
PET/4%EVA 2.0 Cello-Foil Pro. Inc.
PP (Single layer for comparison) 1.0 Tredegar Inc.

 

PP - Polypropylene

PET — Polyethylene terephthalate

Met-PET -— Metallized polyethylene terephthalate
PE — Polyethylene

EVOH — Ethylene-vinyl alcohol

LLDPE — Linear low density polyethylene
HDPE — High density polyethylene

EVA — Ethylene-vinyl acetate

PVDC — Polyvinylidene chloride .

Si0x — Silicon oxide

A1203 — Aluminum oxide

58

2.2.1. High-pressure apparatus

High pressure processing was done using a QFP-6 Tetra-Laval Quinta] high
pressure processor (ABB Autoclave System, Columbus, OH). This was located at the
NCFST/F DA facilities in Summit-Argo, Illinois. This equipment had a 1 L pilot scale-
processing vessel with an internal diameter of 6.0 cm by 18.8 cm in height, which

allowed processing of two pouches each time. It was designed for a maximum pressure of

890 MPa and an operational temperature range of 5-70 oC. During analysis of the

samples used in this study, the average time to attain the desired pressure was 2.3 $0.25
min. The temperature at processing peaked to a maximum of 50°C but was maintained at

45 0C for the major part of each test run. The hi gh-pressure transmission ﬂuid used in this
equipment was Houghto-Safe 620-TY (Houghton International, Valley Forge, PA), a
glycol/water mixture. Processing conditions were as follows: two enveloped pouches
were placed within the vessel ﬁlled with transmission ﬂuid, clamped within the high-

pressure chamber and then pressure processed.

2.2.2. Permeance

The outputs of the permeation apparatus were obtained either as steady state transmission
ﬂow rate Fv for oxygen and carbon dioxide, or steady state mass transmission rate FM for
water vapor. Units of Fv are cm3/m2-d for oxygen and carbon dioxide, and g/mz-d for FM
of water vapor. The permeance (R) instead of the permeability coefﬁcient is reported in
this work for the multilayer ﬁlms because of the non-polymeric nature of the metallized,

aluminum oxide, and silica oxide coated layers in some of the ﬁlms studied. Permeance

59

was calculated as (Hernandez and Gavara, 1999):

12:5- (1)

Ap

Where F represents Fv or FM and Ap is the partial pressure difference across the test ﬁlm.
Because the area of each pouch was smaller than the required Permatran cell area,
each ﬁlm sample was mounted on a self-adhesive supporting 12 x 12cm paper/aluminum
foil mask with a central circular opening of 5.00 cmz. The mounted ﬁlm was placed
between the two half-cells of the respective permeation apparatus for testing. This
procedure was followed for all measurements. Prior to running the test, both half-cells

and the sample ﬁlms were pre-conditioned for at least 2 h in a dry stream of nitrogen gas.

2.2.3. Water vapor transmission rate

The water vapor transmission rate (WVTR) of the test ﬁlms was determined using
a Permatran-W 3/31 Tester (Modern Controls, Inc., Minneapolis, MN), according to
ASTM F 1249-90. Measurements were carried out at 37.8 i 0.5 0C. The permeant high-
pressure side of the cell was ﬂushed with a nitrogen gas stream of about 10 mI/min
humidiﬁed at 85% i1% relative humidity (RH). The vapor was generated by ﬂowing
nitrogen gas into dionized water at 1.177 atm within the instrument. When this stream
contacted the ﬁlm it was at 1 atm of pressure. The permeant low pressure side of the cell
was ﬂushed with nitrogen carrier gas at 100 mL/min and 0% RH and also at 1 on of
pressure. Therefore, the test was performed under a total pressure of 1 atm at both sides

of the ﬁlm. An infrared detector quantiﬁed the permeated water vapor molecules. The

60

 

 

 

ga.

apparatus was connected to a desktop computer. Output values were expressed as the

steady state water vapor transmission rate (WVTR), calculated using Permw® -

Windows® computer software. Polyethylene terephthalate (PET) ﬁlm of standard WVTR

was used to verify the operation of the Permatran W3/31.

2.2.4. Oxygen transmission rate

The oxygen transmission rate of the test ﬁlm was determined in a 2-station
Mocon Ox-TRAN® 200 (Modern Controls Inc., Minneapolis, MN), according to ASTM
D 3985-81. The tester was equipped with a coulometric oxygen sensor sensitive to the
0.01 cm3/m2-d. Throughout the test, the permeant high-pressure side of the cell was
swept with air at 20 cc/min at 1 atm. The partial pressure of oxygen was 0.21 atm. The
low-pressure side of the cell was swept with pure nitrogen gas containing 1% hydrogen at

atmospheric pressure at 30 cc/min, which conveyed the oxygen permeated to the detector.

Measurements were carried out at 25 d: 1°C. The 0x —TRAN 200 was connected to a
desktop computer. Output values were expressed as the steady state oxygen transmission
rate in g/mz-d using DOS computer software. Polyethylene terephthalate (PET) ﬁlm of

standard oxygen permeability was used to verify the machine conditions.

2.2.5. Carbon dioxide transmission rate

Carbon dioxide permeance was measured using a Mocon Permatran C-IV® carbon
dioxide permeability tester (Modern Controls, Inc., Minneapolis, MN), using the static
accumulation method which is recommended for high barrier ﬁlms. Pure carbon dioxide

gas of a ﬂow rate of 80 cc/min was swept through the high-pressure permeant side of the

61

cell. Permeated carbon dioxide was canied to the detector by nitrogen carrier gas at a
ﬂow rate of 200 cc/min. An infrared sensor interfaced with a strip-chart recorder
measured the CO2 concentration. Tests were conducted at 23 :t 1°C . The carbon dioxide

transmission rate Fv was obtained as follows:

 

F. = ' (2)

where V is a constant calibration volume of 0.0248 mL, S is the inﬁ'ared response peak
corresponding to V, H is the infrared response peak of the permeated C02 accumulated

in the detecting cell, A is the 5.00 cm2 area of the ﬁlm, and t is the accumulation time.

2.2.6. Statistical analysis

Experiments were planned to evaluate the combined effects of the pressure (600
and 800 MPa) and time (5, 10, and 20 min) factors on the barrier behavior of selected
ﬁlms. Permeance values were obtained in 2 trials consisting of 2 replicates each. A
randomized complete block design was applied to the control samples (1 atm, 0 time) and
samples processed at conditions determined by the arrangements of 600-5, 600-10, 600-
20, 800-5, 800-10, and 800-20. Data collected were analyzed using a least squares mean
generalized linear model (LSM-PROC GLM) in the statistical analysis software program
(SAS Institute, Inc., 1990). The model assumes a ﬁxed relationship between factors,
differences between factors, and pair-wise differences between all combinations of

factors. Statistical signiﬁcance was deﬁned as p<0.01.

62

2.3. RESULTS and DISCUSSION
2.3.1.0xygen permeance

Figures 2.1 and 2.2 show the oxygen permeance for each ﬁlm at 600 MPa and
800 MPa and at 5, 10, and 20 min respectively. It can be seen that PET/SiOx,
PET/A1203/PE, PET/EVA, PP/nylon/PP, and especially Met-PET showed differences in
permeance after treatment by HPP when compared with their untreated counterparts.
These differences are conﬁrmed by the statistical analyses at a 99% conﬁdence level.

The results obtained for Met-PET showed signiﬁcant differences (p<0.01) in
oxygen permeance between the HPP treated and untreated ﬁlms. There were also
signiﬁcant differences between the ﬁlms treated at 600 MPa for 5 and 10 minutes and
those ﬁlms treated at 800 MPa for 5, 10 and 20 minutes. Differences in permeance
between Met-PET ﬁlms treated at 600 MPa for 20 minutes and those treated at 800 MPa
for 5 and 10 minutes, was not signiﬁcant. There were also no signiﬁcant differences in
oxygen permeance between the metallized PET ﬁlms treated for 5 min when compared to
those treated for 10 minutes at both 600 and 800 MPa. Changes in permeance over the
untreated samples are presented in Figures 2.3 and 2.4. These ﬁgures show that the
largest increase in permeance (90%) was observed in Met-PET ﬁlms treated at 800 MPa
for 20 minutes.

Results for PP/nylon/PP Show that there were signiﬁcance differences in oxygen
permeance between materials treated at 800 MPa for 10 and 20 minutes when compared
to the untreated materials. Changes in permeance caused by HPP at 600 MPa and 800
MPa for 5 minutes, were not signiﬁcant when compared to the untreated controls. Figure

2. 4 also shows the change in permeance for HPP treated PP/nylon/PP.

63

Although small in percent change, the statistical analyses showed signiﬁcant
increases in oxygen permeance for PET/SiOx, PET/A12O3/PE and PET/EVA. Maximum
percent change in permeance for these materials shown in Figures 2.3 and 2.4 were at
800 MPa for 20 minutes. The respective percent increase were 10, 7 and 9%.

The oxygen permeance for PET/PVDC/nylon/HDPE/PE, PE/nylon/EVOH/PE,
PE/nylon/PE, and PP was statistically unaffected by the HPP treatment. Comparing all 9
ﬁlms, PE/nylon/PE showed the highest oxygen permeance value, which was signiﬁcantly
different from the other ﬁlms. As expected, the lowest permeance values were seen in
ﬁlms with SiOx, PVDC, A1203 and EVOH, since these components are high barrier
materials. Although there were small changes in permeance between the untreated and
treated PET/SiOx, PET/A1203/PE ﬁlms (less than 10%), they are nevertheless higher than,
PE/nylon/EVOH/PE and PET/PVDC/nylon/HDPE/PE which are exclusively polymeric
materials. This may indicate that inorganic base high barrier ﬁlms are more susceptible
to high-pressure treatment than polymeric ﬁlms. This observation is further supported by
the unaffected values of single-layer PP ﬁlm.

In the case of Met-PET, permeance increased as a result of the HPP treatment,
indicating that possible stretching of PET did not correspond to the metallized layer. The
oxygen permeance changes observed in PP/nylon/PP were surprisingly high considering
that no change was observed in PE/nylon/PE. Possible reasons for this result may be
differences in material morphology and processing conditions. The PP/nylon/PP ﬁlm was

approximately twice as thick as the other ﬁlms.

64

   

E

vi lAtm. Press.
E l 5 min HPP
E 10 .10 .

,_ mIn HPP
% [320 min HPP
’2

E.

3 5

C

(I

c

E

o

n.

o I]

? Q . 1-
+6“? \0‘8 6090
(,(m (not «a? “9,,
9 ‘3
‘5? E90 we
99° 60°

 

.00“?

Figure 2.1. Oxygen permeance of multilayer ﬁlms before and after HPP, at 23°C

15 -
I 1 atm
‘{ I5 min HPP
I10 min HPP
I .
10 , .20 mm HPP

Permeance (th0“) m’(srpym'.s.Pa

 

9 9 9 9
00“)? 00“)? 09“? 0V“? 036 0399 0d? 0‘8
«9°? at”? 26““) 96°19 0‘” 00‘” 0‘” 09°
60° 00 00"}?6 0°“?3 500 $0 50° 0°
6 s

Figure 2.2. Oxygen permeance of multilayer ﬁlms before and after HPP, at 23°C.

65

95-

85..

Percent change In Penneance

65:

I96 change 5 min
I96 change 10 min
I96 change 20 min

75-

55 4
4s 4
3s «

25%

15-

5

.5

Q9

Figure 2.3.

1

Percent change In Permeance

91"“

.09”

Figure 2.4.

 

Q Q
«4"? gegwad’k My valet“ Weave! ”WWW“

.0: We .00“ 9,... .0») .6»

Percent change in oxygen permeance of multilayer ﬁlms before and after

HPP, at 23°C.

  
 
  
 

00
so;
so-

I%change§min
70' I°/ochange 10min
60»? I°/ochange20min

  
 
 

PM 9906168?

M” 500“”

Percent change in oxygen permeance of multilayer ﬁlms before and after

HPP, at 23°C.

66

2.3.2.Water vapor permeance

The high-pressure process affected the water vapor permeance of PET/SiOx,
PET/Al203/PE, PET/PVDC/EVA, PP/nylon/PP and metallized PET (Figures 2.5 and 2.6).
The statistical analyses showed that there were signiﬁcant differences between the
control ﬁlms and the ﬁlms treated at 600 and 800 MPa. The effects of HPP treatment on
the water vapor permeance of the other ﬁlms were insigniﬁcant. The percent changes in
water vapor permeance for these HPP treated ﬁlms are shown in Figures 2.7 and 2.8.

Signiﬁcant increases (p<0.01) in water vapor permeance for PP/nylon/PP were
seen in ﬁhns treated at 600 MPa for 10 and 20 minutes and at 800 MPa for 20 minutes
when compared to the control in each case. For PET/SiOx, signiﬁcant changes between
the control and the treated ﬁlm were observed for ﬁlms pressured at 600 MPa for 20
minutes and at 800 MPa for 10 and 20 minutes. Signiﬁcant increase in permeance caused
by the increase in treatment times from 5 to 10 minutes at 600 MPa and from 5 to 20
minutes at 800 MPa were also observed for the PET/SiOx, Similar results were also
obtained for the PET/Al203/PE and PET/EVA materials. However, for PET/EVA,
signiﬁcant differences in permeance were also seen between the control and the ﬁlms
treated at 600 MPa for 5 and 10 minutes.

As in the case of oxygen, the largest changes in water vapor permeance for all the
materials were seen in the metallized PET. Figure 2.7 shows a change of approximately
150% for that material treated at 800 MPa for 20 minutes. This large change in
permeance resulted from the high-pressure treatment were much higher than change in

the permeance for oxygen and carbon dioxide. For the other materials, changes in water

67

vapor permeance were generally lower than those obtained for oxygen and carbon
dioxide.

Relatively high permeance values were obtained for PE/nylon/EVOH/PE. Both
EVOH and nylon are hydrophilic and we should expect relatively high water permeance
values even though they have relatively low permeability to oxygen at dry conditions.
When exposed to moisture, EVOH and nylon materials can show increased oxygen
permeance (Hernandez, 1994).

The water vapor permeance of PP/nylon/PP compared to PE/nylon/PE is probably
due to differences in sample themselves or the individual layers and overall thickness.
As expected, structures containing PVDC, $0,, and A1203 had low water permeance

values compared to nylon, PET and EVA based ﬁlms.

68

‘ IAtm. Press.

‘ I5 min HPP
20 i I10 min HPP
I I20 min HPP

   
  

Permeance out 0") kglm’.s.Pa

5i
III!-
oi , . a

9? V .01» .0‘1- R
(«1‘6“ “$00? 65c» Qéﬁ P903
“90?? “96?? (99‘3‘93 “$96 699‘“ 0
50° .560 600‘»? $000?

Figure 2.5. Water vapor permeance of multilayer ﬁlms before and after HPP, at 378°C.

 

 

30
I Am. Press.
25 I 5 win HPP
I: » - I10 min HPP
“'- U 20 min HPP
% 20
.3
2° 1 5
E
0
g 10
E
0
°- 5
o I]
Q‘ Q Q?
”50‘? “60‘? “or“? \loY“ “$0“? “AGE
9“ e“? 00" 00“” v9 c?)
“ye? “are? 961°» «1‘ 00"?” 00“,?” (Nye
(:00 $30 06".?” 90an P P ‘50
6 'b

Figure 2.6. Water vapor permeance of multilayer ﬁlms before and after HPP, 378°C.

69

‘ I96chan995mln

 

 

D96 change 10 min
g as l I96 change 20 min
3 55 I
.E
0
2 45 (
ﬂ
6
E 35 l
2
n. 25 1‘
15 1‘
5 _
h . , , ,
-5 0386 (v, e
60°C“! .f’c MM +6.60“? a“? a“ ”at“ we”?
(,DQ‘RQQ $00939? 96H“ ”99)“ 6&th.3? @813? 6639?” w‘ﬁﬁ?
a”
6*
Figure 2.7. Percent change In water vapor permeance of multilayer ﬁlms before and after
HPP, at 378°C.
160 -
150 J,
140 . I% change 5 min
130 l I% change 10 min
3 120 -‘ I% change 20 min
5 110 4
E
a 100 1‘
5 9° ‘
3 30 I
C
2 7o 1
U
2 so I
40 .
so

‘§-_,¢_d# .l.

9 Q? .91- .01- (a e
\0 \o‘fd“ 9?,“9 96“?» $101? 0'51?
5?? 99?? 9° 99° v?ﬂ 9 99°
66)“? $009 50°“ 6,00 6&‘Ra w‘ﬁg 6GP

 

Figure 2.8. Percent change in water vapor permeance of multilayer ﬁlms before and after

HPP, at 378°C.

70

2.3.3. Carbon dioxide permeance

Permeance values of carbon dioxide through ﬁlms (except PP/Nylon/PP) were
from 2 to 5 times higher than for the respective oxygen permeance (Figures 2.1, 2. 2, 2. 9,
and 2.10). The CO2/02 permeance ratio was 3.8 for the single-layer polypropylene. These
values are in very good agreement with the ratio of C02/O2 permeability coefﬁcients for
single layer polymers (Hernandez, 1997). The C02/02 permeance ratio of PP/Nylon/PP,
however, was 0.4 which is much lower than expected. The statistical analysis showed
that there were signiﬁcant differences Q)<0.01) between all the Met-PET ﬁlms treated by
HPP for 600 and 800 MPa compared to their untreated counterparts. For those ﬁlms
treated at 600 MPa, increasing the treatment time from 5 to 20 min resulted in
signiﬁcantly increased carbon dioxide permeance. At 800 MPa, increasing the treatment
times from 5 to 10 or 20 minutes had no signiﬁcant effect on carbon dioxide permeance.
However, the Met-PET pressure treated ﬁlms at 800 MP3 for 5, 10 and 20 min had
signiﬁcantly higher permeance than the same material treated at 600 MP3 for 5 minutes.
Films treated for 800 MPa for 20 minutes had signiﬁcantly higher permeance than those
treated at 600 MPa for 10 and 20 minutes. Thus, increasing treatment pressure for Met-
PET resulted in more signiﬁcant change in carbon dioxide permeance compared to the
effect of changing pressure times.

The results obtained for PP/nylon/PP showed that the carbon dioxide permeance
for this material was signiﬁcantly increased only pressure treated ﬁlm for both 600 and
800 MPa at 20 minutes when compared to the controls. Both treatment pressures at 20

minutes had the same effect on permeance for PP/nylon/PP because there was no

71

signiﬁcant difference (p<0.01) in permeance for carbon dioxide at 600 when compared to
800 MPa for 20 minutes. Thus, increasing the pressure from 600 to 800 MPa had no
signiﬁcant effect on permeance for 20 minutes of treatment. Similar results were obtained
for PET/EVA and PET/Al203/PE. PET/EVA and PET/Al203/PE were signiﬁcantly
different between 600 and 800 MPa for 20 minutes and control

The results obtained for PET/SiOx showed that both increase in treatment pressure
and in processing times produced signiﬁcant increase in carbon dioxide permeance.
Signiﬁcant differences in permeance were seen after the material was treated at 600 MPa
for 20 minutes and at 800 MPa for 10 and 20 minutes when compared to the control.

Even though signiﬁcant differences in carbon dioxide permeance were observed
in all materials treated by high pressure, these changes were small when compared to

metallized PET (Figures 2. 11 and 2. 12).

72

 

25,

IAh'n. Press.

 

 

 

A: 20 I5 min HPP
,3! I10 min HPP
g I20 min HPP
.2
£9, 15
E
’9.
g 10
I
2
3
E
O
l :I] I]
Q Q (o (o
Le? at"? 40“" of?e 9°“? 1° " er" a“?
e“ <\ a9 a a“ a“ an a
“so? “839?, 90°F, Qaﬁxo 600999? 600039? “9‘3? “99?
e a 50° 9,00
50° $00 600‘}? 0‘)?

Figure 2.9. Carbon dioxide permeance of multilayer ﬁlms before and after HPP, at 23°C.

25

20 .
IAtm Press.
I5 min HPP
I10 min HPP

15 1 12120 min HPP

Permeance (Rx10'5) m’(STP)Im’.s.Pa

? Q 0‘! .01 Q Q 3
\0‘”? \OOR Qé‘\%\ 6‘9 103? 7535‘? 0‘96 0‘??’
N we I» \\’° E at
“90?? “9'5? 909‘”? $330 13?,“ a? Q68 Boo‘pQ‘D $00“?
600 $00 6 0° 600‘)? $009?

Figure 2.10. Carbon dioxide permeance of multilayer ﬁlms before and after HPP, at
23°C.

73

751

65 -'
I96 change 5 min

55 I% change 10 min

     
  

% I% change 20 min
i 45 5
g. 35 9
g 25 ‘;
E
15 1
5 1
fi- . rte —-.T.—___T_% ,iﬂ
gaff” efwe‘éwfw M M ewe 960'”
V v0 9’
509”” 29°“, 500“” o ﬂew“ 129°” 509”” 6”“ 90°”
Figure 2.11. Percent change in carbon dioxide permeance of multilayer ﬁlms before and
after HPP, at 23°C.
75 -
I % change 5 min
55 . D96 change 10 min
I 96 change 20 min
3 55 ‘
§ 1
E 45 ~
g I
a as .
2
a
15 .
. c . é
a? e 6 “$094 ”MVG 9090‘?
663“?“ Q 96‘ 630" M

Figure 2.12. Percent change in carbon dioxide permeance of multilayer ﬁlms before and

after HPP, at 23°C.

74

2.4. CONCLUSION
From the results obtained during this study, it can be concluded that 1) for the

inorganic-coated structures, 800 MPa and longer processing times seem to have a more
pronounced effect on permeance change than 600 MPa and shorter exposure times. 2)
The metallized PET was most severely affected by the high pressure processing. 3) The
most severe effects were seen in changes to the water vapor transmission rate because of
the smaller molecule size when compared to oxygen and carbon dioxide. 4) Apart from
metallized PET, changes in permeance occurring in the other materials were fairly small,
even though statistically signiﬁcant in some cases. 5) Increases in permeance in
structures other than Met-PET were less than 12%. Therefore, these changes may have
small or no impact on the shelf life of the packaged foods. This, the structures used in this
study may be well suited for high pressure processing. This was indeed the case as
reported by Masuda et a1. (1992) and Barnes (1992) who studied the effects of HPP at
400 and 600 MPa respectively, and found that the barrier materials investigated were not

severely affected by those pressures.

75

2.5 REFERENCES

Barnes, R]. 1992. Effects of high-pressure sterilization on packaging. Food, Cosmetics
and Drug Packaging. April 1992. p. 1-3. Elsevier Science Publisher Ltd.

Code of Federal Regulations 21 113.60. 1999. Subpart D. Control of component, food
product containers, and in-process materials. p.247-249. US. Government
Printing Ofﬁce, Washington. DC.

Hayasi, R. 1995. Advances in high pressure food processing technology in Japan. Food
Processing: Recent Developments, Ganonkar, A.G. (Ed.), p. 85. Elsevier, New
York, NY.

Hernandez, R. J. 1994. Effect of water vapor on the transport properties of oxygen
through polyarnide packaging materials. J. Food Eng. 22:495-507.

Hernandez, R. J. 1997. Food packaging materials, barrier properties, and selection. Ch 8.
In Handbook of Food Engineering Practice, ValentaS,K.J., Rolstein, E., Singh,
R.P. (Ed), p. 356. CRC Press, Boca Raton-New York.

Hernandez, R. J. and Gavara, R. 1999. Plastic packaging: methods for studying mass
transfer interactions. p. 5-31. Pira International, Leatherhead, United Kingdom.

Knorr, D. 1995. Hydrostatic pressure treatment of food: Microbiology. Ch 8. In New
Methods of Food Preservation, Gould, G. W (Ed.), p. 159-176. Blackie
Academic and Professional. New York, NY.

Ledward, AD. 1995. High pressure processing - the potential. Ch 1. In High Pressure
Processing of Foods. Ledward, D.A., Johsnton, D.E., Eamshow, R.G. and
Hasting, A.P.M. (Ed). p. 1-5. Nottingham University Press., Nottingham,
England.

Lin, R.C., King, RH. and Johnson, M. 1998. Examination f containers for integrity. Ch
22. In Bacteriological Analytical Manua,l 8th Ed. p. 22.37-22.42. NFPA,
Washington, DC.

Masuda, M., Iwanami,T. and Hirai.Y. 1992. Effect of hydrostatic pressure on packaging
materials for food. Ch 4. In High Pressure and Biotechnology, Balny, C.,
Hayashi, R., Heremans, K. and Masson, P. (Ed.), p. 545-548.
Montrouge:Inserm/John Libbey Eurotex Ltd.

Mertens, B. 1993. Packaging aspects of hi gh-pressure food processing technology.
Packaging Technology and Science. Vol. 6: 31-36.

76

Mertens, B. and Deplace, G. 1993. Engineering aspects of high- pressure technology in
food industry. Food Technology. 47(6): 164-169.

Palou, E., Lopez-Malo, A., Barbosa-Canovas, G. and Swanson, GB. 1999. High pressure
treatment in food preservation. Ch 19. In Handbook of Food Preservation,
Rahman, S. (Ed.) p. 532-576. Marchel Dekker, Inc, New York, NY.

Pre, G. 1992. Trends in food processing and packaging technologies. Packaging
Technology and Science Vol 5: 265-269.

SAS Instute, Inc. 1990. SAS/STAT User’s Guide, version 6. Statistical Analysis Systems
Institue, Inc., Cary, NC.

Swanson, B.G. 1989. High pressure process. Ch 4. In Nonthermal Preservation of Foods,
Barbosa-Canovas, Gustavo V. Ed, p. 66-100. Marcel Dekker, Inc., New York,
NY.

77

CHAPTER 3

Study of High Pressure Processing Effects on Flexible Food Packaging
Structures by Mechanical Analysis, Scanning Electron Microscopy, and

Ultrasonic Imaging

ABSTRACT

The effects of high pressure processing (HPP) on the mechanical and physical
characteristics of 8 hi gh-barrier multilayer ﬁlms were investigated. This study also
investigated the presence of micro defects in the ﬁlms. These defects may have been
caused by HPP. The ﬁlms tested during this study were PET/SiOx/LDPE,
PET/A12O3/LDPE, PET/PVDC/nylon/HDPE/PP, PE/nylon/EVOH/PE, PE/nylon/PE,
metallized-PET/EVA/LLDPE, PP/nylon/PP, and PET/PVDC/EVA. In addition, PP was
evaluated for comparison purposes. Pouches made from the ﬁlms were ﬁlled with
distilled water, sealed, then pressure processed at 600 and 800 MPa for 5, 10, and 20
minutes at 45°C. Pouches kept at atmospheric pressure were used as control. Prior to and
after HPP, tensile strength, percent elongation, modulus of elasticity, scanning electron
microscopy (SEM), and scanning acoustic microscopy (C-SAM) measurements were
taken for each ﬁlm. Results showed that no signiﬁcant changes in tensile strength,
elongation and modulus of elasticity of the ﬁlms were detected. However, physical

damage to the metallized-PET ﬁlms was identiﬁed by SEM and C-SAM analyses.

78

3.1. INTRODUCTION

High pressure processing (HPP) is now used in conjunction with other novel, non-
thermal food processing techniques such as pulsed electric ﬁelds, irradiation (including
pulse light, electron beam, ultra violet light, gamma and x-rays) ultrasound and ozone
treatment for food preservation (Cherry, 1999; Liangi, 1999; Sizer and Balasubrarnaniam,
1999; Thayer and Rajkowski, 1999). Interest in these technologies has been gaining
ground within the United States because of consumers’ demand for higher quality foods
with more homestyle taste and appearance(Karel, 2000; Sloan, 1999). Applied to foods
HPP in the range of 400 to 850 MPa has been shown to deactivate enzymes and reduce
bacterial load (Aleman et al. 1998; Anathy et a1. 1998). Since it requires less heat than
traditional thermal techniques such as retorting and pasteurization, HPP leaves the food
with little textural change and less vitamin and ﬂavor loss. HPP technology offers the
food industry the opportunity to develop food with more convenience, safety and
extended shelf life (MacDonald et al. 2000). The recent introduction of continuous HPP
systems in the United States has made it possible for processors to treat pumpable foods
at commercial machine speeds followed by aseptic packaging. However, batch HPP
systems are also available and can be used to treat non-pumpable foods and other
prepackaged liquid and semi-solid foods in small portions. HPP has also shown to be an
environmentally friendly alternative process because it uses less energy compared to
thermal processing techniques (Denys and Hendrickx, 1999; Prestamo and Arroyo,
1998). The use of plastic-based ﬂexible packaging ﬁlms has allowed the application of
high-pressure processing to pre-packaged foods. These materials have been shown to

withstand the process without visible signs of integrity loss (Barnes, 1992). However,

79

there is limited published data on the effects of HPP on the physical, mechanical, and
package integrity characteristics of packaging materials. HPP treatment of prepackaged
foods may cause defects in certain plastic packaging structures, which could result in loss
of package integrity or at least compromise its barrier and safety characteristics.

Rigid packaging is not suitable for HPP since it has been shown to be susceptible
to fracturing or distortion when exposed to high pressures (Barnes, 1992).

One of the most important factors that has contributed to the success of plastic
ﬁlms and sheets for food packaging is the availability of multilayer structures produced
either by lamination or coextrusion. A ﬂexible multilayer structure used for pre-packaged
food HPP must have sufﬁcient ﬂexibility and resilience, and must resist delarnination
between layers during the compression process. Flexible structures in which HPP
produces the formation of micro pockets in some of the layers may eventually
compromise the safety of the package. In the converting industry, different materials are
used to produce laminated structures. These include polymers such as PVDC, metals such
as aluminum used for vapor deposition on plastic ﬁlms like PET, and inorganic coatings
such as silicon and aluminum oxides also used to coat plastic ﬁlms. If the components of
a multilayer structure show widely differing compressibility and resilience behavior
under HPP, the ﬁlm may exhibit a loss of integrity. For food products with extended
shelf-life, these changes may be precursors to major food safety and quality issues.

Changes in the integrity of a multilayer ﬁlm may be very small and difﬁcult to
detect. One way to study them is by using molecular probes such as permeation to gases
and vapors. Other methods include acoustic imaging and electron microscopy. Scanning

electron microscopy (SEM) has been used successfully to visualize evidence of

80

mechanical deformation on the surface of various plastics (Choudry et al. 1998).
However SEM gives information about the surface rather than inside of a multilayer
materia.

C-mode scanning acoustic microscope (C-SAM) uses sound waves instead of
light to produce images, and has the documented ability to detect, classify, and accurately
reproduce the integral structure of opaque materials or components using high frequency
ultrasound in the range of 5 to 500 MHz. C-SAM allows scanning and imaging of
heterogeneous materials such as multilayer structures samples based on the intensity of
acoustic waves reﬂected by the various constituents of the sample. This is done at
variable depth and without destroying the test specimen. Since reﬂection intensity is
based on impedance contrast, a change in the elastic properties between two constituents
or within one constituent can be easily detected. Ultrasound is extremely sensitive to air
gaps and gaps as small as 10'7m can be detected. C-SAM uses pulse-echo technology in
which a focused beam of ultrasound is pulsed into a sample. Reﬂections of the ultrasound
beam are then received from the sample and processed by the electronics according to
their phase amplitude. Ultrasound techniques have been used for detecting and
visualizing hidden defects such as voids, cracks, folds, lamination, delamination and
porosity in solid samples (Chen et al. 1991; Hafsteinsson et al. 1989; Ozguler et al. 1998;
Povey and McClements 1988; Safvi et al. 1997).

In the present work we report the results of the effects of HPP on mechanical
behavior by measuring the tensile properties, and use of SEM and C-SAM techniques to
visualize the microstructure of the ﬂexible ﬁlms. These results are compared to the

permeability results on the same structures from chapter 2.

81

3.2. MATERIALS & METHODS

Table 3.1 shows the multilayer ﬁlms investigated during this study. These ﬁlms
were used to prepare 10 x 10 cm pouches using a Sencorp System, Inc. (Hyannis, MA)
impulse heat sealer. The pouches were fabricated, sealed, ﬁlled with distilled water and

high pressure processed as described in chapter 2. For each test condition, two sets of

pouches were evaluated, one set was maintained at 1 atm and 23 iIOC (control), and the
other processed at high pressures. Four replicates were run for each material and each

replicate was analyzed twice. The HPP conditions were 600 and 800 MPa for 5, 10 and

20 min at 45°C. After HPP, all pouches were emptied, opened, and dried before analysis

for mechanical strength and electron microscopy. Control pouches were immersed in

distilled water at 50°C for 20 minutes but maintained at 1 atm prior to testing.

3.2.1. High-pressure apparatus

High pressure processing was carried out using a QFP-6 Tetra-Laval Quinta] high
pressure processor (ABB Autoclave System, Columbus, OH) located at the National
Center for Food Safety and Technology (NCFST) facilities in Summit-Argo, Illinois.
This equipment had a l L pilot-scale processing vessel with an internal diameter of 6.0

cm by 18.8 cm in height. It was designed for a maximum pressure of 890 MPa and an

operational temperature range of 5-700C. During analysis of the samples used in this

study, the average time to attain the desired pressures was 2.3 i 0.25 min. The

temperature at processing peaked to a maximum of 50°C but was maintained at 45 °C

82

(i0.5 0C) for the major part of each test run. The high-pressure transmission ﬂuid used in
this equipment was Houghto-Safe 620-TY (Houghton International, Valley Forge, PA), a
glycol/water compound. For each run the following procedure was applied: 1) the pouch

sample was immersed in the transmission ﬂuid, 2) the pressure chamber was secured by a

built-in locking device, and 3) the high pressure was activated.

3.2.2. Scanning Electron Microscopy

For this study, environmental scanning electron microscopy (ESEM) was used
because of its ability to reveal sharp surface topography images of a specimen. The
equipment used was an Electro Scan 2020 scanning electron microscope (Electroscan,
Boston, MA). The test ﬁlms were prepared by cutting 2 cm x 3 cm strips from each
material treated by HPP and from the controls. Each strip was mounted onto the
microscope specimen chamber by attaching it on a sample holder and positioning it along
the electron beam pathway according the manufacturer’s instructions. The pressure of the
specimen chamber was maintained at 380 Pa while the electron gun chamber was kept at
1.33 x10‘5 Pa. The acceleration voltage was set at 12 kV for a working distance of 8 mm.

During adjustment of the magniﬁcation the acceleration voltage was kept constant.

3.2.3. Scanning Acoustic Microscope

Scanning acoustic microscopy images were obtained on a Sonoscan D9000 C-
mode Scanning Acoustic Microscope (C-SAM) (Sonoscan Inc. Bensenville USA). The
C-SAM uses "pulse-echo" technology, which includes a 100-230 MHz ultrasound beam,

and allows for detection of internal damage and/or delamination in the multilayer

83

structures. C-SAM in-depth information supplements the SEM superﬁcial images.
Samples were placed in the sample holder under the acoustic beam. Reﬂections of the
sound were captured by a pulser-receiver and digitally processed according to their phase
and amplitude. The images were constructed by making each pixel correspond to a data
point in the sample and the phase/amplitude information from the reﬂections was
assigned a pixel value. The number of pixels per image was 1024 x 920.

Images of both'HPP treated and control (untreated) ﬁhn samples were obtained using a
230 MHz ultrasound beam. The resolution of the transducer was 0.11 mm and the ﬁeld
of view for the images was 10.4 x 7.9 mm. Voids and delaminations block the

transmission of ultrasound and appear in the images as bright white areas.

3.2.4. Tensile stress, strain, and modulus of elasticity

Tensile strength (TS), percent elongation at break (E), and modulus of elasticity
(MOE) for each material (treated and controls) were measured using a Model 4201
Instron® (Instron, Canton, MA). From each material, two sets of 2.5 cm x 10.0 cm
sample strips were prepared. One set was taken along the machine direction and the other
along the cross directional orientation of each ﬁlm. Film thickness (see Table 1) was
measured using a micrometer model 549 TMI (Micrometer Testing Machines, Inc.,
Amityville, NY). The Instron tester was ﬁtted with a 1 kN tension load cell. The jaws
were set at 5 cm apart and the crosshead speed adjusted to 50 cm/min. All measurements
were carried out at 23 °C (i: 1 °C), and at 50% relative humidity. All samples were pre-
conditioned by exposing them to these conditions for 24 hours prior to testing. Tensile

strength was calculated by dividing the maximum load by the cross-sectional area. Strain

84

at break was calculated by dividing the increased length at the moment of rapture by the
initial length of the specimen. Modulus of elasticity was calculated from the slope of the

elastic portion of the tensile stress versus strain curve.

3.2.5. Statistical analysis

This research investigated the effect of pressures (600 and 800 MPa) and
processing times (5, 10, and 20 min) on the mechanical properties of the selected ﬂexible
materials. Mechanical properties were evaluated by analyzing 4 replicates of each ﬁlm
sample. Each test was repeated once. Each sample was analyzed for the effect of pressure
and time on tensile strength, percent elongation and modulus of elasticity. The results
obtained from these analyses were compared with the outputs obtained from the electron
microscopy imaging of the sample materials. A completely randomized block design was
applied to the controls and the samples processed at 600 MPa for 5 minutes (600-5), 600
MPa for 10 minutes (600-10), 600 MP3 for 20 minutes (600-20), 800 MPa for 5 minutes
(800-5), 800 MPa for 10 minutes (800-10), and 800 MPa for 20 minutes (800-20). The
data collected were analyzed using a least square means generalized linear model (LSM-
PROC GLM) of the statistical analysis software program (SAS, 1990). The model
assumed a ﬁxed relationship between factors, differences between factors, and pair-wise
differences between all combinations of factors. Statistical signiﬁcance was deﬁned at p

< 0.01.

85

 

Table 3.1. Composition of the test ﬁlms used in this study.

 

 

Test ﬁlm structures Thickness (mm) Manufacturer

PP/ 30 um nylon-6/PP 115 Rexham Inc.

PET 12 um /Al203 300A /LDPE 62.5 GL-AE Toppan Co.
PET 12 um/ SiOx 300A / LDPE 62.5 GL—AE Toppan Co.
Met-PET 12 um /30%VA EVA/LLDPE 50 Cello-Foil Pro. Inc.
PET/PVDC/nylon/HDPE/PP 102.5 Rexarn Inc.
PE/nylon/EVOH/PE 62.5 Cryovac
PE/nylon/PE 50 Cryovac
PET/PVDC/4%EVA 50 Cello-Foil Pro. Inc.

 

PP — Polypropylene

PET — Polyethylene terephthalate
Met-PET — Metallized polyethylene terephthalate
PE — Polyethylene

EVOH — Ethylene-vinyl alcohol

LLDPE — Linear low density polyethylene
HDPE — High density polyethylene

EVA — Ethylene-vinyl acetate

PVDC — Polyvinylidene chloride

SiOx -— Silicon oxide

A1203 — Aluminum oxide

86

 

3.3. RESULTS AND DISCUSSION

Untreated (control) and HPP-treated polymeric sample ﬁlms cut from the pouches
were analyzed for mechanical performance in both the machine and cross directions.
Machine direction (MD) refers to the parallel to which the ﬁlm is wound by the uptake
spool. In general, polymeric molecules are preferentially aligned in the MD as a result of
the applied stress during the spoolng and extrusion processes. Cross direction (CD) is the
orientation perpendicular to the machine direction and the polymeric chains tend to be
less aligned with respect to it. Since the results of the mechanical analyses of most
polymeric ﬁlms depend on whether the mechanical forces are applied in the MD or CD,
both directions were evaluated.

The tensile strength, percent elongation, and modulus of elasticity values, both in
MD and CD, for each material are shown in Figures 3.1 to 3. 6. These ﬁgures show little
difference between the results obtained for the controls (non HPP treated) and the ﬁlms
treated at 600 and 800 MPa for 5, 10, and 20 minutes at 45°C. The statistical analyses
shows that there were no signiﬁcant differences (p<0.01) between the controls and the
treated samples, both in the MD and CD, and within the treated samples at different time
and pressure conditions. Similar results were reported by Masuda et al. (1992). These
authors found no signiﬁcant changes in the tensile strength and percent elongation of
LLDPE/EVA/EVOH/EVA/LLDPE and PET/A1 Foil/PP structures before and after
pressure treatment at 400 MPa for 30 minutes at 60°C. Similarly, Mertens (1993)
reported no signiﬁcant effects caused by HPP on the tensile strength of PP/EVOH/PP,
OPP/PVOH/PE, PVDC-coated-OP/CPP and PET/Al/CPP ﬁlms treated at 400 MPa and

600 MPa for 10 min at 20°C. Also, no signiﬁcant changes were found in to the tensile

87

strength or percent elongation of pouches made of PP/PVDC/PP and high pressure
processed at 400 MPa.

The superﬁcial SEM micrographs for the control and treated ﬁlms except the
metallized-PET, at the 10-micrometer scale are shown in Figure 3. 7. The images show
the food-contact side of the ﬁlms. Processing values were 800 MPa and 20 minutes,
which represents the more severe conditions. Monolayer polypropylene ﬁlm was also
included for reference purposes since it is a homogeneous plastic ﬁlm with good
resilience, and therefore is able to absorb the hi gh-pressure impact without mechanical
deformation, as conﬁrmed by the images. Overall, no micro cracks or ﬁssures were
shown on any structure (Figure 3.7) that could weak the ﬁlms; this corroborates the
mechanical measurements. However, it appears that for PET/A12O3/LDPE ,
PET/SiOx/LDPE, and PET/PVDC EVA some superﬁcial small wrinkles were created
during HPP at the food-contact side of the ﬁlms. From the SEM images we cannot deduct
how these wrinkles were created, but again they did not affect the mechanical
performance.

Figure 3. 8 shows the micrographs for the controls, and the 600 and 800 MPa
treated metallized PET samples at lO-micrometer scale. These micrographs also conﬁrm
the absence of cracks or ﬁssures in the structures after the HPP treatments. However,
numerous and more pronounced wrinkles are seen on the food-contact layer.’ It appears
that the extent of these deformations tends to increase with increasing exposure times at
both 600 and 800 MPa pressures for the metallized PET. As with the other structures of
ﬁgure 3. 7, the presence of wrinkles does not affect the mechanical performance of this

ﬁlm.

88

 

Because coating layers are normally very thin compared with the thickness of the
polymeric layers (for example, 3 x 10'8m of coating versus 5 x 10’5 m for the polymer),
they do not signiﬁcantly contribute to the material’s mechanical strength. This means
that we cannot detect any damage in the barrier layer by the measuring the mechanical
properties, or by observing the external layer such as in SEM analysis. However one
practical consequence of the rupture in the continuity of a barrier layer in a multilayer
structure is an increase in the permeability to gases. Lambert et.a1. (2000) suggested that
only changes in barrier properties exceeding 25% are of industrial signiﬁcance. Using
this criterion, only metallized -PET would be unsuitable for high pressure processing at
conditions similar to those used in this study. In order to conﬁrm that metallized PET
ﬁlms could have been damaged at the metal barrier layer we carried out C-SAM studies.
C-SAM micrograph images of the metallized-PET were obtained for untreated and HPP
treated ﬁlm pouches (Figure 3.9). Mic'rographs consist of black and white images that
are composed of gray levels. The white areas correspond to the highest amplitude of
reﬂected acoustic signal, i.e. highly reﬂecting areas. In Figure 3.9, the white areas are
seen in the samples that were HPP treated, which indicate micro defects in the metallized
structure. According to C—SAM theory, the white areas are considered to be the result of
micro voids in the middle of the polymer ﬁlm. Differences between treated and control
ﬁlms are also well apparent in Figure 3.9. The heterogeneous acoustic reﬂectivity was
due to partly to an uneven surface. In these regions, the plastic structure could be
interpreted as ruptured in the continuity of the atomic aluminum coating deposited on the
PET layer. This unequivocally conﬁrms the weakening of the barrier property of the

metallized-PET structure while maintaining its mechanical performance. This study has

89

 

clearly demonstrated that C-SAM can be useful to identify the existence of defects and
properties, at the resolution of micro- and nanometer range. It is a very effective and
precise way to image defects in certain food packaging structures. Even though some of
structures have potential problems after high pressure treatment, ﬂexible multi-material
structures are the most suitable materials for prepackaged food products processed using
high pressure (Mertens, 1993; Mertens, 1995; Lambert et al. 2000). Packaging design is
still one of the important challenges for the high pressure processing industry (Knor,

l 996).

90

 

.8858 om 28 S .m cow Oomv we.
6258: A33 not“ EB @0988 283 eosooﬁc 0:388 3 25m came—a we AamEv 5%:on 26:3. .2“ SEE

  
 

 

 

 

 

 

00.. can
000. Avg oo 0% 9% @V 05
030. VOW/«V VGVAV Qaﬁc 009 “grow? ”74% %%$ @VQUQ 9%n? We”? TOAVV TIVAVVA. QVAP% 9%?009
V27 4V9 QsV 9W7 9% VV9 VVQ VA. Va. 9? avxv O/ O/ «V? «WV
8. A» A» V v r9 ﬁv/ 00».v 000. f6? TO? @w. 7 0% «%v V? ¢¢.
@POAt $0.08 Ind/(9 Awe/(0v %0/ %v0/ 9V)? 9%? %v0/ %v0/ 7 1%» %~¢OV @07 007 007
av 0 2b. +0. V V VV VV 9 «V «V 09 0 9 V~v vv/
. . o
2 I
_ - - E m m
. ,_.. om m
I r .. w
.... , on ow.
"1
m.
av W
n
3 .uum
9
.ﬂ.
. co m
w
m.
on .u
AZ: 58 ONE M
9
LL: EEO—i ,,. ow
mm: EE m. i
. 00

ea _ l
I :I II S 2:

91

lAtm. Press.
.5 min HPP

E10 min HPP
Z20 min HPP

 

100 -
90 -

MW 'uorroerrq $501319 mBuens ensue 1,

92

 

Figure 3.2. Tensile Strength (MPa) of ﬂexible Structure at cross direction before (controls) and after HPP treatment

at 45°C for 5, 10 and 20 minutes.

I :\.\\\\\\\\D\\\\.\\§\V
I t‘.§\\\\\\\\\\\\\\\\\V
l

‘.\\\\\\\\\\\\\\\\\\\\‘
| :EN\\\\\\\\,\\\\\\\\N\T

) x\\\\\\\\\\\\}\\\‘§
I

' \\\\\\\\\\\\\\\\
a
l :\\\\\\\\\\\\\‘
l . . ..
l
‘k\\\\\\\\\\\\‘
| ,.
l
T&\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\‘

r
I.

 

lAtm Press
.5 min HPP
.10 mm HPP
$20 min HPP

‘ T\\\\\\\\\\\\\\\\\\\\\\\V
l

Ek\\\\\\\\\\\\\\\\\\\\\‘
l . : .

 

 

.‘.k\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\‘

 

I:‘.‘.:\\\\\\\\\\\\\\\.\N\t\\§§.\\N\N\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\t\\\\\\\\\\\\\\\\\\\\\\\\\V

‘. \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\

 
 

\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\

 

 

800

L
‘N\\\\\\\\\\\\\V
‘.\\\\\\V\\\\\\\V
T I T I I I
O O O O O O O O
O O O O O O O
l\ \O If: V M N -‘

uorroerrq ourqoew re ureis moored

93

Figure 3.3. Percent Stain of ﬂexible structure at machine direction before (controls) and after HPP treatment at 45°C for 5,
10 and 20 minutes.

 

 

 

lAtm. Press.
.5 min HPP
510 min HPP

@20 min HPP

 
  

 

'

t .\\\\\\\\\\\\\\\\\\\\\x\\\s

l x\\\\\\\\\\\\\\\\\\\\\\\\‘

h

\

 

.'.
l

I ‘ k\\\\\\\\\‘

l \\\\\\\\\\‘

:\\\\\m

) .. ., .

I

I \\\\\\\\\\‘
I

I \x\\\\x\§\§\§x\\\\\\\s

: -\\\\\\\\\\\\\\\\\\\\\\

k\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\

m\\\\\\\\\\\\\\\

‘ .\\\\\\\\\\\\\\\\\\‘

 

700 —

600 —

500 —

400 r

300 t

200 -

O
O
_—

uorroenq 55013 112 urars moored

94

Figure 3.4. Percent Stain of ﬂexible structure at cross direction before (controls) and after HPP treatment at 45°C for 5,

10 and 20 minutes.

 

lAtm. Press.

900

.5 min HPP

  

gm min HPP
220 min HPP

I‘. x\\\\\\\\
.

 

 

 

 

800

O O
O O
l‘ \O

9m ‘uouqu

 

f k\\\\\\\\\\\\\\\\\\\
u.

 

\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\

O
C
If)

1

 

“' NWWWWW\

aurqaew In K110951213 jo snlnpow

\ \\\\\\\ \ \\\\k\\\\\\\\\\\b\

 

._ : nwmwmmm

/

 

 

 

I

 

“WV‘WWWW

 

:' k\\\\\\\\\\\\\\\\\\\\\\\\\§\\\‘\\\\\\\\\\\\\\\\\\\\\\V

      

 

\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\‘§\\‘

WWW}&\\\\\\\\\\\\\\\\\\\N‘

 

 

W

 

 

\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\}

 

_ k\\\\\\\.§§.\x\\\\\\\\\\\\\}\\\\\‘\\\\x\\\\\\\\\\§s

 

I

 

:‘ \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\§
. at.
\\\\\\\\\\\\\\&\\\\\\\\\\\\\\\\\\\\\\\\\\\‘

 

 

 

 

\\\\\N\\\\\\\\\\\\\\\V\\\\\\\\\\\\\\‘

o c O o o
o O o o
V M N -4

95

Figure 3.5. Modulus of Elasticity (MPa) of ﬂexible structure at machine direction before (controls) and after HPP treatment

at 45°C for 5, 10 and 20 rrrinutes.

 

.3356 cm use 2 .m c8 9.? a
Segue: .3: 5% was 32:53 283 gouache $90 on 830qu 0318c mo AmmEV 56:35 no 2:352 .c.m ocswE

e... 0e
0. we we
e. 5e... 2e. .eye.%ae¢e.. 2e. .5.... .5... are... eyes
17 vvev vvev m. o. a»??? a»??? Vow we? gee/r ﬁve/T 9% «WW.
O/T/v/ O/TO/ VAP% 47% %»7 7 O/TOAV #69 07 ﬁev. gav.
o

7
V o O 07 007
«a. we. a. «a. 5% 551 5% an 9%. ea» «ea we

              

 

 

 

  

2.. o
w
.... 2:
n W
. m 6
com m 9
.. S
a O
a r:
M 03 H
“u - be
a r ..s...
3
m 2:. «Au.
m w
. 3
m 2; w.
r. S
m d
.v 23 u.
3
= m...
.5255 SD 2:. .u
._._::_Eo_i M
B
.Z:Eemﬂ com
.395 .E.<I

 

 

 

PET/SiOx BOO/20

 

 

 

  

 

PE/EVOH Control

 

PE/EVOH BOO/20

 

 

PE/Nylon/PE Control

  

PET/ PVDC 800/20

PE/Nylon/PE 800120

 

PET/PVDC/EVA
Control _

 

 

 

PP Control

  

PP 800/20

 

 

 

800l20=800 MPa at 20 min

10pm

Figure 3. 7. Scanning electron micrographs of PP/ Nylon-6/ PP, PET / A1203/ LDPE, PET
/Si0x/ LDPE, PET/PVDC/Nylon/HDPE/PP, PP/EVOH/Nylon/PP,
PE/Nylon/PP, PET/PVDC/EVA and PP ﬁlms before (controls) and aﬁer HPP
treatment at 45°C for 5, 10 and 20 minutes.

 

 

Parameters ‘ Control 5 min 10 min , 2min
Met PET , ' , \
600 MPa

 

Met PET
800 MPa

 

 

 

 

Figure 3. 8. Scanning electron micrographs of metallized -PET pouches before (controls)
and after HPP treatment at 45°C for S, 10 and 20 minutes.

98

 

 

MET Metallized PET From food contact side From PET Side

 

 

 

Metallized PET From food contact side From PET side

ﬁg 5 Control Untreatele min 45 °C
-l —l

 

 

 

 

 

 

Treated 800 MPa 10 min 45 °C

 

Figure 9. Scanning acoustic micrograph of metallized -PET pouches before (controls)
and aﬁer HPP treatment at 800MPa and 45°C for 10 minutes.

99

 

3.4. CONCLUSION

From the results obtained in this study, it can be concluded that: 1) Metallized-
PET showed the most structural damage after high pressure processing. 2) Although
PET/A1203, PET/SiOx and PET/PVDC/EVA also showed some surface deformation, it
was to a lesser extent than what was seen in metallized-PET. 3) None of the tested
materials showed signiﬁcant changes in mechanical strength even though some showed
surface deformation. This research demonstrated that certain high barrier multilayer
ﬁlms can be affected by HPP. The magnitude of these changes depends on the type of
structure and the processing conditions. Even though some materials can be affected by
HPP, we found no evidence that these changes have a negative impact on the
performance of the materials. SEM showed that ﬁlms were not perforated or cracked but
showed wrinkles formation on selected ﬁlm surfaces. C-SAM analyses are useful tools in

the study of the internal structure of multilayer ﬂexible packaging materials.

100

 

3.5. REFERENCES

Aleman, G.D.; Ting, E.Y; Farkas, D.F.; Mordre, S.C; Hawes, A.C.O., and Torres, J.A.
1998. Comparison of static and step-pulsed ultra-high pressure on the microbial
stability of fresh cut pineapple. J Sci Food Agric 76: 383-388.

Ananth, V., Dickson, J.S., Olson, D.G., and Murano, EA. 1998. Shelf life extension,
safety and quality of fresh pork loin treated with high hydrostatic pressure. J Food
Prot 61(12): 1649-1656.

Barnes, R]. 1992. Effects of high-pressure sterilization on packaging. Food, Cosmetics
and Drug Packaging, Elsevier Science Publishers Ltd, England, pp 1-3.

Chen, C., Harte, B., Lai, C., Pestka, J., and Henyon, D. 1991. Assessment of package
integrity using a spry cabinet technique. J of Food Prot 54(8) 643-647.

Cherry, J .P. 1999. Improving the safety of fresh produce with antimicrobials. Food
Technol 53(11): 54-59.

Choudry, M.S., Lox, F., Buekens, A., and Decroly, P. 1998. Electron microscopic study
of the PVC bottle wall: The food-plastic interaction. Packaging Technology and
Science 11: 285-299.

Denys, S., and Hendrickx, ME. 1999. Measurement of the thermal conductivity of food
at high pressure. J of Food Sci 64(4): 709-713.

Hafsteinsson, H., Parker, K., Chivers, R., and Rizvi, S.S.H. 1989. Application of
ultrasonic waves to detect sealworrns in ﬁsh tissue. J of Food Sci 54(2): 244-247.

Karel, M. 2000. Tasks of food technologist in the 21St century. Food T echnol 5(6): 56-
64.

Knor, D. 1996. Advantages, opportunities and challenges of high hydrostatic pressure
application, in High Pressure Bioscience and Biotechnology, Ed by Hayashi R and
Balny C, Elsevier Science Publishers Ltd, England, pp 279-287.

Lambert, Y., Demazeau, G., Largeteau, S., Bouvier, J.M., Laborde-Croubit, S., and
Cabannes, M. 2000. Packaging for high-pressure treatments in the food industry.
Packaging Technology and Science 13: 63-71.

Liangji, X. 1999. Use of ozone to improve the safety of fresh fruits and vegetables. Food
Technol 53(10): 58-63.

MacDonald, L., and Schaschke, C]. 2000. Combined effect of high pressure, temperature
and holding time on polyphenoloxidase and peroxidase activity in banana (Musa
acuminate). J Sci Food Agric 80: 719-724.

101

 

Masuda, M., Saito, S., Iwanami, T., and Hirai, Y. 1992. Effect of hydrostatic pressure on
packaging materials for food, in High Pressure and Biotechnology, Ed by Balny C,
Hayashi R, Heremans K and Masson P, Montrougezlnserm/John Libbey Eurotex
Ltd, pp 545-548

Mertens, B. 1993. Packaging aspects of high- pressure food processing technology.
Packaging Technology and Science 6: 31-36.

Mertens, B. 1995. Hydrostatic pressure treatment of foodzequipment and processing, in
New Methods of Food Preservation, Ed by Gould G W, Blackie Academic and
Professional, New York, NY pp 135-158.

Ochiai, S., and Nakagawas, Y. 1992. Packaging for high pressure food processing, in
High Pressure and Biotechnology, Ed by Balny C, Hayashi R, Heremans K and
Masson P, Montrouge: Inserm/John Libbey Eurotex Ltd, pp 515-519.

Ozguler, A., Morris, S.A., and O’Brien, W.D. 1998. Ultrasonic imaging of micro-leaks
and seal contamination in ﬂexible food packages by the pulse-echo technique. J of
Food Sci 63 (4): 673-678.

Povey, M.J.W., and McClements, DJ. 1988. Ultrasonics in food engineering. Part I:
Introduction and experimental methods. J of Food Engng 8: 217-245.

Prestamo, G., and Arroyo, G. 1998. High hydrostatic pressure effects on vegetable
structure. J of Food Sci 63(5): 878-881.

Safvi, A.A., Meerbaum, H.J., Morris, S.A., Harper, CL, and O’Briend, W.D. 1997.
Acoustic Imaging of defects in flexible packages. J of Food Prot 60(3). 309-314.

SAS Institute, Inc, SAS/STAT user’s guide, version 6. Statistical Analysis Systems
Institute, Inc., Cary, NC (1990).

Sizer, CE, and Balasubramaniam, V.M. 1999. New intervention processes for minimally
processed juices. Food Technol 53(10): 64-67.

Sloan, EA. 1999. Top ten trends to watch and work on for the millennium. Food
Technol 53(8): 40-58.

Thayer, D.W., and Rajkowski, K.T. 1999. Development on irradiation of fresh fruits and
vegetables. Food T echnol 53(11): 62-65.

102

CHAPTER 4

The Effect of High-Pressure Food Processing on the Sorption Behavior

of Flexible Packaging Polymeric Films

ABSTRACT

The sorption behavior, or ﬂavor scalping, of selected, ﬂexible polymeric ﬁlms
ﬁlled with food simulant liquids based on ethanol and acetic acid aqueous solution was
evaluated aﬁer high pressure processing (HPP). Films used were single layer
polypropylene (PP), multilayer PE/nylon/EVOH/PE, and metallized PET/EVA/LLDPE.
The sorbate d-limonene, a component of the liquid simulant, was evaluated in both the
polymeric structures and the food simulants, at the HPP conditions (800 MPa, 10 min, 60
°C) and in an untreated control (latm, 60°C, 40°C) as a function of time. Analysis was
performed using a purge/trap and extraction technique and also gas chromatography
(GC). Results showed that d-limonene concentration, both in the polymers and in the
food simulants (in pouches) made of PP and PE/nylon/EVOH/PE was not signiﬁcantly
affected by HPP. However, the metallized PET/EVA/LLDPE showed a signiﬁcant
difference in d-limonene amount with respect to the control pouches. These results also
correlate with those obtained in previous studies. As expected, changes in temperature
signiﬁcantly affected the sorption behavior of all polymers. While PP and
PE/nylon/EVOH/PE films retained their d-limoenene amount, the metallized-PET clearly

did not.

103

4.1 INTRODUCTION

With increasing consumer demand for fresh-like and high quality foods with more
home style taste, there has been growing interest in development of new food processing
methods such as pulse electrical ﬁelds, irradiation, and high pressure processing (HPP).
Interest in HPP is steadily gaining important ground as a food preservation method that
maintains natural sensory and nutritional attributes (Gould, 2000). HPP can kill
microorganisms and inactivate enzymes by the physical action of very high pressures,
which are in the order of 100 to 800 MPa. In addition, HPP is a technique that can
produce uniform effects throughout the product, at low application temperature ranges
(0°C to 60 °C), causing effective preservation, and safe and comparatively easy operation
(F arkas and Hoover, 2000; Lambert et al., 1999). Today HPP is commercially used in the
Europe and Japan for processing products like fruit juice, guacamole paste, and tomato-
based salsa production (Neil, 1999). Liquid or solid foods can be high-pressure processed
with or without packaging (Farkas and Hoover, 2000). Flexible packaging structures allow
prepackaged foods to be processed by HPP, and therefore, prevents subsequent
recontamination by microorganisms. Flexible packaging structures are made from single
or multilayer, coated or uncoated, polymeric materials. Ideally, HPP should not affect to
any degree the integrity of the packaging structure.

Besides mechanical considerations, another important issue is that HPP may
affect plastic behavior regarding molecular mass transport between food and packaging
such as sorption and migration (Mitsui et al., 1992). This could affect the organoleptic

and nutritional quality attributes of the packaged product (Hernandez and Gavara, 1999;

104

Gavara and Hernandez, 1996). Three main types of interactions between food and
packaging materials are deﬁned i) permeation; ii) sorption and iii) migration (Olafsson
and Hildingsson, 1995). The effect of HPP on permeation has been described in chapter
(Mertens, 1993, Mertens, 1995).

The effect of HPP on the sorption behavior of plastics has not been sufﬁciently
researched, and is the focus of this work. Sorption refers to the uptake of volatile
components from the food product by polymeric packaging materials. Sorption, or ﬂavor
scalping, occurs readily in many types of foods, including juices, fruit-ﬂavored cereals,
and beverages. Sorption may eventually unbalance the product’s original ﬂavor proﬁle,
resulting in loss of food quality. This can lead to reduction of the shelf life of the
packaged food (Kwapon and Hotchkiss, 1987; Arora et al., 1991; Fayoux et al., 1997;
Gnanasekkharan and Floros, 1997). Sorption has been considered a main contributing
factor in degradation of ﬂavor or food quality during storage for some products (Nielsen
and Giacin, 1994; Fukamachi et al., 1996). Sorbed aromas may permeate through the
material, and evaporate outside the package, at a rate that depends both on their
diffusivity and on their solubility in the polymer (Lebosse, et al., 1997). Potentially, any
volatile food component could be lost by sorption to the packaging materials. Different
types of polymer materials have been shown to have various afﬁnities for aroma
compounds. Chemical composition (polarity), polymer morphology, temperature, and
pH of polymers are important factors that inﬂuence migration and sorption properties
(Nielsen et al., 1992; Nielsen et al., 1994; Leufven and Hermansson, 1994; Johansson and
Leufven, 1994).

Generally, the polyoleﬁns, i.e. LDPE, LLDPE and PP, absorb larger quantities of

105

aroma compounds than do polar polymers, such as PET and PA (Nielsen et al., 1992).
Matsui et al. (1992) also indicated that sorption greatly depends on the polarity of the

volatile compound.

The solubility parameter (6) was developed to describe the enthalpy of mixing of
simple liquids (nonpolar) but has been extended to polar solvents and polymers from
knowledge of the properties of the components (Grulke, 1999). For sorption, if the
polymer and sorbate have equivalent solubility parameters they should be mutually
soluble. In other words, substances with similar chemical structures should be quite likely
to dissolve in each other and exhibit a high propensity for sorbate/polymer interactions

(Hernandez and Giacin, 1998).

The solubility parameter, 5, of a substance measures the strength of attraction
between molecules within the material and is given by the square root of its molar
cohesive energy density. The value of 5 arises from the contribution of three inter-
molecular forces: dispersion (8d), polar (5p), and hydrogen bonding (6;): 52:82.1 +82p+62h.
Values of 6 can be obtained experimentally, or more commonly calculated by group
contribution methods. To determine whether a polymer favors the sorption of a particular
sorbate, the solubility parameter of both the polymer (8p) and compound (5L) need to be
compared. A large difference between the solubility parameters of the substances (when
(5;: - BL) is > 5 (J/cm3 )1/2) occur, lower solubility values are expected. However, good
solubility is obtained when (Sp-8L) is < 5 (J/cm3)”2.

The difference of solubility parameter values of the limonene and polymers were

calculated using the group contribution method (Sp-5L)=[(6d,p -8d, L)2 +(8p,p-8F,,L)2 +(5h,P

106

-8h,L)2]'/’ , where the subscripts d, p, and h refer to the type of molecular force as indicated
above, and P and L refers to polymer and d-limonene respectively (Grulke, 1999).
Calculating the difference in the solubility parameters can help to interpret sorption

results.

During HPP, an isostatic pressure is applied to the packaged product via a
pressure medium. This causes the product to compress uniformly up to 12 %, depending
on the ﬁnal pressure. The product returns to its initial volume after the pressure is

released. The compression forces also act on the polymer, reducing its volume.

HPP also increases the temperature of the food-package system according to
dt/dp=VT/pcp, where T is temperature, V is the thermal expansion coefﬁcient, and cp, is
the heat capacity. Compressed water will rise 3.0 C per 100 MPa.

Therefore, there is a combined effect of increasing temperature and decreasing
polymer volume during the HP treatment. These effects are reversible and the polymers
are expected to recover their initial condition after the treatment. In principle, the volume
decrease and temperature increase may affect the sorption behavior of the polymer during
HPP by decreasing the amount of sorbed. Once the pressure stops acting on the system, it
should be expected that polymers would revert to their initial state. While substantial
research has dealt with the speciﬁc effects of HPP on various food constituents, relatively
little is known about the effect on HPP on sorption behavior of ﬂexible food packaging
materials (Kubel et al., 1996; Imai et al., 1990).

Since better understanding is needed regarding sorption behavior of polymer

materials after HPP treatment, this study aimed to quantify change in the sorption

107

 

behavior of selected plastic structures when the food/package system is subjected to high
pressure. The objectives of this study were: a) to evaluate effect of HPP on the sorption
process in selected plastic structures; b) to determine the effect of temperature at 1 atm,
on sorption, and c) to predict the sorption behaviors of sorbate for polymers on the basis
of the afﬁnity concept by calculating the solubility parameter. For this purpose d-
limonene was selected as the sorbate and pouches made with the packaging structures
were ﬁlled with acid and low-acid food simulant liquids (FSL). D-limonene is a natural
terpene commonly found in citrus juices (Kutty et al., 1994). D-limonene can be easily
absorbed by many packaging materials because of its hydrophobicity (Mannheim et al.,
1987; Nielsen et al., 1992; Nielsen and Giacin, 1994). Its availability, prominence in
orange ﬂavor, and ease of analysis make it the most extensively studied compound with
respect to its sorption by polymers (F ayoux et al., 1997; Imai et al., 1990; Olafsson and

Hildingsson, 1995).

4.2 MATERIALS and METHODS
4.2.1 Materials

D-limonene (Clon) 98% pure (Aldrich Chemical Com. Milwaukee, WI) was
used as the sorbate. The food packaging ﬂexible structures (ﬁlms) selected were the
following (Table 4.1).

a) Single layer PP

b) PE/nylon/EVOH/PE

c) Metallized PET/EVA/LLDPE as an inorganic coated multilayer

108

Table 4.1. The composition of the test ﬁlms used in this study.

 

 

Test ﬁlm structures Thickness (um) Manufacturer
Met-PET 12 um /30%VA EVA/LLDPE 50 Cello-Foil Pro. Inc.
PE/nylon/EVOH/PE 62.5 Cryovac

PP (single layer for comparison) 25 Tredegar Inc.

 

PP — Polypropylene

PET - Polyethylene terephthalate

Met-PET — Metallized polyethylene terephthalate
PE — Polyethylene

EVOH — Ethylene-vinyl alcohol L
LLDPE — Linear low density polyethylene ' "
EVA — Ethylene-vinyl acetate

 

4.2.2. Equipment
4.2.2.1. High-pressure processor.

High-pressure processing was carried out using a pilot scale QFP-6 Tetra-Laval
Quinta] high-pressure processor (ABB Autoclave System, Columbus, OH). This
equipment contained a cylindrical 1 L -processing vessel with an internal diameter of 6.0
cm by 18.8 cmin height. It was designed for a maximum pressure of 890 MPa at an
operational temperature range of 5-700C. The processing temperature was maintained at
60 0C :2 0C for each test run. Three pouches were loaded into the pressure vessel that was

preheated to around 30 0C, then clamped within the hi gh-pressure chamber, and ﬁnally

pressurized for 10 min (holding time) up to 800 MPa at 60 0C, pressure processed. A

cooling system maintained the temperature of the chamber during the pressurization time.

109

The desired pressure was reached in 2.3 3:025 min. The high-pressure transmission ﬂuid
used in this equipment was Houghton-Safe 620-TY a glycol/water compound from
Houghton International (Valley Forge, PA).
4.2.2.2. Dynamic thermal stripper (DTS)/thermal desorption (TD)/gas
chromatograph (GC) system.
The extraction and quantiﬁcation of d-limonene from the ﬁlms was carried out using:
a) A dynamic thermal desorption unit Model 890 from Dynamic
Analytical Instrument, Inc., (Kelton, PA);
b) b) 6 mm OD x 4 mm ID. x 11.5 cm length Carbotrap® multi-bed
thermal desorption tubes (Supelco Inc., Bellefonte, PA).
c) Hewlett Packard 5890—A gas chromatograph equipped with a gas ﬂame

ionization detector (Avondale, PA, USA) and capillary column.

4.2.3. Methods

A ﬂow-sheet diagram indicating the main steps for preparing and analyzing the
samples is shown in Figure 4. 1.

Food simulants were selected to represent both acid and low-acid food simulant
liquids (FSL). Aqueous solutions of 165 ppm (165 mg/L) of d-limonene in either 10%
ethanol (Reagent HPLC grade, Sigma Chemical, St Louis MO) or 3% acetic acid
(Spectrum quality products, Inc, Gerdena CA) were prepared. The F SL were obtained by
mixing either 10% ethanol or 3% acetic acid with distilled water. The FSL was mixed
with d-limonene in a separatory funnel. After settling, the undissolved d-limonene upper

phase was separated from the F SL containing dissolved d-limonene.

110

Figure 4.1: Flow sheet diagram indicating main steps of general sample preparation.

 

 

 

 

 

 

 

 

Polymer Film

 

 

 

 

 

 

 

 

 

Liquid Organic Water Ethanol
Sorbate i j
Weigh Weigh

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Pouches
(
Food Simulant 10"“) cm
ﬂak Ethanol 10%
Water 90%
k
N
Separatory
funnel
J
l * a
. j
Un-disso|ved SOI‘ bate m fOOd f ,n h N COHU'O'
d-limonene simulant Fl pouc es Non-HPP
and seal
@ ' 1
High Pressure
Processing
Initial sorbate

concentration
in food simulant

 

 

 

 

 

[ Right after processing. ]

 

Liquid

J, Plastic

 

l

 

Liquids phase

 

 

 

 

$5

 

Sorbate
concentration in food
simulant aﬁer

a

 

Remove excess of
food simulant

 

 

 

l

 

 

 

 

 

 

 

 

 

 

 

 

 

Cut sample
0
Strip sorbate
in DTS
9 * V
Collect sorbate in Weight
trap tube polymer
0 V
CC analysis Calculate sorbate

 

 

 

111

concentration in
polymer structure

 

 

\ 1.0"." r.

 

The 10.0 x 10.0 cm pouches were fabricated from the ﬁlms, ﬁlled with F SL. Filled
pouches were heat-sealed with as little headspace as possible using a Sencorp heat-sealer
(Sencorp Systems, Inc., Hyannis MA). Samples were divided into two sets: one to be
kept at atmospheric pressure as control (23°C), and the other to be processed at high
pressure. Control pouches were exposed to atmospheric pressure (1 atm) at 60 °C for 10
min in an electric oven. In addition some control pouches were left at 40°C for 10 min.
For the treated sample, HPP was conducted at 800 MPa for 10 min at 60°C.

Sorbate levels in the ﬁlms were determined by DTS-TD and GC on aliquot strips
cut from the treated pouches. Three replicates of each pouch were analyzed for sorbate
content.

Two procedures were followed to describe the sorption behavior of d-limonene as
indicated in Figure 4.2. One procedure (A) was selected to evaluate whether the high
pressure would affect the unsteady state sorption process as compared to sorption at one
atmosphere. The second procedure (B) was for determining whether HP had any effect
on the sorption capacity of the ﬁlms once they were equilibrated with d-limonene at one
atmosphere. For procedure (A) the pouches were ﬁlled with FSL immediately before
HPP and then analyzed. In procedure (B) pouches were ﬁrst ﬁlled with FSL, then
allowed to equilibrate, and then HPP; analysis of pouches was performed before and after

HPP. Following HPP, pouches were kept at 23°C.

112

 

Figure 4.2: Diagram indicating the two procedures followed to evaluating the sorption
behavior.

a) Procedure A (Filled before HPP). Pouches werel) ﬁlled with F SL, 2) were pressure
treated and maintained at 23°C, and 3) aliquot of pouches and FSL were analyzed
according to the following schedule:

1) 18 pouches were ﬁlled

with FSL (10% ethanol and 18 with
3% acetic acid)

2) HPP

800 MPa
p 10 min 60°C
i Time in days

3) Analysis performed at: l d 2 (1 4d 6 d 12 d 20 days

 

 

 

 

 

b) Procedure B (At equlibrium HPP). Pouches were 1) ﬁlled with FSL and kept at 23°C
to equilibrate for several days, 2) pouches were pressure treated, and 3) aliquot of
pouches and FSL were analyzed according to the following schedule.

 

1) 9 pouches were ﬁlled with F SL
containing 10 % ethanol 2) HPP
and 9 pouches with 3% acetic acid 300 MP3

9 10 min
1 days 2 days 3 d. 60°|C
1 1 Time 1n days

3) Analysis performed at: 12 d 20 days

 

 

 

 

 

* days

113

4.2.3.1. Dynamic thermal stripping.

A Dynamic thermal stripper-thermal desorption (DTS-TD) unit was used to
extract the sorbate from the polymer sample. Polymer strips of about 20x25 mm were cut
from pouches and immediately transferred into the 20 ml sparging tube housed in the
20x20 x20 cm oven of the DTS instrument and connected to the sorption tubes containing
Carbotrap 300 multi-bed materials mounted outside the oven. The conditions used for the

thermal stripper unit and thermal desorption are summarized in Table 4.2.

Table 4.2. Thermal and ﬂow rate conditions used for the thermal stripper.

 

Preheat Purge Dry

 

He Flow rate, mL/min 50 100 50

Time, min 3 15 1
Block Oven Tube

Temperature °C 110 100 75

 

After stripping, the Carbotrap sorption tube containing the trapped sorbate was
transferred to the tube chamber of the thermal desorption unit. A transfer line connected
the thermal desorption unit to GC. Sorbate collected in the traps was thermally desorbed
from the carbotrap tube by heating into GC using the conditions shown in Table 4.3. A
stream of helium (7 mL/min, 275 kPa) quantitatively carried the sorbate directly into to
the GC for separation and detection. The quantities of sorbed compounds were obtained

the and used to evaluate the effect of high pressure on the sorption behavior.

114

Table 4.3. Conditions used for thermal desorption unit.

 

Tube desorption chamber temperature, (°C) 370
Valve compartment temperature, (°C) 250
Transfer line temperature, (°C) 250
Tube preparation chamber temperature, (°C) 350
Tube preparation chamber temperature, (°C) 350
Desorption time, min 5
Preparation time, min 20

 

4.2.3.2. Gas chromatography.

Quantiﬁcation of d-limonene was carried out on a Hewlett Packard 5890-A GC
equipped with gas ﬂame ionization detector and interfaced with a Hewlett-Packard 3395
integrator for separation and quantiﬁcation of the sorbate compound. The GC conditions
were as follows: He carrier gas at 7.0 ml/min, H2 at 40 ml/min, air at 400 ml/min, N2 at 30
ml/min, the initial oven temperature was 50°C for 2 min, and the temperature was raised
at a rate of 7 °C /min to 200 °C and kept forlO min.

The d-limonene concentration in the F SL, in g/L, was determined by direct

injection of 1.0 x 10 *5 L of solution into the GC._The amount of sorbate in the plastic was

C x A . . . . .
calculated as C = F—w——U , where C rs the concentratron rn microgram of d-lrmonene/ g

of polymer, AU is the GC area response, CF is the calibration factor, and W is the polymer

sample weight.

4.2.3.3. Determining d-limonene from plastic ﬁlm using a liquid extraction method.

Since the HPP equipment was housed 300 km from the lab where the analysis was

115

performed, a liquid-solid extraction procedure was used to extract the d-limonene sorbed
by the plastic ﬁlms immediately after HPP. The procedure was follows: Pouch samples
were cut into pieces of approximately 200 mg and dipped into 16 mL glass extraction
vials (Supelco Inc., Bellefonte, PA) containing 10 ml of solvent. The solvent was either
toluene for PP or a mixture of 70% toluene and 30% m-cresol for Met-PET and EVOH
based structures. The vials were tightly closed with screw caps lined with PTFE/silicone
septa (Supelco Inc., Bellefonte, PA) and kept for 24 hours at 40 °C in an oven for better
extraction conditions. Aliquots of the solutions were then injected into Carbotrap® tubes
and thermally desorbed directly into the GC port. The d-limonene concentration in the

CFxAUxVT

 

pouch material was determined by C = , where C is the concentration in :g

l X

of d-limonene/ g of polymer, AU is the GC area response, CF is the GC calibration factor,
W is the polymer sample weight, VT is total volume of solvent in the glass vials, and V1 is
injected volume of solvent in the Carbotrap® tube. Sampling times were different for
procedures (A) and (B). For procedure (A) the ﬁlm and FSL were evaluated right aﬁer
pressure treatment and atl, 2, 4, 6, 12, and 20 days for multilayer structures 1, 2, and 3
days for the single layer structure (Figure 4. 2). For procedure (B), the ﬁhn and FSL were
evaluated at after reaching equilibrium which are 4, 6, 12, and 20 days for multilayer
structure; 1, 2,and 3 for single layer structure (Figure 4. 2). Because multilayer structures
need longer time than single layer to reach equilibrium, sampling time for the single and

multilayer were different.

116

4.2.3.4. Statistical analysis

A completely randomized experimental design was applied to evaluate the effect
of high pressure processing on the sorption of d-limonene by polymers. The quantity of
d-limonene sorbed by the packaging structures was measured on samples HPP treated
and samples maintained at 1 atmosphere (referred to as controls). Statistical analysis of
data was carried out by using the Statistical Analysis Systems PROC MIXED procedure
(SAS Institute, Inc., NC.(32) statistical software. Least Square Mean (LSMEAN S)
differences adjusted by the Tukey adjustment factor were also used to determine

differences between factor levels.

4.3. RESULTS AND DISCUSSION
The quantity of sorbed -d-limonene both in polymer structures and in the food

simulants were determined for each structure as according to Figure 4. 2.

4.3.1. Polypropylene (PP)

Figure 4.3 compares the sorption of d-limonene by PP structure in contact with d-
limonene in 10% ethanol at 800 MPa, for 10 min at 60 °C. Figure 4.2 compares the
sorption of d-limonene by PP in contact with 3% acetic acid at 800 MPa, for 10 min at 60
°C. For comparison of temperature effect on sorption we also compared 40 °C control
(latm). These ﬁgures show a rapid increase in the sorbed amount of d-limonene to reach
a maximum value that tends to approach a pseudo equilibrium point. After that there is a
decrease in concentration created by loss of d limonene by permeation with simultaneous

decrease in concentration in the liquid phase. The sorbed amount of d limonene was not

117

signiﬁcantly (P<0.01) affected by pressure treatment. D limonene shows a rapid sorption
increase (2228 3:51) in about 6 hours to reach a maximum value of 2300 d: 49 micrograms
per gram PP in 10 % ethanol and about 800:1:36 micrograms per gram of PP in 3 % acetic
acid (Figure 4.3 and Figure 4.4).

Losses of d-limonene in the food simulant liquid are shown in Figure 4.5 and 4.6.
As shown, the liquids lose 0.047 $0.004 g/L for ethanol and 0.003i0.0005 g/L for 3%
acetic acid) in about 24 hours due to permeability of the d-limonene through the ﬁlm.
Similar behavior in terms of sorption of limonene was shown in both HP processed and
non-HPP ﬁlms. No signiﬁcant (p<0.01) differences were found.

Absorption of D-limonene in an acetic acid food simulant was much lower than

an ethanol food simulant.

118

 

 

2500 .,

l

l
2000 l.

l

 

 

 

 

 

a
n.
% 1500 l
c ..
0 l
C
3 l'>
f 1000 1
O = I"
3‘ .
500 L
o ' "‘ ‘—’“ T'_—‘-—' ’—T— "_’— ' _“— ' '_—_ '— '__ _—T——— l” ‘——"_ "" I
0 10 20 3O 40 50 60 70 80 90 100
Time. hours '
I" demo; '60 °c _ fooaoa‘Zo‘BE—“i ' ”iv—roog‘ciure 5 'f _0 Procedure '31 5

 

 

Figure 4.3: Concentration of d-limonene in PP ﬁlm contacting 10% ethanol FSL treated

at 800 MPa and 60 °C according to procedures A (Filled before HPP) and B
(At equlibrium HPP).

1000 7
900 J
800-1
700 -
600 ~
500 .
400 «
300 -
200 ,
100 -

0 l.____...____ .-~—

 

pg of limonene/g PP

 

 

 

 

T L . ..,-- . _ﬁ _ __*‘_,-. __

0 10 20 30 40 50 60 70 80 90 100
Time. hours
:Edntrél'éd‘ci .Lééhﬁ4075“.:i":rocedurgo Cajjrécegure 8‘

 

 

 

Figure 4.4: Concentration of d-limonene in PP ﬁlm contacting with 3% acetic acid FSL

treated at 800 MPa and 60 °C according to procedures A (Filled before HPP)
and B (At equlibrium HPP).

119

 

d-Iimonene concantration g/L

 

 

 

 

o i- , _ .-# ,7--_._---._- 2i . -_-.
0 0.5 1 1.5 2 2.5 3
Time, days
‘ ——Control 60 °C ~ Control 40 °C x Procedure A 0 Procedure BJ

 

 

 

 

Figure 4.5: Concentration of d-limonene in FSL (10% ethanol) in PP ﬁlm treated at 800

d-limonene concantration gIL

MPa and 60 °C according to procedures A (Filled before HPP) and B (At
equlibrium HPP).

0.02 ‘
0.018 “t:

0.016 1

0.014 '
0.012
0.01

 

0 w—H- r — -- + -~~ -——~——+ _——-————- +——~-— *-
0 0.5 1 1.5 2 2.5
Time, day

l' —W "@330?ch WQWCanrr—QZW'EWWYW Wooedure A ___g_ProcedureB i

 

 

 

 

 

 

Figure 4.6: Concentration of d-limonene in FSL (3 % acetic acid) in PP ﬁlm FSL treated

at 800 MPa and 60 °C according to procedures (Filled before HPP) and B (At
equlibrium HPP).

120

 

 

 

4.3.2. PE/nylon/EVOH/PE

A similar pattern was observed for the PE/nylon/EVOH/PE structure. Figure 4.7,
4.8, 4.9 and 4.10 summarize the results obtained with this ﬁlm. The amount of d-
limonene concentration was not signiﬁcantly (P<0.01) affected by HPP. D-limonene
values are the same before and after treatment (800 MPa, 10 min, 60 C). D-Limonene
concentration increases slowly for EVOH, and in about 2 days reaches at with a value of
600:1:15 micrograms per gram EVOH in 10% ethanol and about 5012.5 micrograms per
gram of EVOH in 3% acetic acid (Figure 4.7 and 4.8). Losses of d limonene are shown
in Figure 4.9 and 4.10. The liquid d-limonene contents about 0.01 8:1:0.0012 g/L in about
one week for the 10% ethanol (Figure 4.9). D-Limonene concentration was about
0.017i0.001 g/L in about one week for the 3% acetic acid solution (Figure 4.10). The
liquid d-limonene concentrations were lost half of its-d limonene in about one week. The
amount of d limonene (0.014i0.0015 g/L for 10% ethanol and 0.013:t0.0012 g/L for the
acetic acid) was the same before and after HPP after 20 days (Figure 4. 9 and 4. 10). No
signiﬁcant differences (p<0.01) were found between the HPP treated and non-treated
pouches.

As expected, pouches made of the EVOH multilayer structure took a much longer
time to lose the limonene compared to pouches of single layer PP.

Since single layer structures may not be able to meet all the demands for many

packaged products, combinations of polymers are used as laminates, to achieve the

intended shelf life.

121

 

pg of limonene/g EVOH

 

 

Li—W;Wc§rjy9I—eo °CW —-W~ control 40 °C at _' ProcedureWA-HW— 6M”— WEB?

 

 

Figure 4.7: Concentration of d-limonene in PE/nylon/EVOH/PE ﬁlm contacting with
10% ethanol FSL treated at 800 MPa and 60 °C according to procedures A
(Filled before HPP) and B (At equlibrium HPP).

100 7
90 1

pg of limonene/g EVOH

 

 

0 2 4 6 8 10 12 14 16 18 20
Time, day

W *T‘aaror 60 °c

9.2. . . 27*

 

--W-WContr0l 40 '0 )K _ Procedure A _ I 0 Procedure 8

 

 

Figure 4.8: Concentration of d-limonene in PE/nylon/EVOH/PE ﬁlm contacting with 3%
acetic acid FSL treated at 800 MPa and 60 °C according to procedures A
(Filled before HPP) and B (At equlibrium HPP).

122

(1035

(103

 

 

 

 

 

_J
a
5 0.0251
'3
g 002 “
C -.
a ' - _gg
o 0.015. 2;
C
0
S
g 0.011
'6
0.005 -
o. . -_-.--iV---- . . . ._2’--_-... -_.-.. .. ._
o 2 4 e 8 10 12 14 16 18 20
Time.days
Control 60 °c Control 40 °c ’ _x Procedure A_ _ <>__ ProcedureBE

Figure 4.9: Concentration of d-limonene in F SL (10% ethanol) in PE/nylon/EVOH/PE
ﬁlm treated at 800 MPa and 60 °C according to procedures A (Filled before
HPP) and B (At equlibrium HPP).

0.035

0.03 E

0.025

0.02 ~

0.015: W WW W WWL“"“‘“*~-~—--‘{

 

 

0.01 -

d-limonene concantration g/L

0.005

0 2 4 6 8 10 12 14 16 18 20
Time. days

 

C’ontrolW4’0 °c x ProcedureA ’ ‘6 W Procedure—B“;

 

con}... 60 °c W

 

 

Figure 4.10:Concentration of d-limonene in FSL (3% acetic acid) in PE/nylon/EVOH/PE
ﬁhn treated at 800 MPa and 60 °C according to procedures A (Filled before
HPP) and B (At equlibrium HPP).

123

4.3.3. Met-PET 12 um /30%VA EVA/LLDPE (coated multilayer structure)

Figures 4.11, 4.12, 4.13 and 4.14 summarize the results for the met-PET polymer
structure for both the polymer and food simulant. The d-limonene concentrations in the
treated pouches were signiﬁcantly lower than in the non-HPP ones. The amount of d-
limonene continuously decreased during the 20-day period of observation. The control
met-PET showed a relatively slow sorption process reaching a maximum in about 4 days
at a value of 1300 i55 micrograms per gram of polymer in 10% ethanol and about
85i7.5 micrograms per gram of polymer in 3% acetic acid (Figure 4. 11 and 4. 12,
respectively). It can be seen that d-limonene in the HPP treated met-PET was
signiﬁcantly (p<0.01) different from the non-HPP treated met—PET. The amount of d-
limonene in 10% ethanol FSL was 0002622000058 g/L limonene for right after HPP
(procedure A; Figures 4.2) at 4 days (Figure 4.13). The amount of d-limonene in 3%
acetic acid FSL was 0.00339i0.000486 g/L for HPP at equlibrium (procedure B; Figure
4.2) at 4 days (Figure 4.14). Similarly, the result of PROC MIXED SAS analysis among
overall (20 days storage time) the d limonene concentration of FSL in the HPP treated
met-PET for the 10% ethanol and 3% acetic acid solution are signiﬁcantly (P<0.01)
different from the non HPP treated met-PET (Figure 4.13 and 4.14). The values of the d-
limonene in the food simulant were found to be signiﬁcantly (p<0.01) lower in HPP
processed pouches as compared to the non-HPP pouches, both in 10% ethanol and 3%
acetic acid (Figure 4.13 and 4.14, respectively). Sorption-permeation behavior of the

met-PET was profoundly affected by the HPP treatment.

124

1600 1

1400 4

 

1200 1

 

400 -.

pg of limonene/g MET-PET

 

 

 

0 2 4 6 8 1O 12 14 16 18 20
Time. days
lh—Control 60_°C ’77.: Control 40 °C 2; - Procedure A“ Q Procedure 8 j

 

Figure 4.11: Concentration of d-limonene in Met-PET/EVA/LLDPE ﬁlm contacting with
10% ethanol FSL treated at 800 MPa and 60 °C according to procedures
(Filled before HPP) and B (At equlibrium HPP).

 

pg of limonene/g MET-PET

 

o .._W. __. ._. ..__ __ ._ ..2._ . ___._ _ _. . _ .__ “..._ ..._. ._._ _.._ _a

0 2 4 6 8 10 12 14 16 18 20
Time, day

 

Control 60 °C _- ~— QTControl 40 °C X Procedurefx- 0‘ - __l—Drocedure 8

 

 

 

l
L__ 2....

 

 

Figure 4.12: Concentration of d-limonene in Met-PET/ EVA/LLDPE ﬁlm contacting
with 3 % A.A F SL treated at 800 MPa and 60 °C according to procedures A
(Filled before HPP) and B (At equlibrium HPP).

125

d-Iimonene concantration g/L

 

 

 

 

0 2 4 6 8 10 12 14 16 18 20
2,. _2, _ __g 1 {_vTime.day_s ”___ 7_;__ __ ___m_ _
’ Control 60 °C ~- , ~ Control 40 “C X Procedure A 0 Procedure B l

 

Figure 4.13: Concentration of d-limonene in 10 % ethanol FSL in Met-PET/EVA/LLDPE

d-limonene concantration glL

ﬁlm treated at 800 MPa and 60 °C according to procedures A (Filled before
HPP) and B (At equlibrium HPP).

0.025 ~

I
0.02 I
1"

0.015

 

 

 

 

 

 

0.005
~ i 5 h ..._ __ ___ m; A _ v —
8 a:
0 I "*“‘ H‘— . r I — I 1 " "' r T— ““ "
0 2 4 6 8 1 0 1 2 14 1 6 18 20
Time. days
Contro'GQLQinj 0 (35193331317010. 8100135095 _°__:P_r:9*:9_qt€_9j

 

Figure 4.14: Concentration of d-limonene in FSL (3% acetic acid) in Met-PET 12 pm

/30% VA EVA/LLDPE ﬁlm treated at 800 MPa and 60 °C according to
procedures A (Filled before HPP) and B (At equlibrium HPP).

126

 

For the PP and EVOH structures, the d-limonene content of pressure-processed
pouches was similar to non-treated ones. However, for the met-PET this was not the case.
D—limonene concentration decreased in the polymer with time after reaching a maximum
value, due to permeation. The pH of the F SL was found to inﬂuence the amounts of
aroma component sorbed in the polymer. The equlibrium values achieved for 10%
ethanol were 2300i49 microgram/ g for PP, 600i15 microgram/g for EVOH and 1300
$55 microgram/g. for met-PET. The equlibrium values achieved for 3% acetic acid was
800:t36 microgram/g for PP, 5012.5 microgram/g for EVOH and 85i7.5 microgram/ g for
met-PET. These results were in agreement with Leufven and Hermansson.

Process temperature was shown to have an impact on the degree of sorption of d-
limonene by the polymer. As expected, signiﬁcantly (P<0.01) lower amounts of d-
limonene were sorbed at higher temperature (6OEC) as compared to the lower
temperature (4OEC) for all structures (Figures 4. 3- 4. 14). Also, temperature accelerated
the sorption process and the time to reach the maximum was shorter at higher
temperature (60C). This is in agreement with Nielsen et al. (1992) and (1994); Fayoux et
al. (1997). The reason for the increasing values at higher temperature might be due to
the greater mobility of molecules, or that the polymer may have been affected in some

way, such as swelling.

Temperature rise due to compression heating depends on the pressure, product
compressibility, and initial temperature. The pressure media also great inﬂuences the
apparent product temperature rise in a process vessel. Water (3°C per 100 MPa) is the

lowest compression heating increment during the pressure treatment. Change in product

127

 

temperature as a result of compression heating and subsequent heat transfer should be
considered during HPP. Foods are composed mostly of water and water has very low
compressibility. There is no heat transfer during HPP. However, depending on the food,
a slight temperature change may occur with compression. This is reversed during
decompression. The effect of changing pressure has signiﬁcant effects on the volume
temperature relationship due to the compressible nature of the polymer. An increase in
pressure decreases the speciﬁc volume at given temperature. It is remarkable that the
compression response of the polymers is so similar. This may occur if molecules are very
tightly bound so that displacements around the minimum are equally difﬁcult in
compression or dilation. For organic compounds, with weak attractive van der Waals
forces, it was expected that a much less symmetric internal energy (compression more
difﬁcult than dilation) would be found.

In Table 4.4 are summarized the a values of the limonene compounds and contact
polymers used in this study. The solubility behavior of an unknown substance often gives
us a clue to its identiﬁcation, and the change in solubility of a known material can
provide essential information about its aging characteristics. The solubility parameters of
the d-limonene and polymer indicate chemical similarity between the polymer and d-
limonene (Table 4.4). The smaller the differences between the a values of two
substances the greater the solubility (Grulke, 1999). Consequently, a comparison of 6
values of a polymer and an aroma compound gives an indication of their solubility
behavior. Differences of solubility parameters values of d-limonene and PP, PE and

LDPE (d-limonene-polymer) were lower than 5 (66 =0.5 (J/cm3)“2 <5 (J/cm3)."2 ).

128

 

Therefore a high degree of compatibility was expected between limonene and PP, PE and
LDPE. Since the solubility parameters are similar, completely miscibility is expected to

occur. The difference of solubility parameters values between d-limonene and PET

 

(12.8), Nylon (13.4), EVA (15.39) and EVOH (5.36), indicating that all of the limonene-
the polymer (Sp-8L) greater than 5 (J/cm3 )1/2 (66 =0.5 (J/cm3)“2 >5 (J/cm3 )1/2 poor

solubility is expected). Therefore, a low degree of compatibility was expected between |_
limonene and PET, Nylon, EVA and EVOH. The solubility parameter (a) is a useful

measure to qualitatively estimate the solubility of a solvent in a polymer, and is a good

 

indicator of the chemical compatibility between a sorbate and a polymer. 3"

D-limonene, which is a non-polar compound and, has a small dipole moment, had
the greatest afﬁnity for the plastic phases. As seen from these results there were major
differences between the amounts of d- limonene absorbed by the different polymers.
Generally poyoleﬁns, i.e. PP, absorb larger quantities of aroma than more polar

polymers, such as PET (Nielsen et al., 1992).

Table 4.4. The solubility parameters, 5 (J/cm3) and Sp-SL

 

 

Substance 8a (J/cm3) 8d 6,, 8.. esp-8L
(J/cm3)“2 (J/cm3)“2 J/cm3)“2 (J/cm3)”2
Limonene 16.84 0 O 0
PP 17.28 17.28 0 0 0.19
PE 17.31 17.31 0 0 0.22
LLDPE 17.31 17.31 0 0 0.22
PET 22 17.9 7.3 10.5 12.8
Nylon 22.87 18.62 5.11 12.28 13.4
EVA 25.66 20.93 11.27 9.66 15.39
EVOH 22.2 —- - - 5.36 *
Water 48 13.3 31.3 34.2 45.2

 

Source of 8, 5d, 8,, 8., were Grulke, 1999.Table 10. * Calculated based on solubility parameters

129

_f-a 1.170

 

 

1 6.3?1

8.183

8.598

 

 

STRRT

Figure 4.15. Coming up time for d-limonene using GC.

130

9.165

 

4.4. CONCLUSION
When pouches made of the selected polymers (PP, EVOH, metallized-PET) are

submitted to a pressure treatment at 800 MPa for 10 min; no signiﬁcant changes in the
sorption behavior are observed compared to unprocessed structures from in PP and
EVOH. D-limonene concentration in both F SL 10% ethanol and F SL 3% acetic acid were
not signiﬁcantly changed aﬁer high pressure treatment. On the contrary, Metallized-PET
was signiﬁcantly (P<0.01) affected by HPP. D-limonene amount in pressure treated both
Metallized-PET and also FSL (10% ethanol and 3% acetic acid) were signiﬁcantly lower
than non-high pressure treated ones .

In terms of d-limonene retention, EVOH appeared to be the best of the three
polymers. Sorption by MET-PET and EVOH was signiﬁcantly less than for PP.
Furthermore, sorption of d-limonene amount was lower in the multilayer structure.
Temperature affected the amount of sorbed d-limonene and the time it took to reach the
maximum value. Sorption is also affected by the pH of the FLS. Using acetic acid to
lower the pH altered the solubility of d-limonene in the polymer. Factors that affected
absorbed amount of d-limonene depended on polarity and solubility properties of the
polymers and on the type of food simulant. Solubility parameters can be used to predict
sorption behavior of plastic and polymer-solvent interaction. It may also possible to
estimate the order of solubility behavior based on compression of 6 values of a polymer
and an aroma compound.

The above d-limoenene values indicate that existing single layer and multilayer

plastic packaging structures can be used in combination with HPP.

131

 

4.5. REFERENCES

Arora, D. K., Hansen, A. P., Armagost, M. S. 1991. Sorption of ﬂavor compounds by
low density polyethylene ﬁlm. Journal of Food science. 56(5): 1421-1423.

Farkas, D and Hoover, GD. 2000. Journal of Food Science sublement. High pressure
processing. 65 (4) 47-64.

Fayoux, C.S., Seuvre, A.M., Voilley, J. 1997. Aroma transfers in and through plastic
packaging: Orange juice and d-limonene. A Review. Part 2: Overall sorption

mechanisms and parameters-a literature survey. Packaging Technology and
Science. 10:145-160.

F ukamachi, M., Matsui, T., Hwang, Y.H., Shimoda, M., and Osajima, Y. 1996. Sorption
behavior of ﬂavor compounds into packaging ﬁlms ﬁ'om ethanol solution. J Agri.
Food Chem. 44: 2810—2813.

Gavara, R., Hernandez, R.J., Giacin, J. 1996. Methods to determine partition coefﬁcient
of organic compounds in water/polystyrene systems. Journal of Food Science.
61:947-952.

Grulke, EA. 1999. Solubility parameter values. P 675-713. in Brandrup J. and Irnmergut
E.H., and EA. Grulke (ed)., Polymer Handbook.

Gnanasekharan, V., Floros, J .D. 1997. Migration and sorption phenomena in packaged
foods. Critical Reviews in Food Science and Nutrition. 37(6) 519-559.

Gould, G.W. 2000. Emerging technologies in food preservation and processing in the
last 40 years. p: 1-11.in G. Barbosa-Canovas and G. W. Gould (ed.), Innovations
in Food Processing. Tecchnomic Pub. Lanscaster Basel.

Hernandez, R.J.; Giacin, J .R. 1998. Factors Affecting Permeation, Sorption, and
Migration Processes in Package-Product Systems. In: Quality Preservation in
Food Storage and Distribution, Chapter 10. Edited by T. Taub and R. Singh. CRC
Press, Boca Raton, Florida.

Hernandez, R.J., Gavara, R. 1999. Plastic packaging: methods for studying mass transfer
interactions. Pira International, Leatherhead, United Kingdom. p.5-31.

Imai, T., Harte, B.R., Giaicin, J .R. 1990. Partition distribution of aroma volatile from

orange juice into selected polymeric sealant ﬁlms. Journal of Food Science. 55
(1): 158-161.

Johanson, F. and Leuven, A. 1994. Food packaging polymer ﬁlms as aroma vapor
barriers at different relative humilities. Journal of Food Science. 59 (6): 1328-

132

 

1331.

Kwapong, O.Y., Hotchkiss, J .H. 1987. Comparative sorption of aroma compounds by
polyethylene and ionomer food-contact plastics. Journal of Food Science. 52 (3):
761-763.

Kubel, J ., Ludwig, H., Marx, H., and Tauscher, B. 1996. Diffusion of aroma compounds
into packaging ﬁlms under high pressure. Packaging Technology and Scinece. 9:
143-152.

Kutty, V., Braddock, J ., and Sadler, GD. 1994. Oxidation of d-limonene in presence of
low density polyethylene. Journal of Food Science. 59 (2) 402-405.

Lambert, Y., Demazeau, G., Largeteau, A., and Bouvier, J .M. 1999. Changes in aromatic
volatile composition of strawberry aﬁer high pressure treatment. Food Chemistry.
67: 7-16.

Lebosse, R., Ducruet, V., Feigenbaum, A. 1997. Interactions between reactive aroma
compounds from model citrus juice with polypropylene packaging ﬁlms. J. Agric.
Food Chem. 45, 2836-2842.

Leufven, A. and Hermansson, C. 1994. The sorption of aroma components from tomato
juice by food-contact polymers. J. Sci Food Agric. 64: 101-105.

Mannheim, C.H., Miltz, J ., Letzter, A. 1987. Interaction between polyethylene laminated
cartons and aseptic packed citrus juices. Journal of Food Science. 52 :3 73 7-740.

Matsui, T., Nagashima, K., Fukamachi, M., Shimoda, M., Osajima, Y. 1992. Application
of solubility parameter in estimating the sorption behavior of ﬂavor into
packaging ﬁhn. Journal of Agricultural Food Chem. 40:1902-1905.

Mertens, B. 1995. Hydrostatic pressure treatment of food:equipment and processing,
p.135-158. Gould, G. W (ed.). In New Methods

Mertens, B. 1993. Packaging aspects of high pressure food processing technology.
Packaging Technology and Science. 63:31-36.

Neil, HM. 1999. High pressure pasteurization of juice. Food Technol. 53(4): 86-90.

Nielsen, T.J., and Giacin, J .R. 1994. The Sorption of limonene/ethyl acetate binary vapor
mixtures by a biaxially oriented polypropylene ﬁlm. Packaging Technology and
Science 7:247-258.

Nielsen, T.,Jagerstad, M. I., Oste, RE. 1994. Study of factors affecting the absorption of
aroma compounds into low-density polyethylene. J. Sci Food Agric. 60: 377-381.

133

Nielsen, T., Jagerstad, M.I., Oste, R.E., Wesslen, 3.0. 1992. Comparative absortion of
low molecular aroma compounds into commonly used food packaging polymer
ﬁlms. Journal of Food Science. 57(2) 490-493.

Olafsson, G., and Hildingsson, A. 1995. Sorption of fatty acids into low density
polyetylene and its effect on adhesion with aluminum foil in laminated packaging
materail. J. Agri. Food Chem. 43: 306-312.

SAS. 1990. Institute, Inc, SAS/STAT user’s guide, version 6. Statistical Analysis
Systems Institute, Inc., Cary, NC.

134

5'1."- ‘ .

 

 

Chapter 5

Conclusion and Future Work

The permeability, mechanical behavior by measuring the tensile properties,
and use of SEM and C-SAM techniques and sorption behavior were studied. Results from
these studies showed that permeance of the most of the multilayer structures tested were
unaffected and suitable to high pressure treatment, even though some of them were
statistically signiﬁcant. However, the metallized PET inorganic coated multilayer was
most severely affected by the high pressure processing. Higher (800 MPa) pressure and
longer processing times (20 min) seem to have a more pronounced effect on permeance
values when we compare the change lower (600 MPa) pressure and shorter exposure
times (5 min). The water vapor permeance were more than 100% higher in most cases
and had more changes when we compare to oxygen and carbon dioxide.

Images obtained using SEM and C-SAM conﬁrm that metallized-PET showed
the most structural damage after high pressure processing. SEM showed mettalized-PET
had numerous folds and wrinkle formation on the ﬁlm surfaces. C-SAM analyses showed
that delamination occurred in random locations at the interlayer of met-PET.

None of the tested materials showed signiﬁcant changes in mechanical
strength even though some showed surface deformation.

Sorption behavior was tested to determine sorbate amount (d-limonene) in the
polymer and in the food simulant liquid. D-limonene concentration in both PP and
PE/Nylon/EVOH/PE was not signiﬁcantly changed after high pressure treatment. D-

limonene concentration in both F SL 10% ethanol and F SL 3% acetic acid were not

135

 

 

 

signiﬁcantly changed after high pressure treatment. On the contrary, d-limonene
concentration in pressure treated metallized-PET and also in FSL (10% ethanol and 3%
acetic acid) was signiﬁcantly lower than non-high pressure treated.

This research demonstrated that certain high barrier multilayer ﬁlms can be
affected by HPP. The magnitude of these changes depends on the type of polymer
structure and the processing conditions. Even though metallized-PET can be affected by
HPP, we found that the rest of the structures tested not have any negative impact on the
properties of the materials. The materials (except metallized-MET) are suitable for batch
high pressure processed food packaging.

Understanding of changes in inorganic coated multilayer structures such as
metallized-PET is crucial. Although detailed research has been done in this study in terms
of the effect of HPP on plastic structures much remains to be done to conduct additional
modeling research, using different metallized inorganic multilayer structures.
Investigating the inﬂuence of pressure on permeability, mechanical and mass transport
properties using proper experimental design (collection of data at different pressures and
control of temperature) on different metallized inorganic coated structure can be helpful.

It is also recommended that further studies on bottles and other ﬂexible
containers be carried with high-pressure treatment.

In this way, critical process factors can be evaluated for polymer structures.
Also, more stability studies are needed to identify the main diminishing plastic properties,
which affect food quality and safety during storage of pressure-processed foods.

There is no doubt that HPP has a promising future as a prepackaged

preservation method. Research is particularly needed to set critical limits of the process

136

 

 

and extent to which this might ensure appropriate treatment of prepackaged food
products. The possible commercialization of HPP also depends on its economic viability.
Therefore, detailed economic analyses of HPP need to be done by comparing process

costs with commercial methods.

137

 

Appendix A

Statistical analysis
The analysis of variance (AN OVA) was performed using LSM-PROC GLM

in SAS program.

 

 

 

138

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Kmo Sod oSo 3+ N_o_.o mmmé mmmo Rod emzoow Hum 62
m _omo oo.v omoﬁo mod sumo wood mmmo _moN EZooo Ema 82
omoo 3v; _mmoo Nov; NVmoo mic.— omoo Sm; mmEoow 93%?me
omoo mil ovooo one; Smoo :1 omoo Sm; mmEooo mEmONZFmE
m goo oomg Nohoo mom; wmwoo 9:: mod mum; mmzoow xgmhtmm
mowoo mow; mwoo Nov; vwoo mmv; ovoo mum; meooo 55>me
ommo 31m 2 _.o Row 2 _o mo_.m _wmo Nome nmEoow mags—Eton
oomo Ema oomo mmmo Vmoo homo Smo mmwé mmEooo mags—33m
moo EmNN mo.m momm oo.m mdmm wm.m momm $28» no
om.m Nomm who 5. EN 2mm ZZN mm.m momm £388 on
Ewmo ohmo oooﬁo ammo oovo ommo woomo oomd mLZoow mEcoREmm
vow—o mmmo _mwoo oomd Nwovo mnmd woomo oom.o HEZooo mmEoREm—m
owoo mmmd mwoo mw_.m mooo 3:” wood God 3988 mn<<>m>~mm
owoo oomd mooo _o_.m omoo wood wood _oo.m amzooo mE<>umE
ma:
good 30; onnoo woo; ammo moo; m Sod 34o; mmEoow EO>mEoEEmm
ma:
wwwoo woo; oooo mood wmooo 3a; m. _woo go; 835% Eo>m<=2~¢<mm
Nvooo owo; wmooo ooo; omo _ .o no; 2 mo woo; £28m mﬁoo>nEImE
mwoo vow; «mooo Nmn; Rood w _o; 2 _o woo; moEooo oEUo>EHmE
rota coca rota hm Eooxd
hm Em Z<mm24 Em Bm Z<mm24 Em Bm Z<mmS§ Em Z<mm24 83.35 832:6
n3: “Em EBSEJ
58 on AEE 58 o“ 58 m Eon o 5905

 

.6525“ assoc 2: o6 6m.m.NE>&mome fogs 5:58:56 538 as oo mz<m2mq co 8382 ”E 632;

139

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

848 m8 8 _ 2 8.8 3.8 4.: 888 8.» «.38» En a:
88 8.3 88.8 _.2 8 _ .o n: 88 88 888 E 82
E _ .o 83 S. M .o _ 8... on _ .c _8... 888 83 £358 m§o~_<\.~m._
88 _88 28.8 83. 83 48.4 888 83. £88 832883
83 88.4 828 8:. 8:8 88 83 ~88 £28” .9855“
8:8 88.8 88.8 83. 8:. :3. 83 ~88 888 688.8
88.8 :3 888 :2 888 :3. :88 8.4 8288 88238
888 88 888 83. 888 88.4 :88 8.8 888 888238
83 8.2 88 8.2 82 . 8.2 83 6.2 888 8
888 8.2 88 ...2 mm; 8.2 83 8.2 8888 n:
888 8.2 8.8 8.8 $8 8.: 83 8.2 £28» 22358
88 8.8 88 8.8 88 8.: 83 8.3 £88 mE<>umm
83 8.8 $3 8.8 888 8.8 _88 8.8 828» $8288;
888 5.8 :8 8 $8 8.8 83 8.8 8288 822888
me
83 8.8 88 8.8 82 8.8 8.0 8.8 8888 558238
me
:8 3.8 88 88 .88 8.8 «88 88 888 582253
88.0 $3 688 Ed 588 $3 E88 58 £28» goggmm
:88 $3 888 83 88.8 $3 $88 a; 8888 goggmm
coca cm coca coca coca
am am 7:58,: am 7282.“ am am 72824 em 3 7282.8 2385 858m
Em 8: 88888
as 8 58 2 8m £5 .0. as _ 88> .883

 

 

 

 

 

 

 

 

 

 

 

88385 63888 65 .6 88.853 A225: 8:38.88 .883 as .8 mz<m23 .8 8382 8< 638

140

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

88.8 :88 8.8 88.8: 88.8 8.8 8.8 8.8 £288 8: 52
88.8 8.8 88.8 8.8 88.8 8.: 8.8 8.8 882888 .85 52
88.8 888.8 8 _8 88.8 8 :8 888.8 _88 88.8 82888 $808858
88 88.8 3.8 88.8 88.8 88.8 :88 88.8 882888 memos/Ema:
:88 :88 888.8 :88 888.8 :88 88.8 88.8 882888 .0858
888 E8 888 :8 888.8 :88 88.8 88.8 882888 .9888
888.8 88.8 888.8 88 88.8 88.8 888.8 888.8 82888 8882838
:88 :88 88:8 2 :8. 88.8 88.8 88.8 888.8 8288 8.8.2888
:88 88.8 888.8 3.8 888.8 :88 _888 88.8 882888 88
:88 :88 8.8 :88 _88 88.8 88.8 88.8 82888 88
88.8 88.8 88.8 8.8 88.8 88.8 :88 8.8 8288 88258.8
888 88.8 88.8 88.8 88.8 :88 :88 8.8 82888 823858
88.8 8.8 88.8 8.8 88.8 88.88 888.8 3.88 82888 8882888
888 8.88 88.8 8.8 88.8 8.88 888.8 8.88 882888 .8882388
m8
888 88.8 :88 :88 888.8 88.8 :88 88.8 88288 205823.88
m8
888 58.8 888.8 88.8 88.8 88.8 :8 88.8 88288 398823.88
8.88 :88 88.8 88.8 888.8 :88 :88 88.8 882888 8808558
:88 88.8 883.8 88.8 88.8 88.8 :88 88.8 888888 8808>$m8
28:8 28:8 28:8 283:
cm 88 28.82.: cm 88 28.82.: cm 88 2882: um 88 28.88,: 288.8 2388.88
88: “a: 88: 8888858
as 88 as 8: 58 m as _ 8288885
888258 035m 05

88 8.885288% p.838 8:83:58 08888 82:8 288 828.8288 .3 28822. 8< 288.8

141

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

a; .393 v._ 09.8 _.N wade mm.m 95.3 $353 Ema 82
m undo m4 www.mc ﬁm amino mad @546 «@358 Pm: 82
8N mcdv cm; m 8.3 mag Eadm 5; whodv «@203 mﬁnONZPm—m
8N mmmdv 3H.“ Nmodm ma; homdv 5; whodv wag/Soc mﬁmomzpmm
3N gig. cod _mwdm _N._ wmodv 3..— mwdv «$203 xOmumm
_m; oomdv I: mohdv $6 8 _ .8 3: «.de meooo xOmumm
nod mmodm ea; cmvém E..— avnhm Z”.— wmmﬁm «Aw/Sow nEEOREnE
:1 mmbdm m _ .m www.cm no; mmobm _m._ meSm «av/Soc mags—~33;
no; owmém VNN an _ .vm No; mhmém 3: mcmwm «av/Sow mm
a; w_m.mm wd 353 end $03” 3: mcmwm «AG/Soc an
no; omwém ad www.mm 5 ﬂ ._ mowém m; DAMN «av/Sow mats—035mm
em; www.mm mm: 3.3 No; me ~ .3 m; nvﬁmm mar/Soc maﬁa—~33;
mad maém ad maﬁmm N; 3.9mm m; ammﬁm «av/Sow mn<<>m>rmm
h; 854% m; v8.3 M: Qumém mg ammdm 5:280 UQ>n<<>m<Hmm
m; oamdg o; $5.3 m._ www.mﬁ w._ Svdm mmEoow mmEO>m<=2xEmm
m; aocd~ mod mmmdm ad moo. _N M: Stow «@358 WEIO>mE£mEmm
NN; ENS mm; wide om; omméc E; 33.8 «Av/Sow mEUu>n<Hmm
a; @360 M: 53 .8 mm; 3&3 E A 336$ mmzooo mQUw>n§Hmm
5:2 5:2 mm: hm «$22
hm 3m Z<mm35 Em Bm Z<mm$§ Em Bm Z<mm§q Em <mm24 9:585 ogogm
:2885 0:382
n3: 58 cm n5: 58 3 n5: ES m 83 _ awwcobm ommcoh

 

 

 

 

 

 

 

 

 

 

 

.mBBoEHm vitae 05 Mo .8886 0:388 Ems: away—um 0:38 «o mZ<m=zmA mo mix—mg nv< 033.

142

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

M: 25.8 2 858 N 3.8 m 2.8 £258 £802
_ 28.8 55 M88 1 8.8 m 2.8 £28 8552
3 :58 2 $58 25 R: 85 82.5. £258 ”$6”?me
E 85.8 2 80$ 3 85.; 85 82.; £258 363255
2: 82.9 82 52.8 3 an? 2 5.? £258 55me
2 58.9 2: 88.9 85 2.5.8 2 25.? £258 655mm
3 5.8.8 35 5.8 3 558 2 88.8 £258 £5255
3 $38 85 8.8 855 83.8 2 85.8 £258 25255
S 8.8 m 825 M55 ”:8 2 58 £258 A:
2 Em 55 835 2 5.8 in 858 £258 E
S 28.8 of 898 m: 58.8 3 838 £258 vu>ﬁ<<>m5m£
85 55.8 85 58.8 82 58.8 3 58.8 £258 ou>n<<>mﬁm£
2 825 2: ~25 2 :25 5 ~82 £258 $5233
85 58.2 2.. 825 a: $25 2 .982 £258 35232
85 ~82 2 35.2 35 832 85 252 £258 35032259
£5 5.2 85 n: 52 832 85 2.52 £358 memo>m523m£
3 5.8 3 88.3 3 8.8 85 85: £258 Eoggmm
3 £38 3 £35 3 85.2 85 85? £258 EBB/gm:
£2 5 £2 £2 5 £2
am am 2352: am z<mm2q am am 22,525 5m z<mm2q 2:35 052:8
.5: 55 8825 $05
as om £8 2 £5 58 m :8 2 2828 23.55

 

 

823038 03585 2.: mo 526055 $80 3%): ﬁwcobm 25:3 mo wZ<mqu mo mama—Se Hm< 2an

143

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

no.” «$3 mod 0.5: and agn— v.3 m. ﬂ 2 ”£388 Ema 62
N53 NS: 3 .w w _ .5; 5.: NYC: v.3 m. _ 2 «@280 Pm; 82
v.2 Ova m.m_ 5+2 #3 mdﬂ 3: ONE «Ex/Sow QOONZE‘mm
ES wham— mmé ﬁmﬂ wé adm— Zl odf «av/Soc mQMONEPmm
mné ms: 3.x eqw: m.m_ #6: #93 n8: «aux/Sow xommpmm
0.x $62 0.2 N6: @6 m. "N— v92 Eh: «AG/Boo xomum—m
as 36¢ v.0 362 Nd 3.3 56 5&3 meoow mag—035mm
NS cado o6.— Eda m6 2.3 56 K.V.mo adv/Soc mag—ORE?”
8.x Owen mcnm :68 5.: 3.68 Q: $.th mmzoow n3
w.m_ mmghm v.m_ 56% 2.2 $.ch 0.2 mmNR «@3800 mm
m mmde a6 mde 5.2 :12 0.: ma: «Av/Sow Uv>n<<>m>~mm
ow ﬂog 0: ohm— N.m~ ems“: v.2 ma: 9:280 Ou>n<<>m>rmm
Tom No.39 mdm n+3 mm 3.8% wﬁm 86mm «AH—Zoom mmﬁoiﬁmm
ﬁmm w _ .Nﬁo _N 9.96 mm wodvc wsm $68 «@3800 mat—815mm
5.3 Save mém 3.30 cNm 8.5% vﬁm N. _ mo «av/Sow mmEO>mEoREmm
m. I“ Yovc mm wmo 5mm ©0600 Em N. # me «@388 mgo>m\co§:\mm
We no. _ 2 SM 2: mmd S. _ I _.m 3.2: «AG/Sow mﬁov>m§mm
2% vde Wm om; : Nvé 3.2: ﬁn v0.2: «AG/Soc mEUn>n<HmE
hm Em Z<mm24 hm Em Z<mm24 hm Em Z<mmS§ hm Em Z<mm24 chimera Baozbm
REE :28th 0:282

58 ON “Em E8 A: man 58 m Sum _ coummaoﬁ .X.

 

 

.mohzosbm Bﬂxoc 05 mo cocooﬁv 0:388 aozmwco—o .x. we mZ<m2mq mo £92.92 6< 2an

144

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

”.2 mo: 3 as: M: 32 2:: 3: 828” E 52
n: no: 8:: 3: no 3: 2:: 3: £358 ha 32
3 SE 3; $2 a: $2 VS 22 £28» memomzﬁmm
«a no: ”.2 no: 0.: 3§ v3 22 £358 mEMONZPE
3 22 2: 32 he 32 2: ~32 £28» .655:
: a: 2: m. _2 Md 3.: 2: 8.8. $358 .0555
2: we 3 36 E RS 3 8 $358 $5325
3 3.8 2 3% 2. 9% 3 3 £58 ﬁaoacam
3 3.8 3. 3.8 8.0 2.6 ”3 NS 5.28” E
3 3.8 2 mac 3. w. a ”3 New £280 A:
S 32 3.2 2: ma 2.: 3 32 £28” %>&<>m\§
we 22 mod 32 3 in: M: 32 £358 Uu>a<>ehmm
3m 2% «a 88m 02 5mm 2.x a 328” $5353
Em 0.3m 3m 2.ch 2 WOW 3% mm mazes mmeoasmm
a. 3% s. N3 2 3% R 8.0% $28” mgo>maoasmm
3. $2 18 3.3 8.: 2% R 8.0% $280 m§o>mE2§mm
3 $2 2:. 9o: 3. E : MG 32 £28” Ems/SE
3“ .22 m3. 3 _ _ mm 32 3 32 £280 EBSHEE
um um
am am 5.32: am am z<mm§ 9m 235:: 9m 25ng 238$ ossgm
E: “a: 8:er
58 cm Em as S as m ea _ 9.80 seawaem .x.

 

 

.mobzosbm 2&5: 05 «o 582% 30.8 gamma—o .x. .«o mZ<m2mA mo max—made. Hn< 2an

145

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

M: 3.. 3 a3? 3 218m v.2 «QR £353 pm: a:
”.2 32 a: an ZN N3: «.2 2.3% £2280 h: 62
3 3;; 52 $2. 3 $8 2 3:. £28» mamoﬁpma
2 23:. 2 $22. 2 32¢ 2 3:. £358 56:35;
”.2 «23. 3 $5 a: 8.3 m2 ~22. £28” .655:
z :23 no 2. :1. _ _ 2;? n2 ~32. £358 .92th
E «a 3m 5.2m 2 3.9% 3m 3.3% $28” 353%
m2 ~38 3% ”no? on 3% 2m 33% £225 @595
v.8 3.8” E $8 0% ~55 «.3. $63 $28” “a
#3 $63 mam _ 35 MS $.02 34 $63 £358 .3
no 38 _.: 8.8V mom 3:. 3 528 £28” %>&<>m¢mm
mm 0.3m S N; 3 2.38 3. ~32. 8:58 oc>n<<>m5mm
2 3.2 3 2%: as 8m 3 $2 $28” mméoasmm
«mm 03:. M3 35 3 m3: 3 0.2m £280 :52»st
3 35m 3 2.8m mo 3% we 2.2m £28m mmEo>mE23mm

5.2 2% 92 3% 3 $3 we :22 £358 3:38:22st
n2 mwﬁ V2 3: 52 SE 2.2 5 £28” nabggmm
as 385 m3 2.2K Eu .3 :2 an $58 38>ng
am
am 25mg 5 2m 25mg am am 2&2): am am z<mm§ 2382 238%

QOUOUHMQ
mam: .mmohnw 23:0wa GomuwaO—m
£8 om 85 em ,3: 58 2 Ex 38 m .82 go 3382:.

 

 

 

 

 

 

 

 

 

 

 

.mohzosbm 0328c 05 no 2282:. 0:288 :23ch6 mo 26608 X. mo mz<m2mq MO 22293 uw< 03m...

146

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0.2 msom m6 0.2m a 5m; Wm m_.mmm £28m Hmm 82
9w 0.2 2m md 3.2 m 2 Nzumm m.» Edmm «AG/Soc Hm; 82
m.m_ odnm o woémm m6 02me no.2 one?” «AG/Sow QOONZme
Q: Nm.mmm QE $63 8.3 3.3m no.2 3.3m 5:280 mEMONZme
w.m_ 3.3m o 3. 5m ﬁom 3.x?“ wd mod? «Av/Sow .55me
WE $82 2.2 mmdhm W2 2.3m ad momﬁnm £280 xOmmFm—m
mm ©me 3 3.55” mm wd? v.2 21.2» 3353 mags—~83;
mm 3% mm 063 mdm wdmv Ymm 3va £226 mags—@572
93” 03 0.2 v.26 02 3.80 93 modmo .3203 mm
no.3 363 8:3 mm@ msm www.mvo me aodmc £358 mm
06 mmAmm v.2 3.0mm md— nmdmm Q2 vow £28m Uu>n<<>m>~mm
NH $me 2‘ 3.21:. 2: $.va Qm _ 3m $358 Uu>n<<>m>rmm
m.m cm. Sum v.0 VNde v ﬁmvm m.: and? £358 mmEo—btmm
Wm $.me Yo NNNVM Q: $.an m. 3 demm 3208 mmEoEEmm
ma:

mg.” 8.5% m.m 9va we 22% M; 3.3% «@358 EO>m<=o§Emm
ma:

Wm 3.21:. ON 3.03. 0.5 2.me ma 3.3m £358 EO>m<=2zEmm
m _ .3 m 2 .mwm tom N2 .03 3.2 2». Km m _ .2 3.5mm £28m mEUv>EHmm
2H2 ~2on :dN mdmm v.3 2.3% 2.2 3.3m £358 mEUP/QHmm
hm Em Z<mm22 hm Em Z<m2>§ Em Bm Z<mm24 Em Bm Z<mm24 2335 2:63am
5885 $80

. .395 gamma—2m

mm: 58 om A32 58 A: She Em “$3 58 m .§< go 3:622 .x.

 

 

 

 

 

 

 

 

 

 

 

33823 025$ 05 .8 53026 $80 aoumwcoﬁ .«o 2::on °\.. .20 mZ<m=2mq .«o 222“: Ho< 033.

147

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII

mil+1;leWWWml