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30 Plastic Packagingof Frozen FoodsKwang Ho LeeKorea Food and Drug Administration, Seoul, Korea

CONTENTS

I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641

II. Types of Plastic Materials for Frozen Foods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 642

A. Polyethylene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 642

1. Low-Density Polyethylene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 642

2. High-Density Polyethylene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643

B. Ethylene Vinyl Acetate Copolymer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643

C. Polypropylene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 644

D. Polyvinyl Chloride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 645

E. Polyvinylidene Chloride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 645

F. Polyethylene Terephthalate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 645

G. Polystyrene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 646

H. Nylon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 646

III. Types of Plastic Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 648

IV. Frozen Foods Packaged With Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649

A. Frozen Meat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649

B. Frozen Poultry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649

C. Frozen Fish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649

D. Frozen Fruits and Vegetables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 650

E. Other Frozen Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 650

V. Future Trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 650

VI. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 650

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 651

I. INTRODUCTION

Freezing of foods is used to prevent the growth and activity of microorganisms in food, to retard

chemical reactions, and to prevent the action of enzymes at around2188C [1,2]. However, to main-tain frozen foods in perfect condition, packaging should provide the following protections [2]:

1. To avoid dehydration caused by moisture vapor evasion through the wall or seals of the

package. This moisture loss dehydrates surface areas of the frozen food and causes

desiccation such as freezer burn. The dehydrated surface layer can be very thin, but

may affect the appearance and ultimate quality of the product.

2. To limit oxidation promoted by enzymes not eliminated by blanching if air penetrates the

package.

3. To inhibit oxidation particularly in food with a high fat content, which can be accelerated by

light as heat can induce increased enzyme activity and chemical and bacterial deterioration.

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2006 by Taylor & Francis Group, LLC

4. To avoid flavor or volatile loss and the absorption of airborne odors which are

unlikely to occur at the same time as prepackaged foods remain frozen. Special care is

necessary with precooked foods where evaporation of the volatile content could cause

flavor loss.

5. To control physical damage caused by compression during storage and transport. Special

care should be paid in handling cases containing packs of frozen products. Further damage

may occur to the bottom layers of package if the outer containers are dropped onto a hard

surface.

Therefore, frozen food packaging materials must withstand low temperatures and sometimes

high temperatures, such as microwave and boil-in-bag products. It should be nontoxic and

convey no odors or flavors to the food. It should also provide a barrier to the transmission of

water vapor or oxygen and be water-resistant, and it should be able to be handled with machine.

Package should have the ability for graphic decoration and be tamper-resistant. Furthermore,

the package should not disintegrate when it becomes moist on thawing, and in the retail cabinet

package should be free of defects such as deterioration or collapsing.

In this chapter plastic packaging materials for frozen foods are discussed in terms of physical

and chemical properties, package types, and commercial frozen foods packaged with the plastic.

II. TYPES OF PLASTIC MATERIALS FOR FROZEN FOODS

For frozen foods, various plastic packaging materials, such as polyethylene, ethylene vinyl acetate

copolymer, polypropylene, polyvinyl chloride, polyvinylidene chloride, polyethylene terephtha-

late, polystyrene, and nylon are commercially used now and their chemical structures are shown

A. POLYETHYLENE

Polyethylene (PE) produced by coordination and radical polymerizations are mainly referred to as

low-density and high-density polyethylenes, respectively [3].

1. Low-Density Polyethylene

Low-density polyethylene (LDPE) was introduced commercially after World War II. LDPE is

made from ethylene at very high pressure (about 170 MPa) and temperature above 1508C andunder the control of free radical initiators. At these conditions, free radicals attack the double

bond and add to the monomer, leaving a free radical which repeats this addition action on more

monomer molecules.

After polymerization is complete, the pressure is reduced to atmospheric, residual raw materials

and solvents are recovered from the reactor, meanwhile, the polymer is isolated as solid particles.

These are then extruded through a die that cuts the extruded strands into pellets for shipping and

later processing.

During this procedure, many side chain branches also can be formed. These side chains hinder

crystallization and reduce key properties such as stiffness and impact toughness, however they

improve clarity and reduce density, which save the area cost of films made.

Packaging film made from LDPE for frozen foods, with a density of about 910 kg/m3 is typi-cally soft, flexible, and readily stretched. It has good clearness and provides a good barrier to moist-

ure but a poor barrier to oxygen. It gives no off-odors or flavors to foods and is readily heat-sealed to

itself. These desirable features, with its very low cost per unit area, have made LDPE one of the

most widely used plastic packaging materials. It also shows excellent cold resistance, withstanding

extreme low temperature of 2708C [4].

642 Plastic Packaging of Frozen Foods


in Figure 30.1.

2. High-Density Polyethylene

High-density polyethylene (HDPE) originally polymerized at much lower pressures if a catalyst

used to initiate polymerization of ethylene dissolved or slurried in a hydrocarbon medium.

Later, gas-phase processes were also developed. HDPE has a slightly higher density of about

940 kg/m3 than LDPE, with very little long-chain branching and a greater level of crystallinity.As a result, it is stronger in tension, stiffer, harder, and more gas-impermeable than LDPE;

however, it has reduced clarity and impact resistance resulting from its greater crystallinity.

Strength, perhaps its most important property, is a function of molecular weight.

HDPE is used for packaging films and for applications such as bottles, jars, and vials because of

the ease of converting HDPE to blow- or injection-molded containers where it is needed for greater

strength, stiffness, and lower clarity.

B. ETHYLENE VINYL ACETATE COPOLYMER

Ethylene vinyl acetate (EVA) copolymer is copolymerized vinyl acetate with ethylene, and the

resulting plastic resins are widely used as adhesives in coextrusion or to make films that have all

the desirable properties of LDPE but are much tougher. Generally up to 8% vinyl acetate

content copolymerized EVA is used for frozen foods where toughness is required [5]. Large

blocks of ice are packaged in EVA film because it can successfully resist puncturing by the

sharp corners of the block and hold the heavy weight [6].

N

N

FIGURE 30.1 Chemical structure of various polymers.

Handbook of Frozen Food Processing and Packaging 643


C. POLYPROPYLENE

When propylene molecules react to form long polymer chains at about 1.5 MPa in a hydrocarbon

solvent and without a catalyst, or in a gas-phase process, the CH3 side groups usually follow a

regular pattern, in which the polymer molecules are lined up head-to-tail, nearly parallel, and

packed together in a crystalline structure with a high degree of regularity called isotactic or syn-

diotactic. If a large number of the molecules do not follow this regular array, the polymer called

atactic is soft and sticky and is useful only as an adhesive (Figure 30.2). As a heat-seal layer in

multiple structures, polypropylene (PP) used to be copolymerized with 15% ethylene to give a

wider melting range [7].

PP, with a density of 900 kg/m3, is the lightest resin of all used for packaging. Oriented PPfilm is clearer than LDPE or HDPE, stiffer and tougher than LDPE, and has lower permeability

to moisture and gases than either, and with its higher melting point it is better suited to elevated

temperature packaging applications. This combination of properties, including a stiff feel,

resembles those of coated cellophane much more closely than does any PE film. For high gas

barrier, it can be coated with polymers such as polyvinylidene chloride (PVDC) for oxygen-

sensitive products [8].

PP film is also used in some packaging applications, such as a heat-seal layer for retort pouch or

boil-in-bag. Like HDPE, PP is stiff enough to be used in rigid containers where its superior clarity

gives it an edge over HDPE [6].

However, the major factor, which makes PP one of the most widely used clear plastic for

packaging, is temperature. It is not strong enough to resist deformation at the temperatures used

to sterilize foods in retort processing or the high temperatures used to radiant oven. Unless it is

copolymerized with a maximum ethylene content of 20%, it tends to be brittle at low temperatures

for frozen foods [4].

CH3 CH3 CH3 CH3

isotactic

CH3 CH3 CH3 CH3

syndiotactic

CH3 CH3 CH3 CH3

atactic

FIGURE 30.2 Different structures of PP.



D. POLYVINYL CHLORIDE

Polyvinyl chloride (PVC), the so-called vinyl, was introduced commercially in the late 1920s. It

is synthesized by the low-pressure free radical polymerization of vinyl chloride at temperatures in

the range of 38718C. Vinyl chloride monomer (VCM) contains a double bond that can be brokento allow head-to-tail polymerization to produce the polymer. However, various types of polymer-

ization processes can be used to make polymers for specific applications [6].

PVC is a naturally brittle material and requires the addition of large amounts of other chemical

compounds called plasticizers to make it useful as packaging film. Plasticized PVC packaging

materials are tough and clear, provide a moderate barrier to oxygen and moisture, and can be

processed to produce films, such as PP and LDPE, with good shrink properties.

However, concerns about the dangers involved in municipal incinerators have focused particu-

larly on chlorine-containing plastics such as PVC and PVDC because it is supposed that the for-

mation of dioxin, a complex chlorinated toxic molecule, is due to the inflow of these chlorinated

plastics into the incinerator [9]. Regardless of the truth of this statement, it nevertheless casts

another shadow over PVC and contributes to its growing unpopularity all over the world. It will

probably be gradually replaced in some food packaging applications by lower-cost films such as

PE, PP, or polyethylene terephthalate (PET) that can match its functional characteristics.

E. POLYVINYLIDENE CHLORIDE

PVDC is made by copolymerizing vinylidene chloride (VDC) with other comonomers such as

VCM. Although the product is normally referred to as PVDC, it is always used in the copolymer

form in packaging applications [7]. This material finds wide use in packaging because PVDC

films are clear, soft, and high barrier materials with excellent cling characteristics. PVDC coatings

can be readily applied to plastics when dissolved in solvents or dispersed as emulsions.

These coatings have the lowest permeability to oxygen at high humidity compared with any

other polymers used in large-volume food-packaging applications. Ethylene vinyl alcohol

(EVOH) can only compete with PVDC for high oxygen barrier; however, its oxygen barrier prop-

erty is very poor at high humidity due to the swelling of the polar polymer with the moisture

molecules.

F. POLYETHYLENE TEREPHTHALATE

PET is one of polyester polymers made by the condensation polymerization which are formed by

ester bonding and generating a small molecule, like water, from two different reactants, leaving

bonding sites being able for the two reactants to join together into long chains.

PET is produced under the catalytic melt polymerization of ethylene glycol and either dimethyl

terephthalate (DMT) or terephthalic acid (TPA) [7]. It is important to note that all these monomers

have two reacting groups such as22OH on the glycol,22COOH on the TPA, or22COOCH3 onDMT. This is necessary because the formation of a long chain depends on H2O or CH3OH

being split out from the both end functional groups of reacting molecules.

The clarity and the mechanical properties of PET improve dramatically when it is biaxially

oriented. This is done by stretching the film in both the longitudinal and transverse directions.

Tenter frame process is usually used for this purpose, although tubular process equipped with

biaxial orientation features can also be used. Unoriented PET, with its inferior properties, is

hardly ever used in packaging.

PET is a commercially very important food packaging material because at elevated tempera-

tures, it has excellent mechanical properties with inertness to food for reheated frozen foods. Its

excellent high-temperature properties led its early use to boil-in-bag packaging and packaging

for readymade meals where products are warmed up for consumption without removing them



from their package. The latter feature makes it one of the few plastics approved by Food and Drug

Administration (FDA) for contact with food at high temperatures.

Especially oriented PET has very excellent strength and toughness, and possesses better oxygen

barrier property, especially for fatty foods, and better CO2 barrier property than any of the common

polyolefins such as PE and PP.

A copolymer of PET with cyclohexane dimethanol, called PETG, is tough but not as clear in the

unoriented state. Despite its high cost, it is used in some thermoforming applications.

A crystallized form of PET, called CPET, is frequently used for dual-ovenable frozen

precooked dinner and entree plates that must withstand radiant oven temperatures and microwave

without deformation [6,10].

G. POLYSTYRENE

Polystyrene (PS) is made by bulk or suspension polymerization of styrene via the double bond in

the ethylene group attached to the benzene ring. Polymerization is produced at low pressure and

temperature in the range of 1202008C. PS is an amorphous, crystal clear, hard, brittle, low-strength material with a relatively low melting point of 908C and poor impact strength.However, it is readily thermoformed and injection molded but PS films have poor moisture and

gas barrier properties [6].

Copolymerization with synthetic rubber, such as polybutadiene or styrene butadiene rubber,

up to 10% by total volume improves its impact resistance, and such PS is called high-impact poly-

styrene (HIPS) [4]. HIPS is widely used for deep-draw food packaging such as egg trays, ice cream

containers, and drinking cups.

PS can be foamed by adding foaming agents such as hexane to the reaction mixture during the

suspension polymerization step. Its foamed form with 10 : 60 ratio is called expanded polystyrene

(EPS), which has a very low density but is still a rigid material that is widely used for trays for egg,

meat, poultry, and other products. It also has poor ability in conducting, providing insulation against

high and low temperature for frozen foods, and can act as heat shock absorbent [4]. The drawback

of EPS for the food packaging is its total lack of gas barrier, requiring packagers to overwraps with

barrier films when this property is required.

H. NYLON

Nylon belongs to the class of polyamide made by the condensation polymerization of an organic

acid and an amine. Nylon was the brand name for the most common of these polymers and is

now widely used as a general name for them all [6].

In packaging application, nylon 6 and nylon 6.6 are important. Nylon 6 is made by polymeriz-

ing a single monomer called caprolactam, which has both the acid group and the amino group on the

same molecule. Nylon 6.6 is made by reacting hexamethylene diamine and adipic acid to form an

organic salt by eliminating water and form the long chain polymer. Many other nylons made from

acids and amines with different structures are used for nonpackaging applications.

Nylon 6 is more common than Nylon 6.6 in food packaging, because it has a lower softening

point and wider melting range and is thus easier to heat-seal and coextrude with other thermoplastic

resins. Although its optical and mechanical properties are somewhat inferior to nylon 6.6, both

uniaxial and biaxial orientations are used to enhance the barrier and mechanical properties of

nylon 6 [11].

Nylon 6 is a clear film with pretty good gas and aroma barrier but has poor moisture barrier

properties; it also has superior strength and outstanding tear and puncture resistance at low temp-

erature. Furthermore, it maintains its mechanical properties well at elevated temperatures [7,11].

2 permeability,

and service temperature, of the above-mentioned major plastic packaging materials for frozen

foods [6,12].



Table 30.1 lists the properties, such as water vapor transmission rate (WVTR), O

TABLE 30.1Properties of Major Packaging Materials for Frozen Foods (Data Based on 25 mm Film Thickness)

HDPE LDPE EVA PP PET PVC PVDC PS Nylon

Density (kg/m3) 945967 910925 930 900 1400 12201360 16001700 1050 1140

Yield (m2/kg) 41.2 42.6 41.9 44 28.4 28 24 38 35

Tensile strength (GPa) 0.020.04 0.010.03 0.010.02 0.140.20 0.170.23 0.030.06 0.060.11 0.060.08 0.170.26

Tensile modulus

[1% secant (GPa)]

0.86 0.140.28 0.060.14 2.41 4.83 2.414.14 0.351.03 2.763.28 1.722.07

Elongation at break (%) 200600 200600 500800 50275 70130 100400 50100 230 70120

Tear strength (Graves) (kg/m) 18008900 18008900 1790026800 1790035700 18005400 40 540017900 890014300

Tear strength (Elmendorf)(kg/m) 800014000 40008000 20008000 13000 8004000 1600028000 4004000 100600 6001200

WVTR at 388C and90%RH [g/(m2 day)]

6 1631 3147 6 1623 31465 0.85 109155 155

O2 permeability at 258C and0% RH [ml/(m2 day atm)]

15503100 7750 1085013950 15502480 5090 4659300 216 31005430 1530

Haze (%) 3 510 210 3 2 12 15 1 1.5

Light transmission (%) 65 5575 80 88 90 90 92 88

Heat-seal temperature range (8C) 140150 120180 70180 90150 140180 140180 120150 120180 120180Service temperature (8C) 240120 26080 27070 240120 270150 23070 220135 26080 270200

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III. TYPES OF PLASTIC PACKAGE

For frozen food plastic packages, bags, containers, trays, and stretch wrap types are commonly used

(Figure 30.3). Bag materials vary from unsupported PE and PP films to laminates of PE, PP, PET, or

nylon. Coating the films such as PP or PET with PVDC increases the barrier properties for fatty

foods. In boil-in-bags the products are packaged in bags in which they are intended to be cooked

before opening. Foods, which produce a strong flavor during cooking, can be cooked very

conveniently.

Examples of various materials which can be used for boil-in-bag products are HDPE and PP,

which can give a reasonable shelf-life, although the packaging materials are fairly permeable to

gases. Laminated materials are used to give a longer shelf-life. More expensive materials are

PP/PE, PET/PE, PET/nylon/PP, and a laminated PP/PE or PET/PE coated with PVDC. For con-tainers, HIPS materials are used for frozen desserts and EPS trays, which look whiter and cleaner

with stretch wraps such as PVC or PE being used as alternative for paper mold product.

Thus, there is a wide range of package types available for frozen foods. However, the choice of

package types has to be made carefully, bearing in mind the cost and storage performance, and the

nature of the frozen product.

Tray and stretch wrap for fish Tray and stretch wrap for shrimp

Containers for ready-made meals Container for icecream

Bag for fruits Bag for meat

FIGURE 30.3 Various types of plastic package for frozen foods.



IV. FROZEN FOODS PACKAGED WITH PLASTICS

A. FROZEN MEAT

The spoilage of meat is reduced when the temperature falls below freezing at around 288C andbacteria and molds stop developing although some still grow at around 2108C. The physicaland chemical changes in meat take place more slowly as the temperature falls down; however,

they are not completely stopped even when stored at 2308C [1].The fat in frozen foods will eventually turn to be rancid and, if exposed to light, the red pigment

of myoglobin in the lean tissue will be fade. Irreversible dehydration will also occur at the surface

of the meat unless it is packaged in air-tight, vapor-resistant material, for example, plastic bags or

trays in conjunction with stretch wraps. Special equipment is available for this operation and the

film used must combine good water vapor resistance with an oxygen barrier. To maintain the

quality in frozen meat stored over long periods, a low temperature is essential. This must be a

minimum of 2188C, which is the normal running temperature of the domestic freezer, buttemperatures of 2258C or below, which is used for commercial cold store, is better.

Freezer burn is due to the dehydration of the surface of unpackaged or badly packaged frozen

meat. Freezer burn becomes progressively worse when badly wrapped frozen meat is stored for a

long time and grayish-white marks appear on the lean surfaces of the meat. To protect frozen meat

from rancid and freezer burn, PE bags and PVC or PVDC films are used with EPS trays [7].

B. FROZEN POULTRY

With the development of the skintight PVDC film package, prepared poultry are inserted into bags

and transferred to a rotary vacuumizing machine which packages the product with clip closures and

bag neck trimming. When shrunk, the bags form a second skin around the exact contours of the

birds, which are then either frozen in brine or in blast freezers, according to the preference of

the particular processor.

The tight vacuumized and shrunk bags protect the birds in the brine bath and prevent freezer

burn during prolonged storage. Bags are available in a variety of films and colors. Water absorption

is negligible and the function of oxygen barrier is sufficient to prevent fats from becoming rancid.

Materials used for packaging include PVDC film and a range of laminates with PE. Considerable

developments have taken place in recent years with the introduction of, for example, frozen

uncooked and precooked poultry portions [1,6].

C. FROZEN FISH

Most fish begin to freeze at about 218C and multiplication of putrefactive bacteria is stopped at298C. Although bacterial spoilage is suspended, not all bacteria are destroyed. Protection offrozen fish is needed against evaporation in cold storage caused by the transfer of moisture. This

is now usually taken care of by glazing based on dipping the frozen fish in water to ice coat the

surface or else by sealing the fish in a water and water-vapor-resistant wrapper. Thus the packed

weight of the product is maintained, visible-surface dehydration, such as freezer burn, is avoided,

and rancidity is retarded.

For packaging frozen fish, PVDC is used in vacuum-packaging some fish such as whole frozen

salmon. This system provides a better alternative to glazing process. It eliminates moisture loss on

initial freezing, drip loss on thawing, weight loss on glaze, and reduces labor and time needed for

traditional glazing. The lightly vacuumized package enables the salmon to retain its fresh charac-

teristics throughout the entire distribution system [6].

Packaging material, such as PET film, is also used for fish cakes in pillow pack style on hori-

zontal form-fill-seal machines. The film is reverse printed on the treated side and laminated

with PE. This laminate possesses barrier properties and is puncture-resistant over a wide range

of temperatures, giving protection during transportation.



D. FROZEN FRUITS AND VEGETABLES

Many fruits suffer substantial damage on freezing. Osmotic changes occur as a result of ice for-

mation that destroys the cell membrane. Generally fruits do not require blanching before freezing

and can be packaged in sugar or syrup of pureed before freezing. Vegetables, however, need to be

blanched before freezing to ensure enzyme inactivation, which would otherwise result in objection-

able flavors and loss of nutritional value and color. Most vegetables benefit from quick freezing,

which gives a crisper final product.

The majority of frozen fruits and vegetables are packaged in plastics films, such as deep

freeze grades of PE, made into pillow-type packs on vertical form-fill-seal machines. Vegetables

are packaged commonly with LDPE as moisture barriers. Larger quantities, such as one pound

or more, are packaged in EVA bags that are strong enough to carry the weight, offer the necessary

moisture barrier, have good heat-seal properties, and remain pliable at freezer temperatures. As the

contents of these larger packages are not generally consumed all at once, a reclosable feature on

the package is often used. Some soft fruits, such as raspberries, are packaged in lidded plastic

containers [1,6].

E. OTHER FROZEN PRODUCTS

One effective way to inhibit mold growth and greatly extend shelf-life for baked goods is to freeze

the product. Frozen bread is packaged in LDPE bags. For frozen desserts such as ice cream, frozen

sorbets, mousses, and puddings, thermoformed HIPS containers are often used [6,9].

V. FUTURE TRENDS

Frozen foods depend on the low temperature at which they are kept after being rapidly frozen to

preserve them in the best quality condition and their packaging is required to prevent such as dehy-

dration and oxidation of fats, which is often promoted by light, flavor, and aroma loss or gain and

physical damage during handling and transport. For this purpose, a variety of primary packaging are

currently employed including plain, coated, metallized, laminated plastic films, lidded plastic trays

and thermoforms often contained in paperboard sleeves or cartons.

However, to extend keeping times and better quality of frozen food at 225 to 2308C, itrequires the capability of withstanding these significantly lower temperatures without embrittle-

ment. In case of merchandizing transparent packaging, antifogging bags are required, which can

give an advantage to chilled foods on display, whereas frozen foods will spoil the transparency

due to deposits of frost, because of the below-zero temperatures.

The development of ready meals for microwave is not so easy as might be supposed because

different meal components require different times for heating unless their processing has taken

account of this. The use of susceptors to provide browning and crisping of pizza or fish

stick cases has received much attention and is a field that has still to be developed further.

Much emphasis will also be placed on environmental protections. Considerations should be

given during the design and development of plastic packaging for frozen foods for the best packa-

ging material to meet not only the protective needs of the food, but also environmental protections

in terms of material resources, energy conservation, and most importantly, recyclability, which will

result in minimizing the growing landfill problem [2,9,13,14].

VI. CONCLUSIONS

Plastic packaging materials, such as PE, PP, PET, PS, and nylon, are widely used for frozen foods.

These packaging materials should have proper barrier properties such as moisture vapor, oxygen,



and flavor or volatile compounds and impact strength and puncture resistant to be used at low temp-

erature, while keeping acceptable food quality of frozen products during processing, storage, and

handling of the foods.

Frozen meat, poultry, fish, fruits and vegetables, and desserts such as ice cream are some of

frozen products commonly packaged with plastics. In the future, plastic packaging materials will

be developed to meet not only functional protective needs of foods, but also material resources,

energy conservations, and especially recyclability to handle waste management for environmental

protection.

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Table of ContentsChapter 30: Plastic Packaging of Frozen FoodsCONTENTSI. INTRODUCTIONII. TYPES OF PLASTIC MATERIALS FOR FROZEN FOODSA. POLYETHYLENE1. Low-Density Polyethylene2. High-Density Polyethylene

B. ETHYLENE VINYL ACETATE COPOLYMERC. POLYPROPYLENED. POLYVINYL CHLORIDEE. POLYVINYLIDENE CHLORIDEF. POLYETHYLENE TEREPHTHALATEG. POLYSTYRENEH. NYLON

III. TYPES OF PLASTIC PACKAGEIV. FROZEN FOODS PACKAGED WITH PLASTICSA. FROZEN MEATB. FROZEN POULTRYC. FROZEN FISHD. FROZEN FRUITS AND VEGETABLESE. OTHER FROZEN PRODUCTS

V. FUTURE TRENDSVI. CONCLUSIONSREFERENCES

dk3876ch30

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