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LIBRARY
Michigan State

TH€Sl3 ‘

University

This is to certify that the
thesis entitled

DEVELOPMENT OF ACTIVE PACKAGING FOR RETORT
FOOD; APPLICATION OF OXYGEN SCAVENGER

presented by

Yangjai Shin

has been accepted towards fulfillment
of the requirements for the

Master of degree in
Science

School of packaging

 

 

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Date

 

 

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PLACE IN RETURN BOX to remove this checkout from your record.
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2/05 c2/CfiCIDateDueJndd-p. 1 5

DEVELOPMENT OF ACTIVE PACKAGING FOR RETORT FOOD;
APPLICATION OF OXYGEN SCAVENGER

By

Yangjai Shin

A THESIS

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

MASTER OF SCIENCE
School of Packaging

2005

ABSTRACT

DEVELOPMENT OF ACTIVE PACKAGING FOR RETORT FOOD;
APPLICATION OF OXYGEN SCAVENGER

By
Yangjai Shin

The technology to extend shelf life in processed food has progressed due to
innovations in sterilization and barrier packaging. However, the passive packaging
systems cannot completely solve the problems of oxidation, odor and discoloration due to
oxygen dissolved in food, or contained in the headspace in the package. Oxygen
scavenger packaging can effectively solve this problem. The packaging system interacts
with inside of package, and removes headspace oxygen. In this research, three oxygen
scavengers with different content of iron (%) were applied in multilayer trays with
processed meat ball products, and evaluated products shelf life compared to passive
barrier packaging. The oxygen concentration in the headspace, oxidation of the product,
color, and flavor were evaluated periodically for samples that were stored at 23°C, 50%
RH and at 30°C, 80% RH for 9 months. The results showed that all three active packages

were superior to conventional passive packaging by removing headspace oxygen in the

packages.

AKNOWLEDGEMENTS

I would like to express my deepest heartfelt thanks to Dr. Susan E.M. Selke as
my advisor for her educational and professional guidance, timely advice, and keen sense
of humor.

I also would like to express my sincere appliciation to Dr. Bruce R. Harte and Dr.
Wesley N. Osburn for their research guidance and support as committee members. I am
grateful to Dr. Osburn and his research group for all the great input and collaboration in
this project. I would like to thank him for allowing me to use the lab equipment to finish
the evaluation of food.

I would like to thank Mr. Yongwook Park, who is a CEO of E.SAENG Co., Ltd.,
for encouraging me to develop this project successfully, and Mr. Ito and my company’s
members to develop the process technology of active packaging.

I would like to thank Joongmin Shin and Yunsuk Lee for sharing their expertise
and supporting me throughout my research, and all colleagues in School of Packaging.

Finally, my deepest appreciation goes to my family, my wife Ms. Yunyoung Huh,
two sons and my mother who supported me through the difficult times and while

accomplishing my course work.

iii

TABLE OF CONTENTS

Content page
LIST OF TABLES .................................................................................. vi
LIST OF FIGURES ................................................................................. vii
CHAPTER 1. INTRODUCTION ................................................................ 1
1.1 Recent trends in barrier packaging .................................................... 1
1.2 Problem statement of passive packaging ............................................ l
1.3 Introduction to active packaging ..................................................... 2
CHAPTER 2. LITERATURE REVIEW ....................................................... 5
2.1 Active packaging systems .............................................................. 5

2.1.1 Oxygen scavenger technology .............................................. 5
2.1.2 Ethylene scavenging technology ............................................ 9
2.1.3 Antimicrobial packaging ..................................................... 9

2.1.4 Humidity scavengers ....................................................... 11

2.2 Future ofactive packagmgll

2.3 Factors affecting permeability of EVOH ....................................................... 12
CHAPTER 3. MATERIALS AND METHODS .............................................. 14
3.1 Materials ................................................................................. 14

3.1.1 Containers .................................................................... 14

3.1.2 Product ......................................................................... 17

3.1.3 Storage conditions 18

3.2 Methods ................................................................................. 19

3.2.1 Oxygen concentration in package .................................................. 19

3.2.2 Color ............................................................................................... 20

3.2.3 TBA analysis .................................................................................. 21

3.2.4 Flavor evaluation ............................................................................ 23

3.2.5 Statistical analysis .......................................................................... 24

CHAPTER 4. RESULTS AND DISCUSSION ................................................ 25
4.1 Oxygen concentration in headspace ................................................... 25

4.1.1 Water packag1ng25

4.1.2 Meatball packaging test3l

4.1.3 Discussion ofpenneability............................... . . . 35

4.2 TBA. ....................................................................................................... 41

4.3 Color................. 45

4.4 Flavor 51
CHAPTER 5. CONCLUSIONS AND FUTURE WORK ................................. 53
5.1 Conclusions 53

5.2 Future work 54
APPENDIES .......................................................................................... 55
APPENDIX A: Oxygen concentration data (tray with meatballs) .................. 55
APPENDD( B: Oxygen concentration data (tray with water) ........................ 59
APPENDIX C: TBA data .................................................................. 61
APPENDD( D: Color data ................................................................. 63
APPENDIX E: Flavor data ................................................................. 65

REFERENCES ...................................................................................... 69

LIST OF TABLES

Table page

1. Construction configuration ofmeatball packaging 16
2. Oxygen concentration of the headspace of packages
filled with water after 180 days storage at C1 and C2 conditions ......................... 28

3. T-Test result for oxygen concentration in the headspace of packages

filled with water after 180 days storage ......................................................... 28
4. The structure of control tray and properties ................................................................... 36
5. Water vapor transmission value (WVTR) of each layer in multilayer structure ........... 40
6. TBA value for 6 months (plastic lid, 30°C, 80% RH) 42
7. TBA value for 6 months (plastic lid, 23°C, 50%RH) ..........43
8. Color (lightness: L) analysis data (plastic lid, 30°C, 80% RH) ............................ 48
9. Color (lightness: L) analysis data (plastic lid, 23°C, 50% RH) ............................ 49
10. Discrimination Index for each meatball package compared to fresh samples...........52
11. Oxygen concentration (meatball, EVOH lid, and 23°C, 50% RH)... . . . . ..........55
12. Oxygen concentration (meatball, aluminum lid, and 23°C, 50% RH) .................... 56
13. Oxygen concentration (meatball, EVOH lid, and 30°C, 80% RH)57
14. Oxygen concentration (meatball, aluminum lid, and 30°C, 80% RH) .................. 58
15. Oxygen concentration (water, aluminum lid, and 23°C, 50% RH)............. . .5.......9
16. Oxygen concentration (water, aluminum lid, and 30°C, 80% RH) ...................... 6O
17. TBA value (meatball, EVOH lid, 23°C, 50% RH) .......................................... 61
18. TBA value (meatball, EVOH lid, 30°C, 80% RH) .......................................... 62
19. Color analysis data of meatball packages (EVOH lid, 23°C, 50% RH) ................. 63

vi

20. Color analysis data of meatball packages (EVOH lid, 30°C, 80% RH) ................. 64

vii

LIST OF FIGURES

Figure page
1. The mechanism of oxygen scavenging in active packaging ................................. 4
2. Sachet type and polymeric type oxygen scavenger (iron based) ............................ 6
3. The effect of anti-microbial technique .......................................................... 10
4. Description of meatball packaging ............................................................. 17
5. Retort and heat sealing machine ................................................................ 18

6. Environmental chamber in the School ofPackaging (MSU) 19
7. Oxygen headspace analyzer .................................................................... 20
8. Colorimeter ........................................................................................ 21

9. TBAanalyzing equipment 22

10. Electronic nose .................................................................................... 24
11. Oxygen concentration with water (aluminum lid, 30°C, 80% RH) ....................... 26
12. Oxygen concentration with water (aluminum lid, 23°C, 50% RH) ....................... 26

13. Trend line of oxygen concentration with water (aluminum lid,
30°C, 80% RH) ..................................................................................... 3O
14. Oxygen concentration with meatballs (aluminum lid, 30°C, 80% RH). .......32

15. Oxygen concentration with meatballs (plastic lid, 30°C, 80% RH) . . . ....32

viii

16. Oxygen concentration with meatballs (aluminum lid, 23°C, 50% RH). .
17. Oxygen concentration with meatballs (plastic lid, 23°C, 50% RH) . .
18. Trend ofmalonaldehyde (plastic lid, 30°C, 80% RH)
19. Trend ofmalonaldehyde (plastic lid, 23°C, 50% RH)
20. Difference in lightness between T1 and T2 stored at C1 (30°C, 80% RH) .................
21. Trend ofL value (plastic lid, 30°C, 80% RH)
22. Trend ofL value (plastic lid, 23°C, 50% RH)
23. PCA group for meatballs after 9 months storage
24. Discrimination index (DI) for T1 and fresh samples............. ..
25. Discrimination index (DI) for T2 and fresh samples

26. Discrimination index (DI) for T3 and fresh samples

27. Discrimination index (DI) for T4 and fresh samples

..34

..34

...44

.44

.50

.50

..52

.65

.66

.67

68

CHAPTER 1. INTRODUCTION
1.1 Recent trends in barrier packaging

In the past twenty years, the use of plastic packaging has grown remarkably,
because of its convenience for manufacturing, handling, and use [25]. In particular, multi-
layer barrier packaging has challenged metal and glass for long shelf life food packaging,
because of its high barrier properties, as well as its versatility and convenience. For this
reason, this barrier packaging market has grown rapidly, and was projected to reach $3.8
billion in 2003 [26]. One of the largest segments of the multi-layer barrier packaging
market is ethylene vinyl alcohol (EVOH) [1 1]. Research shows that the growth rate of
EVOH was more than 10% in the barrier material market, for the years 2001 to 2005 [2].
The demand for high gas barrier packaging materials drives the growth of consumption
of ethylene vinyl alcohol (EVOH). Typically, EVOH has been coextruded with moisture
barrier layers because of its moisture sensitivity. Specifically, EVOH based multi-layers

barrier packaging is very common in food packaging because of its excellent barrier

properties.

1.2 Problem statement of passive packaging
Due to its sensitivity to moisture, EVOH has some limitations at high humidity
conditions. For example, the atmosphere inside of a package cannot maintain a constant
gas or moisture concentration during the retort process. EVOH based multi-layer
packaging will be influenced by the atmosphere around the food because EVOH has poor
moisture barrier properties. Another problem is the presence of oxygen in the food itself

and within the headspace of the package. In particular, it is difficult to control or remove

headspace oxygen during packaging. Oxygen in the headspace of the packaging and in
the food itself can cause off-flavor, color change, nutrient loss and increase microbial
growth, even though the multi-layer packaging provides excellent protection from the
environment. For this reason, new technology using an oxygen scavenger material, as one
type of active packaging, was introduced to replace or supplement conventional multi-
layer barrier packaging or passive packaging. The oxygen scavenger material is designed

to control oxygen inside the package and provide a barrier to environmental oxygen [24].

1.3 Introduction to active packaging

Active packaging, which is often referred to as “smart packaging,” is intended to
sense internal or external environmental changes and modify [the internal packaging
environment by modifying its own properties. Therefore, the goal of active packaging is
to extend the shelf life of contained food and beverage products either to remove oxygen
or prevent it from entering the in-package environment, minimizing undesirable oxidative
reactions [1].

The widely known commercial oxygen scavengers are ferrous compounds,
catechol, ascorbic acid and analogues, ligands, oxidative enzymes such as glucose
oxidase, unsaturated hydrocarbons and polyamides [10]. The most general oxygen
scavengers in commercial use are ferrous iron. The primary compound is ferrous iron
oxide, which oxidizes to the ferric state. The water activity in food must be above some
minimum moisture requirement to oxidize the iron compounds. The level of minimum
requirements varies. One of the general reaction mechanisms for iron oxidation is as

follows:

Fe -> Fe+2 + 2c -

V202 + H20 + 2c" 9 ZOH‘

Fe+2 +20H‘ -> Fe(OH)2

Fe(OH)2 + ‘/4 O; + 1/2 H20 -) Fe(OH)3

Typically, iron-based materials have a high oxygen scavenging capacity and are

relatively less expensive than the other scavenging materials previously mentioned.
However, since they include iron compounds, iron based scavenging materials interfere
with metal detection and the visual clarity of the package. On the other hand, organic
based oxygen scavenging materials have good transparency and allow use of metal
detection, which is important in food packaging. Despite these advantages, their low
oxygen scavenging capacity and high cost are innate problems of these systems. When
oxidation occurs, they can also generate undesirable odor compounds such as ketones or
aldehydes. Thus, choice of an appropriate oxygen scavenger depends on the type of
packaging used and the type of product. As a conventional application, the use of discrete
sachets containing oxygen scavengers previously mentioned has already found
commercial application. Inserting a sachet into the package is effective but meets with
resistance from food packers, because it is visually unappealing, especially if the sachet is
broken. Also, accidental ingestion of the sachet by children is a concern. Thus, a much
more useful approach would be the use of multilayer plastic barrier packaging as the
scavenging medium [Figure 1]. For this reason, in this research, ferrous iron based
oxygen scavengers, which can be extruded and have high performance even in retort

conditions, were selected to evaluate the shelf life of food.

Passive Packaging Active Packaging

   

 

Outside Inside Outside Inside
. 02 . 02 .
a O
_ 02
O
0 O
O . T O
O
0
Oxygen Scavenger

Figure l: The mechanism of oxygen scavenging in active packaging

CHAPTER 2. LITERATURE REVIEW
2.1 Active packaging systems

Active packaging is packaging systems that interact with the internal gas
environment of the package to extend the shelf life of products (mainly food). The
technology modifies the internal environment and interacts with the foods, by removing
gases or adding gases to the headspace of the package. Major active packaging
techniques include substances that absorb oxygen, ethylene, moisture, carbon dioxide,
and odors while others release carbon dioxide, anti-microbial agents, antioxidants and

flavors.

2.1 .1 . Oxygen scavenger technology

The presence of oxygen in food packages can cause food spoilage, creating off-
flavors, color changes, nutrient loss and microbial growth. Although oxygen sensitive
food can be packaged using modified atmosphere packaging (MAP) or vacuum
packaging, neither technique can effectively maintain 0% oxygen inside the package
because they are not able to totally prevent oxygen permeating through packaging film,
or oxygen contained in the food itself. Oxygen scavenger systems are one of the most
promising applications of active packaging. An oxygen scavenger absorbs residual
oxygen in the package and extends shelf life by preventing oxidation and aerobic
microbial growth. In general, existing oxygen scavenger technologies use one or more of
the following concepts: iron powder oxidation, ascorbic acid oxidation, photo sensitive
dye oxidation, enzymatic oxidation, unsaturated fatty acids, or immobilized yeast on a

solid material.

2.1.1.1 Iron based oxygen scavenger

The most widely used oxygen scavenging system in commercial use is iron
oxidation, which is discussed in chapter 1. The sachet types of oxygen scavenger systems,
like Ageless (Mitsubishi Gas Chemical CO, Japan) or Freshpax (Multisorb Technologies
Inc., USA) are the most common type [10]. However, since a potential risk of accidental
ingestion of a large amount of iron exists, recent trends are to incorporate the iron
compound into the package. Low molecular weight iron based ingredients are dissolved
or dispersed in a plastic or the plastic may be made from a polymeric scavenger, such as
Oxyguard (Toyo Seikan Kaisha, Japan) [19]. The iron based absorber can be incorporated
into a laminate, which can be found in packages of many foods: cured meat, cookies,

pastas, and so on.

   

Figure 2. Sachet type and polymeric type oxygen scavenger (iron based)
2.1.1.2. Ascorbic acid oxygen scavenger
Another oxygen scavenger technique is ascorbic acid oxidation. Oxygen in the
package oxidizes ascorbic acid to dehydroascorbic acid, so oxygen in the headspace of
the package is removed. Since ascorbic acid is a six-carbon compound, a high weight is
required to get enough oxygen absorption capacity. Its slower absorption rate compared

to iron based oxygen scavengers is another drawback. Darex (Grace, Lexington, MA,

USA) is an example of this technology. It is designed to be incorporated into barrier
packaging such as crown caps, plastic or metal closures. The company reports they

extend the shelf life of beer by 25% [12].

2.1.1.3. Light activated oxygen scavenger
Photosensitive oxidation is the basis for an oxygen scavenger system that consists

of sealing a small coil of an ethyl cellulose film containing a dissolved photosensitive dye
and a singlet Oz acceptor in a transparent package. By using lights with appropriate
wavelengths, the dye molecules are excited, and then pass their excitation to oxygen as it
diffuses into the film from either the package headspace or from the liquid food. The
excited O; molecules react with the acceptor and then are consumed. While the film is
illuminated, the process continues until all the oxygen reacts. The reaction scheme is the
following [21]:

Photon + dye --> dye“

dye“ + 02 --> dye + 02*

02* + acceptor --> acceptor oxide

02* --> 02
This photochemical process has advantages because it does not need sachets in the food
package and works regardless of humidity. The first used dye was erythrosine, which is
an FDA approved food color additive, plus a color sensitizer that is bleached by light. For
singlet oxygen acceptors, several materials were tested: difurylidene erythrito (DEF),
tetraphenyl prophine (TPP), dioctyl phthalate (DOT), and dimethyl anthracene (DMA).

However, these are not approved for food contact. This type of oxygen scavenger does

not initiate in the dark. Therefore, this technique cannot be used with non-transparent

film. An example of a light-activated scavenger is Zer02TM (CSIRO, Australia) [10].

2.1.1.4. Enzyme based oxygen scavengers
Another oxygen scavenger technique uses enzyme reactions. The enzyme
responds with a specific substance to scavenge incoming 02. Glucose oxidase is a
popular oxygen scavenging enzyme. Glucose oxidase transfers two hydrogens fiom the —
CHOH group of glucose to oxygen with the formation of glucono-delta-lactone and
hydrogen peroxide. The reaction is the following:
20 +202+2H20 --> 200 +2H202
where G is the substrate.
However, H202 is a highly oxidizing agent and therefore objectionable, so catalase is
introduced to break down the peroxide [10]:
2H202 + catalase --> 2H20 + 02 + catalase
From the two reactions above, the original oxygen is reduced by half, and ultimately it
will become zero. The glucose plus catalase enzyme system is very sensitive to pH, water
activity, temperature, and various other factors. Also, it requires water for activation, so it
cannot be used for low humidity products. A commercially available sachet style oxygen
scavenger of this type is the Bioka (Bioka, Finland) [22]. These oxygen scavengers can
be used alone or in combination with MAP. Obviously, using them alone eliminates the
MAP step and increases packaging speed. However, industry commonly removes oxygen
through MAP and then uses a small amount of oxygen scavenger to remove residual

oxygen in the package and maintain its concentration at less than 0.1% [20]. In addition,

to use oxygen scavenger techniques effectively, a package with a high barrier to oxygen

is required.

2.1.2. Ethylene scavenging technology

Ethylene (C2H4) on flesh fluits accelerates ripening and softens vegetables.
Therefore, to extend shelf life, the accumulation of ethylene in the packaging should be
removed. The ethylene-scavenging agents incorporated into packaging film trap ethylene
produced by ripening fluit or vegetables. The reaction is irreversible and only small
quantities of the scavenger are required to remove ethylene at the concentrations at which
it is produced. Nevertheless, these systems are not yet very successful because they do
not have enough ethylene scavenging capacity. A large amount of flesh fluits and
vegetables are lost due to fungal contamination and physiological damage [7]. Eventually

however, this technique will contribute to an increase in ability to export flesh produce.

2.1.3. Antimicrobial packaging

To prevent or inhibit undesirable microbial growth on products, antimicrobial
substances can be incorporated into or coated onto food packaging materials. The
principle of antimicrobial action is based on the release of antimicrobial agents flom the
packaging to the product. The major potential applications are food products like meat,
fish, poultry, cheese, fluits and vegetables [22]. Figure 3 shows that the blueberries in
the package incorporated with an antimicrobial agent on the right side of the figure were
kept flesher than those on the left. Many new antimicrobial systems have been

developed [14]. Currently, nisin is the best-known coated type of antimicrobial agent.

This natural compound has been well characterized as a food preservative and has
attained GRAS status (generally recognized as safe) [22]. Sorbic acid and potassium salts
are also well known food preservatives with antimicrobial activity. Many of the
incorporated antimicrobials are not yet permitted for food use. Silver-substituted zeolite
is the most common antimicrobial agent incorporated into plastics. However few
descriptions of the effectiveness of this material have appeared and the regulatory status
of the addition of antimicrobial components into foods has not been clarified in the US or
Europe. Moreover, the choice of which antimicrobials to incorporate into packaging is
often limited by the immiscibility of the component with the packaging material or by the
heat sensitivity of the component during extrusion [10]. These types of antimicrobial

agents are still being studied and developed to ensure their safety and effectiveness.

 

 

Figure 3: The effect of antimicrobial technique. The package on the lefi without
antimicrobial agent has a significant growth of mold; the package on the right contains an

antimicrobial agent.

2.1.4. Humidity scavengers

Some foods are easily damaged by moisture. In high moisture barrier packaging,
moisture inside the package is trapped in the package, and then trapped moisture may
condense in the package and be absorbed by the product. Therefore, food can became soft
and lose consumer appeal. Conversely, excessive water evaporation through the
packaging material may result in drying and hardening of foodstuffs. Some of these
moisture problems can be controlled by using humidity scavengers. A certain amount of
moisture can be trapped in the package, and maintain proper moisture content. Food
manufacturers can use a film with the appropriate water vapor permeability or use a
desiccating film or moisture controlling sachet or pad. Often, the purpose of moisture
control is to lower water activity, to inhibit the growth of mold or bacteria in high water
activity foods like ready-to-eat meals [10].

Silica gel is one of the most common desiccants and is used in a wide range of
food, as well as non-food products such as pharmaceuticals, to maintain a low humidity.
Another application type removes melting water flom flozen or flesh food. Drip-
absorbent sheets like Termariate (Australia) or Peaksorb (Peak Fresh Products, Australia)
are examples. These applications control liquid water in high water activity foods such as

meat, poultry, fluits and vegetables [22].

2.2. Future of active packaging
The technologies discussed above are only some of the commercial and non-
commercial applications of active packaging. This technology is the subject of research

in many countries and rapid developments may be expected. However, in the food

11

industry, there is still concern about introducing active components to packaging because
consumers may consider the components harmful and may not accept them. To avoid
such concerns and permit further development of these techniques, consumers should be
more informed, using reliable information channels [23]. In addition, even if those active
packaging techniques may be beneficial in extending shelf life, a holistic approach to

environmental impacts needs to be considered as well as economic profits.

2.3. Factors affecting permeability of EVOH

Permeability is a measure of how easily a perrneant compound transports through
a solid medium. High permeability indicates that the solid material poses little resistance
to the transport of the permeant. The chemical structure of the polymer and perrneant are
the primary factors in determining the barrier properties. The main reason for designing
multilayer structures in packaging is enhancement of overall barrier properties to
moisture and gas. EVOH is one of the most commonly used barrier materials. It has
excellent gas and organic vapor barrier properties as long as the polymer is not exposed
to high humidity conditions. Since EVOH is a polar hydrophilic polymer, moisture will
act as a plasticizer that increases the flee volume of the polymer, and the overall
permeability will be increased greatly compared to dry conditions [17, 18]. For this
reason, EVOH is always used between high moisture barrier polymer layers like PP and
PE.

Another factor that can change permeability is storage temperature. The

following equation shows how it affects permeability.

P = P0 exp(-Ea /RT) (2.1)

12

where E. is the activation energy, R is the gas constant, P0 is a pre-exponential term and
T is temperature in Kelvin. If a value of permeability, P, is given at temperature T1, the

value of the permeability P2 at T2, can be calculated if E3 is known [17].

Ea .1";
P, -1), -exp[ R (T. Tzii (2.2)

Thus, the equation 2.2 can be written as

 

P2=Pi'f

E 1 1
= .. ____ 2.3
expikin Ti] ( )

where,

 

13

CHAPTER 3. MATERIALS AND METHODS

3.1 Materials

3.1.1 Containers

The container was composed of a tray and a lid. The tray was thermoformed flom

a sheet that has a multilayer structure produced by a feed-block system in a coextrusion
sheeting line. The tray was designed as a multilayer structure,
PP/adhesive/EVOH/adhesive/OS (Oxygen Scavenger)/PP. To prepare the oxygen
scavenger resin, the oxygen scavenger was mixed with PP, extruded and pelletized to
produce masterbatch resins. Then, PP resins were blended with the desired amounts of
masterbatch resins to produce the final matrix film layer with a homogeneous
concentration of oxygen scavenger compound. For this research, the content of oxygen
scavenger masterbatch in the OS layer was controlled to 100, 80, and 40%. Iron based
compounds which are activated by moisture during the retort process and storage were
used as the oxygen scavenger. As shown in Table 1, the concentration of oxygen
scavenger in T2 was 2.5 times and that of T3 was 2 times that of T4. The oxygen
scavenger of T2 was flom a different company than those of T3 and T4. The gas barrier
layer was 25 um of EVOH resin containing 32% ethylene. PP was selected as the
moisture barrier material. A material was chosen for the tie layer that could be used in
retort conditions. In this study, the details about parameters and process for the oxygen
scavenger film extrusion, the names of the oxygen scavengers, and activation conditions
will not be specifically reported due to a confidentiality disclosure agreement with the

packaging manufacturer. T1 was used as a control, with the conventional barrier material

14

structure PP/adhesive/EVOH/adhesive/PP, for comparison to the three oxygen scavenger
packages. (T2, T3, T4)

The lids for the trays were traditional cast film structures for retorting:
PET/Nylon/EVOH/PP. The film was produced by a triple dry lamination and slitting
process, and printed by roto-gravure.

The EVOH barrier layer contained 32 % ethylene. Biaxially oriented nylon was
selected for its excellent pinhole resistance. For the sealing layer, cast PP film was
laminated to serve as the inside of the lid. Lids containing an aluminum foil layer were
compared to the lids containing EVOH. The structure compositions are described in

Table 1.

15

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3.1.2 Product (food and process conditions)

As a sample product [Figure 4], meatballs were selected because they are one of
the most common retort foods that are commercialized in Korea, and both the meat and
the oil in the sauce are sensitive to oxidation. Since the meatball tray has a larger
headspace than other retort food packaging, the package provided enough samples to
analyze oxygen concentration inside of the retort packaging. The retort condition was
one hr at 121°C (come up time: 10 min, retort time: 35 min, cooling time: 15 min). In
order to reduce food oxidation in the package, a controlled and modified atmosphere
packaging system was used. The mixed N2 and C02 gas was flushed into the headspace
in the package before the lid was sealed. The proportion of C02 gas was limited to 50%
because the meatball package (tray) tended to distort when the gas dissolved in the water
of the food, even though the package was specially designed to resist distortion. The
heat-sealing condition was 190°C to 210°C at a pressure of 2.5 kg/cmz, for 2 seconds.

The equipment is shown in Figure 5.

 

Figure 4: Description of meatball packaging

 

Figure 5: Retort and heat sealing machine

3.1.3 Storage conditions

Sample products were stocked in storage chambers [Figure 6] at two conditions
(C1, C2). The C1 condition consisted of light at a level of 800-1 ,000 lux, temperature of
30°C and 80% RH, which was considered as a summer season. The high humidity
condition was used to compare the barrier properties of the EVOH containing and the
aluminum lid, since the permeation of oxygen through EVOH rapidly increases above
80% RH. The other condition, C2, consisted of 23°C, 50% RH and dark. C2 was set up
as an annual average condition. All packaged samples were delivered flom Korea to the
laboratory of the MSU packaging department. Overall shipping time was 20 days and
total storage period was 250 days, including delivery time. Tests were performed at 30,

45, 60, 120, 180, 225 and 270 days after filling

 

Figure 6: Environmental chamber in the School of Packaging (MSU)

3.2 Methods
3.2.1 Oxygen concentration in package

The presence of 02 in a packaged food is often a key factor that limits the shelf
life of a product. Oxidation can cause changes in flavor, color, and odor, as well as
destroy nutrients and facilitate the growth of aerobic bacteria, mold and insects.
Therefore, the evaluation of oxygen concentration in the headspace was considered as a
major factor of this project. The oxygen concentration was measured using an Oxygen
Headspace Analyzer Model-3500 (Illinois Instruments). Samples were withdrawn at a
rate of 40 ml/min using the pump, and passed by the oxygen sensor. In the first set of
experiments, the efficacy of the oxygen scavenger was evaluated without food. Sample
trays were filled with distilled water and tested during a 6 month period, and absorption
of oxygen by the oxygen scavengers was evaluated by measuring oxygen concentration.
The control sample tray was compared to the oxygen scavenger packages. In the second
set of experiments, the retort trays with meatballs were tested to evaluate the performance

in the practice of oxygen scavenger with meatballs. Trays were filled with meatballs, and

headspace concentration was measured over a 9 month period. Oxygen concentration was
measured 8 times over the 9 months: 7, 15, 30, 60, 90, 120, 180 and 270 days afier filling.
The oxygen scavenger efficacy tests with distilled water were performed simultaneously
flom 0 days to 180 days. Tests for the first and second terms (0 and 7 days) were
performed at the laboratory of E.Saeng Co. Ltd (Korea), while awaiting delivery of the

sample to MSU packaging department (USA).

 

Figure 7: Oxygen headspace analyzer

3.2.2 Color

The color change corresponding to the oxidation of the surface of the meatballs
and the sauce was evaluated using a colorimeter instrument (Minolta Chroma Meter
Measuring Head CR—300), which was calibrated by using a reference tile, with a focus on
the change of the lightness of the food by measuring the L-value, rather than on other
color factors such as the a and b-values. Four packages (flom T1 to T4) were stored at
two conditions as described previously (3.1.3). Each sample color was measured twice,
and two samples were used for each of the four package configurations for each storage
condition. Then, all results for each package were averaged. For this test, samples were

tested 7 times over 9 months: 30, 45, 60, 120, 180, 225 and 270 days after filling.

20

 

Figure 8: Colorimeter

3.2.3 TBA analysis

TBA is well known as the most widely used test method for measuring the extent
of lipid oxidation in foods such as meat products. The general principle of this method is
the reaction of one molecule of malonaldehyde and two molecules of TBA to form a red
malonaldehyde-TBA complex, which can be quantified by spectrophotometry. The
procedure and determination were as follows: 10 g of ground meatball was weighed into
a 100 ml plastic bottle containing 50 ml of distilled water, and homogenized with 10 ,ul
antioxidant solution (Tenox S-food grade BHA+BHT). A polytron mixer (PT-35,
Kinematica, AG, Switzerland) was used to homogenize the mixture on speed setting 4 for
1 min. The meat homegenate was transferred to a 500 ml extraction flask; 2.5 ml of HCl
solution was added (1 :2, HCl:H20 v/v), and 1 ml of sulfanilarnide solution (1% WW)
was mixed in. With adding 47.5 ml of ionized distilled water, the total of the meat
homogenized solution volume became 100 ml; 50 ml (meat homogenate itself) + 2.5 ml

(HCl) + 47.5 ml (distilled water). The homogenized solution was placed in graduated

21

cylinders under spouts and 50 ml was distilled. Then 5 ml of the distilled solution was
pipetted into a plastic disposable tube (13 x 100 mm), and 5 ml of thiobarbituric acid
solution (0.003 g/rnl,TBA/distilled water) was added. The mixture was vortex mixed and
incubated in a boiling water bath for 30 min to develop color. Then the sample was
cooled in ice-water for 10 min and the absorbance of the resulting supernatant solution
was determined at 538 nm against a blank containing 5 ml of distilled water + 5 ml of
TBA solution. The optical density was multiplied by 7.8 to determine the amount of TBA,
expressed as milligrams of malonaldehyde per kilogram of meat. 10g of meatball sample
was collected flom each of four different areas in the container, and separately analyzed
for TBA value. Two containers were tested for each treatment (T1, T2, T3, and T4). Thus
the total tested samples were eight for each type of package. The test was performed 5
times over 6 months: 30, 45, 60, 120, and 180 days after filling. Figure 8 shows some of

the test equipment in the TBA analysis.

 

Figure 9: TBA analyzing equipment;

(a) Spectrophotometer, (b) Water Bath, (c) Condensation and Distillation

22

3.2.4 Flavor evaluation

Flavor, comprised of aroma and taste, is an important food quality factor.
Generally, sensory analysis by panels of specially trained persons and instrumental
analysis methods such as gas chromatography (GC), GC with mass spectrometry (GC-
MS) or high performance liquid chromatography (HPLC) are used for flavor evaluation.
For sensory testing, the most important problems include the standardization of
measurements, the correctness of training, and the stability and the reproducibility of the
evaluation. They affect the measurements, which are also difficult to compare between
different panels. The relatively high costs for training and use of sensory panels are also a
major drawback of this technique [6]. The analytical methods are time-consuming and
expensive, and require skills in operating the equipment and interpreting the results.
Recently, electronic nose instruments have been introduced and are increasing in use
because of their success in monitoring the flavor of food [8]. To measure the flavor
change of the meatballs, an E—nose (FOX 3000, Alpha MOS) was used. The FOX 3000
system with two metal oxide sensor arrays (consisting of 12 sensors) was used. Each
sensor has different sensitivity and selectivity to various chemical compounds. Therefore,
a combination of several sensors provides a unique fingerprint of the samples. It allows
determination of any variation in the headspace volatiles of the samples. Figure 10
shows the Fox 3000 system used in this test. The robotic auto sampler of the Fox 3000
system took sealed vials containing 1 g of meatball samples to an oven, syringed out a 10
ml gas sample flom the headspace, and injected it into the sample injection port. The
carrier gas that flowed through the sensor carried the sample gas, and sensors analyzed it.

For this test, samples were tested at the end of 9 months: 270 days afier filling. Six vials

23

which contained lg of meatball were prepared for the E-nose test, for each
package/storage condition combination. The response obtained flom the sensor arrays

were processed using principle component analysis (PCA).

 

Figure 10: Electronic nose

3.2.5 Statistical analysis

Two-way analysis of variance (AN OVA) using SAS Statistical Analysis System
(SAS Institute Inc, Cary, NC.) was performed to analyze the results at the 95%
confidence level (p=0.05) using the Tukey’s honestly significant different multiple

comparison test.

24

CHAPTER 4. RESULTS AND DISCUSSION
4.1 Oxygen concentration in headspace

4.1.1 Water packaging test

4.1.1.1 Results and discussion

Figure 11 and Figure 12 show the trend of oxygen concentration in the headspace
of packages filled with distilled water during 6 months of storage. The lid contained an
aluminum barrier in order to estimate the effect of the performance of oxygen scavenger
compared to conventional passive barrier packaging (T1). The initial oxygen
concentration in the headspace was 3%. Under the C2 condition (23C, 50% RH) [Figure
12], the oxygen scavenger packages (T2, T3 and T4) were superior to the passive barrier
packaging (T1) in maintaining a low oxygen concentration in the package headspace. T2
and T3 reached an oxygen concentration of 0% in the headspace within 1 or 2 weeks after
the filling and retorting process, while T4 reached 0% by 4 weeks. In contrast, the
oxygen concentration in T1 continuously increased.

Under the Cl condition (30C, 80% RH) [Figure 11], T2 maintained the oxygen
concentration below 0.5% in the headspace. Due to the increased oxygen permeation due
to higher temperature and humidity, the oxygen concentration of T4 after 6 months was
the same as that of T1 after 1 month. For T1, oxygen concentration rapidly increased to
12% flom 3%, and passed 10% within 1 month. Therefore, if the package needs to
sustain an oxygen concentration at 3% or below the original level, T2 or T3 should be

selected.

25

 

 

Oxygen concentration vs. time profile

18.000
16.000
14.000
12.000
10.000
8.000
6.000
4.000
2.000
0.000

Concentration (%)

0 50 100 150
Time (day)

 

200

 

—+—n
—*~n
"inn
-x—n

 

 

 

Figure 11: Oxygen concentration with water (aluminum lid, 30°C, 80% RH)

 

 

Oxygen concentration vs. time profile

12.000
10.000
8.000
6.000

4.000

Concentration (%)

2.000

0.000
0 50 100 l 50

Time (div)

 

200

 

 

—c—T1
-n~n
"*"U
—x-m

 

 

 

Figure 12: Oxygen concentration with water (aluminum lid, 23°C, 50% RH)

26

 

 

4.1.1.2 Statistical comparison between Cl and C2

Statistical analysis was done in order to see the difference in oxygen
concentration in the headspace of containers filled with water after 6 months between the
passive and active packages, between the active packages, and between the storage
conditions [Table 2]. Analysis of variance (ANOVA) was performed using the General
Linear Models procedure of the Statistical Analysis Software program (SAS Instituge Inc.
Cary, NC.) at the 95% confidence level (p = 0.05). Differences among variables were
tested for significance using Tukey’s honestly significant different multiple comparison
test, and the results are shown in Table 3. T1 was significantly different (p = 0.05) flom
the active packaging (T2, T3 and T4). T2 had the greatest capacity to absorb oxygen
among the active packages. T3 was better than T4 at any storage condition. Comparing
C1 and C2 with the same containers, for example TlCl vs. T1C2, the oxygen

permeability of all samples increased at C2.

27

Table 2: Oxygen concentration of the headspace of packages filled with water after 180
days storage at C1 and C2 conditions

 

 

 

 

 

 

 

Container c1 (30°C, 80% RH) (:2 (23°C, 50% RH)
T1 lO.113:l:0.400a 16940104553
T2 0.000i0.000b 0.32810.040b
T3 0.133zl:0.044c 02742021412
T4 0.228:t0.017d 10.733: 0.306b

 

 

 

Mean :l: standard deviation

(Unit: %, n = 3)

Table 3: T-test result for oxygen concentration in the headspace of packages filled with

water after 180 days storage: Results are all significantly different at the 95% confidence

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

level (p=0.05)
Group Condition Two-sample p-value
T1 vs. T2 9.26E—03*
, Cl T1 vs. T3 1.411302"
1) Pais‘ve Via T1 vs. T4 1.94E-03“
acme pac 868 T1 vs. T2 13213-02"
C2 T1 vs. T3 1.32E-02*
T1 vs. T4 1.35E-02*
T2 vs. T3 1.77E-04*
C1 T2 vs. T4 1.89E-04*
2) Amm‘g active T3 vs. T4 1.9513-02*
packages T2 vs. T3 29513-01
CZ T2 vs. T4 1.45E-O3
T3 vs. T4 2.46E-02
T1 C1 vs. C2 4.07E-05*
3) Between storage T2 C] vs. c2 l.46E-02*
condition T3 (:1 vs. cz 1.09E-04*
T4 or vs. c2 1.71E-O4*

 

 

 

 

 

 

 

 

Significant differences are indicated by *

28

4.1.1.3 Trend / Regression line

In general, food manufacturers in Korea often ask packaging companies to
provide data for the oxygen concentration as a function of storage time under the worst
storage conditions such as C1 (30 'C , 80% RH) in order to decide the shelf life of a new
food product when they develop it. Since all packages (T1, T2, T3, and T4) were sealed
with aluminum lids to prevent oxygen permeation flom the lid area and filled only with
water in order to avoid the reduction of oxygen concentration in the headspace of
packages flom oxidation by the food or sauces, the effects of active packaging using
oxygen scavengers could be calculated and estimated by the equation. From the results
of oxygen concentration for the C1 condition (30C, 80% RH), the trend line equation and
R2 value were determined using Micro Excel of the MS Office 2000 program. Six types
of trend lines (linear, logarithmic, polynomial, power, exponential and moving average)
were available. As measured by the R2, the oxygen concentration in T2, T3 and T4 was
best determined with a polynomial fit (2"d order) and for T1, the best R2 value was flom a
logarithmic equation. The best fit equations and corresponding R2 values were as

follows:

T1: y = 4.0496ln(x) — 2.5702, R2 = 0.9444
T2: y = 41305::2 — 00061:: + 0.1992, R2 = 0.8677
T3: y = 313-042:2 — 0.0195x + 0.527, R2 = 0.997

T2: y = -9E-06x2 + 0.0577x + 0.8473, R2 = 0.9596

29

 

20.000

15.000

E

5"

Concentration (%)

(5.000)

 

Oxygen concentration vs. time profile

 

Time (day)

 

 

0 T1
I T2
A T3
:1: T4
"'-L°8- (T 1)
—Poly.('1‘4)
—Pon.(T3)
—Poly. (T2)

 

 

Figure 13: Trend line of oxygen concentration with water (aluminum lid, 30°C, 80%

RH)

30

 

4.1.2 Meatball packaging test

4.1.2.1 Results for C1 (30°C, 80% RH)

The results for headspace oxygen concentration in meatball packages are shown
in Figure 14. In the evaluation of the meatball products, T1 also exhibited much higher
oxygen concentration in the headspace than did the oxygen scavenger packages.
However, it was lower than the oxygen concentration in packages filled with distilled
water. This is because of complicated mechanisms such as oxidation and chemical
reactions by lots of components in the food. The initial oxygen concentration in the
headspace was designed to be 3%, the same as for the distilled water.

Using the aluminum lid under the C1 condition (30°C, 80% RH) as shown in
Figure 14, the active packages (T2, T3 and T4) had a lower oxygen concentration in the
headspace than the passive barrier package (Tl ). The remaining oxygen in the headspace
of the active packages was removed perfectly after 1 week compared with T1 which
reached 0% oxygen only after 6 months.

Using a plastic lid laminated with EVOH film under the same condition (Cl) as
shown in Figure 15, the oxygen concentration in the headspace of the packages was
reduced, but none of the active packages sustained 0% oxygen concentration for several
months as did those using the aluminum lid. The oxygen concentration of T4 was
increased compared with T2 or T3. This seemed to mainly result flom the rapid increase

in oxygen permeability of the EVOH film in high humidity, over 70% RH [Figure 19] [4].

31

 

 

Oxygen concentration profile with meatballs

 

O 50 100 150 200 250 300
Time (day)

 

 

“uh-'13
--X--'Iit

 

 

 

 

Figure 14: Oxygen concentration with meatballs (aluminum lid, 30°C, 80% RH)

 

Oxygen concentration profile with meatballs

4.50
4.00
3.50
A 3.00
7.; 2.50
(D
g 2.00
1.50
1.00
0.50
0.00

 

0 50 100 150 200 250 300
Time (day)

 

 

—o—T1
—-- "12
- a- 13
—x—14

 

 

 

Figure 15: Oxygen concentration with meatballs (plastic lid, 30°C, 80% RH)

32

 

4.1.2.2 Results for C2 (23°C, 50% RH)

From Figure 16 and Figure 17, at C1, it can be seen that for T2, T3 and T4, the
oxygen concentration was rapidly reduced to nearly 0% within 1 week, and then
maintained below 0.1% during 9 months of storage. The oxygen concentration in T1 was
also reduced, but required 3 months to fall below 0.1%. Therefore, if EVOH film is used
for this kind of retort product, it is very important to control the humidity and temperature
for storage. An alternative is to use a film having oxygen and moisture barrier at high
humidity and temperature storage condition as an alternative to aluminum, which cannot

be used in a microwave.

33

 

 

Omen concentration profile with meatballs

4.50
4.00
3.50
3.00

 

-+—n
-n~m
"tum
-x-m

2. 50

g 2.00

1.50

90009)

 

 

1.00
0.50
0.00

 

0 50 100 150 200 250 300
Time (day)

 

Figure 16: Oxygen concentration with meatballs (aluminum lid, 23°C, 50% RH)

 

 

Oxygen concenration profile with meatballs
(EVOH. 23C. 50%RH)

4.50
4.00
3.50

 

 

—+—n
—a-n
nann
-*~n

a? 3.00

V

2.50
g 2.00

1.50

 

 

1.00
0.50
0.00

 

0 50 100 150 200 250 300
Time (day)

 

Figure 17: Oxygen concentration with meatballs (plastic lid, 23°C, 50% RH)

34

 

4.1.3 Discussion of permeability

The EVOH layer in multilayer film, the main gas barrier layer in the package, is
very moisture sensitive. In high relative humidity storage conditions, the overall gas
barrier (include flavor, oxygen, and so on) will be decreased. Thus, in order to achieve
sufficient barrier to maintain food fleshness, the packaging designer needs to have
knowledge about polymer material's characteristics and control parameters.
In this study, the main parameter to change the polymer permeability was temperature
and humidity. As was demonstrated by the water-packaging test, the oxygen permeability
of T1 was strongly influenced by storage conditions such as temperature and humidity
[Figure 11, 12]. T1 was filled with distilled water and sealed by an aluminum laminated
lid stock, the same as the other packages (T2, T3 and T4), in order to be able to measure
only the oxygen permeability of the trays. The barrier properties of the multilayer

structure of the tray, temperature, and humidity were expected to affect permeability

4.1.3.1 Estimating humidity of a moisture sensitive barrier layer in a multilayer structure.
As humidity increases, the oxygen permeability of EVOH is increased, but that of
PP is constant because it is a non-hydrophilic polymer.
1) Water filling packaging in C1 condition (23C, 50% RH)
Table 4 shows the composition and properties of the multilayer tray structure

which was used in the study.

35

Table 4. The structure of control tray and properties

 

 

 

 

 

 

 

 

 

 

 

 

 

Layer 1(outside) 2 3 4 5(inside)
Material PP Tie EVOH Tie PP
Thickness 0.18 - 0.025 - 0.18

WVTR 0.14 - 0.75 - 0. l4

Humidity(%) 50 - - - 100
Partial pressure P, - P2 - Pb

 

EVOH: 32 mol %
Thickness average of therrnofonned tray: mm
WVTR: ASTM F1249 (40°C, 90% RH), unit: g.mm/m2.day.atm [5]

In dealing with a moisture sensitive barrier, our final objective is to estimate the
value of the oxygen permeability coefficient, P, of the barrier layer at its water vapor
pressure p2 at its center point. Having the data that correlates P with p, the problem

becomes the estimation of p2.

£213».

Since p2 is the average of p. and p, at steady state, p2 = 2

At the steady state, the flow through the whole structure and through each layer will be

the same value. As a result, the equation for p2 will be as follows [19, 20]:

p,[l—2+2£-]+p3(21—‘+—Il—]
p _Pa+Pb_ P2 P3 P1 P2
2_ _
2 2(i+!2_+13_]
P: P2 1’:

From the upper equation, p2 can be calculated as follows:

 

 

 

 

. sol—‘33:+2-——-3‘ii)+w°-(2-3°ii+°.°3§)
p2=p" p”= ' ' ' ' =75.0%RH
2 (0.18 0.025 0.18)
2- + +
0.14 0.75 0.14

36

2) Water filling package in CZ condition (30C, 80%RH)
Through the same method, the p of water filled package in C2 can be calculated

as follows:

 

8 (0.025+2.0.18)+100.(2.0.18+0.025
p,+p,, _ 0.75 0.14 0.14 0.75

— )=90.0‘VRH
2 (0.18 0.025 0.18] °
2- + +

 

P2:

 

0.14 0.75 0.14

If the structure is symmetric so that the two outside layers were made of the same
polymer and have the same thickness, as is the case with T1, p2 is the average of p1 and
p3. When the structure is not symmetric, the value of p2 will be affected by the relative

barriers of the layers.

4.1.3.2 Estimating the permeability of a multilayer structure
1) Estimation of the permeability of PP at 30°C, 90% RH [9]

From Table 4, the oxygen permeability coefficient of PP at 30°C is 1.7x10l3
cm3.cm /cm2.s.Pa. Since PP is a non-hydrophilic polymer, PP provides a constant
permeability value at any humidity conditions.

Converting the units of PP to cc.mm/m2.day.atm, it can be calculated as follows [9]:

 

 

1.7><1'l3 [”3“ch =17, 5 lcm’llcm] x10[mm]

 

[CMZIISHPGI . ' [mzlldwllam] {cm}
=1.49E+02 zlccfl’m] (30°C,90%RH)
["1 lldayllatm]

37

2) Estimation of the permeability of PP at 23°C, 75% RH [17]

As the value of E. of PP at 30°C is 47.7 KJ/mol, the oxygen permeability of PP at
23°C can be obtained flom the value at 30°C (148.75 cc.mm/m2.day.atm).

The calculation is as follows [9, 17, 18]:

E, of PP at 30°C = 47.7 KJ/mol -:- 4.184 J = 11.401 Kcal/mol = 11401 cal/mol

= = 5738K
1.987ca1 / K .mol

 

5,, 11401cal/mol
R

l l 1 1

 

— - — = - = —7.8E - 05K"
TI T2 30+273 23+273
Ea 1 1
=ex — —-— =ex 5738x-7.8E-05 =0.64
f " RiT. 2;] p( )

P2 = P1 x f = 148.75 x 0.64 = 9.5115 + 01cc.mm/m2.day.atm (23°C, 75% RH)

3) Estimation of the oxygen permeability of EVOH at 30°C, 90% RH
The value of non-oriented EVOH (Grade: EF-F 15, EVALCA, USA) with 32
mol% ethylene between 75% to 94% RH is calculated as follows [27];
1n Y = -369.15 + 9.9697RH — 0.06062R1-I2 - (-119690 + 3232.1RH -
19.845RH2)rr
= -369.15 + 9.9697(90) — 0.06062(90)2 — {-119690 + 3232.1(90)
- l9.845(90)2] / (30 + 273)
= 2.60

Therefore, Y = 13.46 cc.(15p.m)/m2.day.atm

 

 

Converting the units:
Y=13.46 [fclnsf’m] x [Tm] =1.35E—02 Eccllmml (30°c,90% RH)
[m lldayllafm] 10 [W] [m lldayllatm]

38

4) Estimation of the oxygen permeability of EVOH at 23°C, 75% RH

The value of non-oriented EVOH with 32 mol% ethylene at 23°C, 75% RH is
also calculated as follows [27];
In Y = -369.15 + 9.9697RH — 0.06062RH2 - (-119690 + 3232.1RH — 19.845RH2)/T

= -369.15 + 9.9697(75) - 0.0606205)2 — {-119690 + 3231105) - 19.845(75)2] /
(23+ 273) = 0.13

Therefore, Y = 1.13 cc.(15um)/m2.day.atm

 

 

Converting the units:
Y=1.l3 [2061mm] x [Tm] =1.13E— 2[“][’"’"] (30°c,90% RH)
["1 lldaJ’Hatm] 10 W] ["1 lldayllatm}

4.1.3.3 Total oxygen permeability of a multilayer structure
For the overall structure, the permeability coefficient P1- is given by [17, 18]

IT
n I]

 

P, =

Thus knowing the thickness of each layer and the permeability coefficient for the

multilayer structure, we can calculate a total permeability coefficient, using the values in

Table 5.

39

Table 5. Water vapor transmission value (WVTR) of each layer in multilayer structure

 

 

 

 

 

 

 

 

 

Layer Polymer Thickness P02 (23C, 75% RH) P02 (30C, 90% RH)
1 PP 1.8E-01 9.51E+01 1.49E+02
2 EVOH 2.5E-02 1.13E-03 1.35E-02
3 PP 1.8E—01 9.51E+01 1.49E+02

 

 

0 Thickness: mm,
0 P01 and P02 : cc.mm/ m2.day.atm

1) Total oxygen permeability coefficient at 23 °C, 75% RH.

 

 

 

_ I, _ (1.8E-01+2.5E—02+1.8E—01) _ 2
PT— 3 l_i_ 1.8E-01 + 2.5E-02 +1.8E-01 —1.74E 02cc.mm/m.day.atm
M P. 9.51E+01 1.13E-03 9.51E+01

I

2) Total oxygen permeability coefficient at 30°C, 90% RH. '

 

 

 

 

_ I, _ (1.8E—01+2.5E-02+1.8E—01) _ _ 2
PT-il, " 1.8E—Ol + 2.5E-02 + 1.8E-01 ‘2'085 Olcc'mm/m'day'am
Mp, 1.49E+02 1.3515-02 1.49E+02

From the upper calculation, the total oxygen permeability coefficient at 30°C,
90% RH (1 .74E—02 cc.mm/m2.day.atm) was increased about 12 times compared to that at
23°C, 75% RH (2.08E-Olcc.mm/ m2.day.atm). This mainly resulted flom the increase of
oxygen permeability of EVOH by increased humidity and temperature flom 23 °C, 75%
RH to 30°C, 90% RH. Therefore, the oxygen permeability of moisture sensitive barrier
polymers such as EVOH is influenced largely by higher humidity conditions as well as

temperature

40

4.2 TBA

Figure 18 and Figure 19 show the trend of oxidation of the meatballs measured as
the amount of malonaldehyde as a function of the container and storage conditions;
Tables 6 and 7 show the values. For the C1 condition, one can see the meatballs in T1
were more oxidized than those in the active packages. The initial values of
malonaldehyde were assumed to be identical because the same materials were cooked at
the same conditions. Indeed, the values of malonaldehyde were not significantly different
among packages (T1~T4). However the values of malonaldehyde in active packages were
significantly lower than Tl flom 45 days. In the Cl condition, the value 0.223 for T1
after 30 days, and the value 0.286 of T1 after 60 days were similar to that of the other
containers (T2, 0.271; T3, 0.268; and T4, 0.293) after 180 days.

At the C2 condition, the value of malonaldehyde also had a similar trend to that of
C1. After 45 days, meatballs in T1 were significantly more oxidized than in the active
packages (T2, T3 and T4). Afier 180 days when the value of malondaldehyde in T1 was
0.300 mg/kg, it was about 20% lower than that in the C1 condition (0.361). The other
containers also showed similar trends. The results showed that the temperature and

humidity of the storage conditions affected the oxidation values of the retorted meatballs.

41

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Oxidiation vs. time

 

 

 

 

 

 

 

 

 

 

0.400

0.350
M
§ 0.300
<
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7.: - - a. - - 13
§ 0.150 _ ax- mm
M
E

0.100
a

0.050

0.000

50 100 150 200
The (day)
Figure 18: Trend of malonaldehyde (plastic lid, 30°C, 80% RH)
Oxidation vs. time

0.350
a. 0.300
.—. 0.250
\
*2
‘5 0.200 T1
'0
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.0 - - t - 43
g o. 100 — ex— -T4
2

0. 050
0. 000

50 100
Time (day)

150

 

200

 

Figure 19: Trend of malonaldehyde (plastic lid, 23°C, 50% RH)

 

 

 

4.3 Color

As oxidation of the meatballs and sauce affects their color, the lightness (L*
value) was regarded as an indicator of the quality of the food. Figure 20 shows optical
lightness differences between an active package (T2) and the control (T1). T1 is
significantly darker than the active package. Figure 21 and Figure 22 show the color
measurement profile for meatballs and sauce as a function of storage time for the Cl and
C2 conditions, focusing on lightness (L-value). Other measurements such as a" and b*
values were not significantly changed, so are not discussed.

For the Cl condition (30°C, 80% RH), the L-value of T1 decreased more rapidly
from 45 to 120 days and reached 35.04 at 270 days afier filling. T2 (38.10) after 270
days was similar to T3 (38.11) afier 225 days, and close to T4 (37.83) after 60 days and
T1 (37.00) afier 45 days. The result of T1 at 120 days (35.57) at C1 was close to that of
T1 (36.61) after 270 days at the C2 condition. This suggests that the L-value of the
product was affected by the temperature and humidity as well as by oxygen concentration.

At the C2 condition (23°C, 50% RH), the L“ value of the 1St test (afier 30 days) of
T1 was 40.52, but it rapidly decreased below 38.48 after 60 days and reached 36.61 at
270 days after filling. However, the meatballs in all of the active packages were superior
in lightness to those in the T1 container. T2 showed the brightest color (L* value) at both
storage conditions. T2 (39.60) after 270 days was similar to T1 (39.23) after 45 days, T3
(39.56) after 225 days and T4 (39.61) after 60 days. The results of T3 lay between T2
and T4. The result of T4 (37.84) after 270 days was similar to the result of T1 (37.74)

after 180 days. The averaged color test results are shown in Table 8 and Table 9. The

45

value of T1 , which does not contain oxygen scavenger, at C1 and C2 was generally lower

than the active packages.

46

 

Figure 20: Difference in lightness between T1 and T2 stored at C1 (30°C, 80% RH).

47

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49

 

 

L (lightness) value

 

 

 

 

 

 

 

 

 

 

 

 

 

42.00
41.00
m 40.00 T1
.31) 39.00 _ ._ _ 12
g 38.00 . . i . . ’13
l: 37.00 — ax- T4
36.00
35.00
34.00
0 50 100 150 200 250 300
storage time
Figure 21: Trend of L value (plastic lid, 30°C, 80% RH, n=4)
L (lightness) value
42.00
41.00
8 40.00 +11
:1 - I- - 12
"‘ 39.00
E - - i - - ’IB
38.00 - ax- T4
37.00
36.00

0 50 100 150 200 250 300
Storage time(day)

 

Figure 22: Trend ofL value (plastic lid, 23°C, 50% RH, 11 = 4)

 

4.4 Flavor

Shelf life results based on E-nose testing have been analyzed using Principal
Component Analysis (PCA), as shown in Figure 23. PCA is a two dimensional
representation to reduce the complexity from the data set of the e-nose sensors. Using this
analytical method, the data from the E-nose gives a more clear and visual discrimination.
The inherent structure of the data-set is preserved while its resulting variance is
maximized. PCA only describes changes in headspace volatiles during storage time.
Meatballs that were packed in active packages were compared to those in the T1
container after 9 months of storage in the Cl condition and to fresh samples. As can be
seen, the plots of T1 and those of the active packages were clearly separated. The cluster
group of T1 lies on the left bottom side of the graph, and T2, T3, and T4 are separated
from T1 and close to each other. This means that the headspace volatiles of the three
active packages are similar or close to each other. Table 10 shows numerical
discrimination values for Figure 23 to clarify its discrimination. The results indicate the
degree of difference of the samples from each package compared to fresh samples.
Therefore, a high discrimination index (DI) represents a large amount of flavor change
from the original/fresh condition. Tl showed the biggest DI index (97) compared with the
fresh group. This suggests the flavor of T1 was much more changed by oxidation after 9
months of storage than the other three groups. T2 and T3 gave the same values as each
other, 51 and 52 respectively. Through the efficiency of the oxygen scavenger, changes in
volatile profile of the meatballs were almost 50% lower than in T1. The D1 of T4 was 68,
which is a little higher value than T2 and T3, likely because the content of oxygen

scavenger in T4 was lower than in the other two active packages.

51

 

 

 

 

 

 

 

 

 

Table 10: Discrimination Index (DI) for each meatball package compared to fresh

samples

Figure 23: PCA group for meatballs afier 9 month storage

 

 

 

 

 

 

Group DI
T1 97
T2 52
T3 5 1
T4 68

 

 

52

 

 

CHAPTER 5. CONCLUSIONS AND FUTURE WORK

5.1 Conclusions

As measured by all four kinds of tests, oxygen concentration in the headspace,

TBA, color and flavor, all the active packages (T2, T3 and T4) were superior to the
passive package (T1) in extending the shelf life of food even though all packages
incorporated an MA packaging system using a C02 and N2 mixed gas-purging process on
the inside of the container after filling. The results of T2 were better than the other active
packages (T3 and T4). This means that the capacity of oxygen absorption increased in
proportion to the increase of the quantity of oxygen scavenger in the package. Actually,
the shelf life of the meatball product that was packed in a conventional passive package
does not exceed 4 months in summer storage conditions, because of unpleasant odor and
color change of the food. This study showed the possibility of shelf life extension by
using an oxygen scavenger. The oxygen level in oxygen scavenger packages maintained
a significantly lower level than that in conventional barrier packages (control). This
decreased oxidation, color changes, and flavor changes during 9 months storage. The
study showed a higher oxygen scavenger amount in the packages resulted in better
quality maintenance. T2, which contained the highest amount of oxygen scavenger
compounds, provided the best quality maintenance among the three active packages (T2,
T3, and T4). The performance difference between T2 and T3 was not significant in the
C2 condition (23 C, 50% RH). As temperature and humidity of the storage condition
increased, the oxygen concentration in the headspace of the container increased.
Therefore, in developing or designing oxygen scavenger packaging, one should consider

the proper amount of compounds in order to maintain the original quality, depending on

53

storage conditions (temperature and humidity). Manufacturing cost is also an important
consideration. The equation of Figure 13 can be used to develop this kind of new product.
EVOH or oriented nylon films, which are water sensitive polymers, may not be sufficient
as lid stock in high humidity and temperature storage conditions. Therefore, in order to
maintain food freshness under retort conditions, other oxygen barrier materials, which
have good moisture barrier, should be considered. Finally, through application of active
packaging, the extension of shelf life can be expected not only for foods, but also for

beverages and medical products.

5.2 Future work

The positive effects of oxygen scavenger systems were observed in this study.
The iron based OS system delayed oxidative degradation, color, and flavor changes. As
the next step, sensory and microbial growth evaluations are recommended to ensure the
shelf life extension by the OS system. In addition, the oxygen scavenger technology
required high relative humidity to trigger absorption because the reaction was promoted
by moisture. It is hard to apply to a low humidity condition such as a dry product.
Therefore, the first work recommended is research and development of a new OS system
that is applicable to a low humidity condition. Research on an organic based OS system
is also recommended, because iron based OS systems are difficult to apply to food

manufacturing processes using metal detectors and transparent packages.

54

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Table 17. TBA value (meatball, EVOH lid, 23°C, 50% RH)

Appendix C

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TRAY 833”" 1st 2nd 3rd 4th 5th

C2 30 Day 45 Day 60 Day 120 Day 180 Day

1A1 0.218 0.257 0.250 0.273 0.265

1A2 0.211 0.281 0.265 0.312 0.296

1B1 0.21 1 0.250 0.250 0.304 0.328

1B2 0.226 0.257 0.265 0.273 0.273

T1 2A1 0.218 0.265 0.281 0.304 0.320

2A2 0.242 0.281 0.296 0.265 0.335

281 0.234 0.250 0.265 0.273 0.296

2B2 0.226 0.242 0.296 0.289 0.328

Average 0.223 0.260 0.271 0.287 0.305

1A1 0.218 0.179 0.187 0.218 0.218

1A2 0.21 1 0.195 0.211 0.203 0.250

181 0.164 0.179 0.226 0.21 1 0.203

182 0.148 0.172 0.203 0.226 0.226

T2 2A1 0.218 0.172 0.187 0.195 0.218

2A2 0.078 0.187 0.226 ' 0.218 0.203

281 0.179 0.203 0.21 1 0.195 0.242

2B2 0.195 0.179 0.195 0.203 0.21 1

Average 0.176 0.183 0.206 0.209 0.221

1A1 0.179 0.203 0.203 0.195 0.226

1A2 0.195 0.179 0.242 0.179 0.281

1B1 0.195 0.195 0.164 0.172 0.203

1B2 0.148 0.211 0.195 0.234 0.172

T3 2A1 0.195 0.203 0.218 0.312 0.257

2A2 0.172 0.195 0.21 1 0.250 0.273

2B1 0.179 0.203 0.218 0.265 0.179

2B2 0.203 0.187 0.250 0.226 0.234

Average 0.183 0.197 0.213 0.229 0.228

1A1 0.023 0.179 0.21 1 0.242 0.21 l

1A2 0.226 0.203 0.218 0.218 0.234

181 0.21 1 0.195 0.187 0.250 0.265

1B2 0.218 0.21 1 0.21 1 0.226 0.273

T4 2A1 0.195 0.203 0.21 1 0.203 0.242

2A2 0.172 0.211 0.218 0.21 1 0.242

281 0.218 0.203 0.242 0.242 0.250

232 0.226 0.195 0.250 0.257 0.281

Average 0.186 0.200 0.218 0.231 0.250

 

61

 

 

Table 18. TBA value (meatball, EVOH lid, 30°C, 80% RH)

Appendix C( continued)

 

Sample

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TRAY NO. 1" 2nd 3rd 4th 5th

C2 30 Day 45 Day 60 Day 120 Day 180 Day

1A1 0.218 0.281 0.289 0.343 0.328

1A2 0.21 1 0.265 0.273 0.328 0.351

181 0.21 1 0.273 0.304 0.351 0.382

182 0.226 0.281 0.296 0.335 0.343

T1 2A1 0.218 0.304 0.265 0.359 0.367

2A2 0.242 0.257 0.273 0.335 0.390

281 0.234 0.265 0.281 0.265 0.343

282 0.226 0.281 0.296 0.3 82 0.382

Average 0.223 0.276 0.285 0.337 0.361

1A1 0.218 0.195 0.234 0.203 0.257

1A2 0.21 l 0.21 1 0.211 0.242 0.242

181 0.164 0.195 0.195 0.211 0.265

182 0.148 0.172 0.218 0.179 0.273

T2 2A1 0.218 0.195 0.195 0.242 0.250

2A2 0.078 0.172 0.187 0.250 0.265

281 0.179 0.203 0.226 0.218 0.250

282 0.195 0.187 0.195 0.234 0.257

Average 0.176 0.191 0.208 0.222 0.257

1A1 0.179 0.172 0.218 0.226 0.234

1A2 0.195 0.187 0.242 0.250 0.242

181 0.195 0.179 0.242 0.226 0.265

182 0.148 0.234 0.218 0.257 0.296

T3 2A1 0.195 0.179 0.234 0.242 0.304

2A2 0.172 0.218 0.226 0.21 1 0.265

281 0.179 0.242 0.234 0.226 0.281

282 0.203 0.257 0.218 0.234 0.250

Average 0.183 0.209 0.229 0.234 0.267

1A1 0.023 0.218 0.265 0.250 0.281

1A2 0.226 0.234 0.234 0.273 0.296

181 0.21 1 0.21 1 0.226 0.289 0.312

182 0.218 0.195 0.242 0.273 0.304

T4 2A1 0.195 0.179 0.226 0.257 0.281

2A2 0.172 0.218 0.242 0.242 0.273

281 0.218 0.211 0.234 0.234 0.312

282 0.226 0.187 0.25 7 0.265 0.296

Average 0.186 0.207 0.241 0.260 0.294

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Appendix E

Figure 24. Discrimination Index (DI) for T1 and fresh samples

 

 

 

 

 

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Appendix E (continued)

 

ligure 25. Discrimination Index (DI) for '12 and fresh samples

 

 

 

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66

 

Appendix 8 (continued)

 

Figure 26. Discrimination Index (DI) for T3 and fresh samples

 

 

 

 

 

 

 

 

 

67

 

Appendix E (continued)

Figure 27. Discrimination Index (DI) for T4 and fresh samples

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

68

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71

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