Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

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Packaging materials should provide the following

properties:

0014 high hygiene standards;

0015 sufficient mechanical strength and internal bond;

0016 liquid proofness;

0017 interness to product;

0018 light barrier;

0019 low gas permeability;

0020 seal ability;

0021 machinability in converting and filling processes.

Canning

0059 The process of canning is sometimes called steriliza-

tion because the heat treatment of the food eliminates

all microorganisms that can spoil the food and those

that are harmful to humans, including directly patho-

genic bacteria and those that produce lethal toxins.

Most commercial canning operations are based on the

principle that bacteria destruction increases tenfold

for each 10



C (18



F) increase in temperature. Food

exposed to high temperatures for only minutes or

seconds retains more of its natural flavor. Recent de-

velopments include the use of cans made of aluminum,

very thin steel, and coated and uncoated plastic. Can

openers are unnecessary for cans that have a pullable

metal tab or ring attached at the top. Despite the

widespread popularity of canned foods, the major

limitation of canning is in the quality of the final

product. Since food is not a good conductor of heat,

excess heat needs to be applied to the container’s sur-

face for a period of time to guarantee sufficient heat at

the center, or ‘cold spot,’ in order to destroy all organ-

isms causing spoilage and disease. This method of

preserving causes foods to lose juices, texture, flavor,

and nutrients. The retort pouch, developed in the

1970s to alleviate this problem, is a 3-layered laminate

with flexible plastic films as the outer and inner layers

and aluminum foil in the middle. The pouch, which is

approximately 19 mm (0.75 in) thick, is filled and

sealed under vacuum. Because the pouch has a large

surface-to-volume ratio, heat needs to penetrate less

than 10 mm (0.38 in) from the surface to the ‘cold

spot,’ thereby yielding greatly improved products.

Selection Criteria for Packaging Materials

0022 Some of the important packaging considerations,

which influence the choice of packaging materials,

are given below.

Product Protection

0023 The choice of packaging material has to be made

depending upon the nature of the product, i.e.,

susceptibility of the ingredients used to undergo de-

terioration in contact with water, moisture, gases,

light, etc. For products containing high fats, the pack-

aging material must have high oxygen barrier proper-

ties. For such applications, material based on nylon,

nitrile, or polyester may be considered. However, for

products that are likely to deteriorate only by mois-

ture gain or loss, a packaging material with sufficient

moisture barrier properties may be adequate. For

light-sensitive products, an opaque packaging mater-

ial may be necessary. The shelf-life is another import-

ant criterion that influences packaging material

specifications.

Convenience

0024The convenience for consumers and amenability of

the packaging material to provide such features is

a predominant factor in the final choice. Features

such as reclosability, dispensing capability, stand-up

facility, etc. are some examples of packages preferred

by the end users.

Sales Appeal and Package Decoration

0025For some products, it may be necessary for the pack-

age to communicate effectively and visually attract

the consumer while it is displayed on the shelf. Thus,

the choice of packaging material is influenced by such

properties as gloss, transparency, and ability to accept

multicolor printing.

Product Package Compatibility

0026This aspect is critical, particularly for edible products.

Product package compatibility testing is carried out

to assess the possibility of any migration from and to

the product. Any loss of product flavor or product

tainting with unacceptable odor is also checked.

Packaging Machinery

0027For products that are mass-produced, the speed of

packaging is very important, and the packaging ma-

terial chosen must run smoothly on the packaging

machine used. Here, the mechanical properties of

the films and laminates such as tensile strength, rigid-

ity, coefficient of friction, slip properties of the film

and laminates, and their susceptibility to develop a

static charge need to be considered.

Package Sealing Efficiency

0028However good a packaging material may be for a

given product, its ability to protect the product is

determined by its seal strength. Often, the product

is spilled around the sealing area while filling. In such

cases, sealing of the package with product contamin-

ation on the sealing surface is necessary.

PACKAGING/Packaging of Liquids 4305

Package Strength

0029 Product distribution over longer distances invariably

involves multiple handling and long storage periods.

These are generally associated with both mechanical

and climatic hazards. The choice of material, there-

fore, has to be made, based on the severity of hazards

and the capacity of the material to withstand these in

a given distribution situation.

Statutory Requirements

0030 Often, there are certain regulations governing the

choice of packaging material, for example, in the

packaging of pesticides.

Material Availability

0031 Any user would like to have multiple sources of pro-

curing their packaging material. Therefore, the

sources of supply and the availability of material

become predominant considerations.

Cost

0032 Sometimes, marketing success depends on how low

the product is priced. The ultimate choice of pack-

aging material is often influenced by the cost at which

the functions indicated above are achieved.

0033 The criteria discussed above are some of the more

important considerations. Depending upon the type

of product and the market, many additional consider-

ations may become important. However, by and

large, if the above criteria are used while selecting

the packaging material, the user is likely to arrive at

an optimum choice of packaging material.

Developments in Packaging of Liquid

Foods

0034 Liquid food products have been packed, preserved,

and transported over the ages by a variety of methods.

Wooden containers, earthen pots (glazed pottery or

jars), and glass continue to be the major materials,

even in the present day. All these had the benefits of

being nonreactive to the food material and also

efficient to contain the material resisting deformation

besides being leak-proof (if properly closed). Over the

years, with man’s quest for newer technologies,

packaging of liquid food products also gained greater

importance. The need for developing alternative

materials and methods for liquid food packaging

has arisen for several reasons, such as to reduce the

cost of packaging, improve the shelf-life, provide

convenience in using the product, improve the hand-

ling during transport or in retail outlets, and also

promote consumer acceptance of the product. It was

further necessitated due to changed distribution

systems, competition, changing consumer needs, and

availability of new packaging materials and/or

methods.

0035For transporting in bulk, liquid material can be

carried in wooden drums or metal drums. Alterna-

tively, containers can be packed in wooden crated,

or fiber mold cases, e.g., glass carboys in crates, poly-

thene, or synthetic plastic carboys can be considered.

A new development in this area is the bag-in-box type

of packaging for liquids. In examining the shelf-life

requirements of the product, microbial spoilage in the

case of fresh food products such as milk and fruit

juices, due to their high susceptibility to microbial

contamination and hence requirement for steriliza-

tion/pasteurization, needs to be considered. Pack-

aging material should withstand rigorous treatments

during such packaging stages.

0036As the industry grows, and the demand for con-

venience increases, the need for quality packaging

undoubtedly increases. Today, packaging is cost-

effective in the sense that the package is pivotal to the

marketing philosophy of the urban markets offering a

wide choice at a low cost. Thus, the model food

package has to keep down marketing costs and offer

the consumer tangible price benefit. The increased

speeds on machine lines and use of flexible laminates

in place of tin containers may be considered as a

development.

0037As outlined above, the selection of the packaging

material and the packaging machines depends upon

the food to be packed, and the methods together

can be called as a packaging system. Today, fruit

juices, wines, water, oil, soup, concentrated vege-

table, pure

es, etc. are packed in a variety of systems

such as prepac, Blockpak, Zupack, Purepak, Ceka,

Tetrapak, thermoforming systems, and bag-in-box

systems. Facilities such as asceptic packaging, hot

filling, nitrogen flushing, etc. for the product are

also available.

0038There are the range of cartoning systems and form–

fill–seal machines now available and are replacing the

glass and tin containers for liquid food packaging.

Among these, asceptic packaging is yet another

development.

0039Requirements with respect to hygiene and imper-

meability are stringent for liquid food products.

Sealing must be tight. There are basically three types

of machines for the packaging of liquids, viz. vertical

form–fill–seal machines horizontal form–fill–seal

machines and sachet-forming machines.

0040All the types can be used for liquid food product

packaging. They can have such secondary facilities

as gas flushing, vacuum zing, etc. introduced. Standi-

packs and gusseted sachet packs are quite acceptable

for liquid food products for consumer convenience.

4306 PACKAGING/Packaging of Liquids

Resources and Energy

0041 Presently, one-way carton packages for milk, juices,

and other noncarbonated beverages coexist with one-

way and returnable alternatives like the glass or plas-

tic bottle. At first sight, the returnable alternatives

seem preferable from an energy and ecological point

of view. But considering the entire process, from ex-

traction of raw materials, through production and

distribution to the handling of waste, this is not the

case when compared to one-trip cartons. Investiga-

tions show that there are only minor differences,

ecologically speaking, between a returnable bottle

with a realistic trippage for modern retailing and a

plastic-coated paper bottle.

0042 The constituent materials of the dominant pack-

ages for the noncarbonated liquid foods, for glass

bottles, cans, plastic bottles, and cartons, differ in

practically every aspect: raw material consumption,

energy consumption, impact on water and air, and

amount and quality of waste. The overall energy

requirements for the different packages are of the

same magnitude (Figure 2), water and air pollutants

are comparable, and a large amount of waste is

generated in the use of returnable bottles if a bottle

does fewer than 20 trips.

0043Carton-based packages using wood as the basic

raw material exploit a renewable resource. Present

planting of trees exceeds harvesting, so there will

not be any deforestation as a result of the manufac-

ture of paper containers.

0044Litter and waste may be regarded as minor prob-

lems as far as PE-coated cartons are concerned. If a

plastic-coated cartonboard is left in nature, complete

degradation will usually take several years, the main

problem being the degradation of the polymer.

Biodegradable PE has been discussed as an alternative

outer coating. Although this solution would increase

the rate of degradation considerably, it has never

found applications. The waste problem is the more

important issue when it comes to disposabilities.

Nevertheless, the waste from PE-coated cartons is

easily handled, does not require separate collection,

and may be used as a source of energy when

incinerating.

Marketing Aspects and Competition

0045The main alternatives in liquid food packaging are

glass and plastic bottles, cans, and plastic-coated

cartons. A packaging system based on cartons is

facilitated by low overall costs. In fact, the one-way

1.5

1.0

0.67

kWh/I

0.49

0.5

0.0

(a)

A. Carton Returnable glass bottle

5 10 15 20 25 30 trips

Energy recovered

Energy in material and packaging

Energy in filling and distribution

0.43

0.22

1.5

1.0

0.70

0.72

kWh/I

0.49

0.5

0.0

(b)

A. Carton Returnable glass bottle

5 10 15 20 25 30 trips

0.56

0.09

0.45

0.09

0.53

0.22

fig0002 Figure 2 Comparison of energy counts for milk (a) and juice (b) packaged in cartons and returnable glass bottles. A

and A

represent the energy counts for cartons including and excluding wood energy, respectively. The figures are reproduced from data

given in Sundstrom G (1982) Milk Packages and Energy. Malmo, Sweden: Sundstrom AB and Sundstrom G and Lundholm MF (1982)

Juice Packages and Energy. Malmo, Sweden: Sundstrom AB.

PACKAGING/Packaging of Liquids 4307

carton container is found to be a cheaper alternative

than cans and returnable glass bottles. The profitabil-

ity is largely due to low distribution costs, storage

efficiency, maximum use of shelf-space, and low

labor costs.

0046 For the working environment, systems based on

one-way cartons are regarded as superior. Different

products with very different processing qualities can

be handled, including mineral water, nectars or fruit

juices with a high pulp content, wine, milk, preserved

dairy products, and others.

0047 In modern retailing, the package serves the purpose

of being an important source of information. Being

printable and having four sides available for commer-

cials and content declaration, the carton is its own

sale promoter, offering free advertisement displayed

on shelves and the consumer’s table.

0048 In Western European countries, milk represented

somewhat below 80% of liquid carton demand at the

beginning of the 1980s, and presently the cartons

hold about 60% of the total milk market. There is

currently a decline in the total milk market but an

increased consumption of cartons for milk, thought

to be due to the commercialization of long-life milk

and the replacement of returnable bottles in the UK.

Cartons have achieved a high penetration of the milk

market in most Western countries, so the scope for

further progress may be regarded as limited outside

the UK. Furthermore, fresh milk (i.e., pasteurized

milk) is believed to appeal to popular taste more

than sterilized milk, and the market may well turn

in favor of fresh milk where proper refrigeration

conditions may be achieved.

0049 The second largest product group is for fruit juices,

holding about 15% and steadily increasing, and the

third largest product group is soft drinks, holding

about 5%. Other products for which the cartons are

likely to increase in importance are wine, mineral

water, vegetable oil, and juices.

Overview

0050 Liquid food packaging has been vital in assuring man

of a year-round supply of a variety of foods and has

changed us from an agrarian to a cosmopolitan

culture.

0051 Significant changes have taken place over the last

three decades, and packaging is becoming recognized

as a definable and essential technology. It is

considered earlier in the food product development

cycle and a more organized approach to actual pack-

age development is taken.

0052 Currently, package designs are first tested under

laboratory conditions (vibration, drop tests, in-

clined impact) and then confirmed by actual field

use, sometimes with little agreement. Improvements

in agreement between field experience and laboratory

testing will be improved by such developments such

as:

0053Shipping hazards recorders, such as that de-

veloped by the US Army Natick Development

Center (Figure 3), to measure and record on tape

such events as number and height of drops and

environmental conditions such as temperature and

relative humidity.

0054In estimating shelf-lives, recognition of diurnal

temperature and humidity changes, and the un-

steady state nature of oxygen and water vapor

permeabilities.

0055In devising more relevant tests to replace archaic

techniques, such as the Muller burst test for fiber-

board.

0056Computers can be of great help in the statistical

evaluation of the massive environmental and hazards

data required, defining any distribution system suffi-

ciently to permit trade-off decisions on product loss

versus packaging cost. This will also be essential in

handling laboratory test data and will be useful in the

graphic mode, for actual package design.

0057On-line, nondestructive test procedures such as

the infrared seal defect technique, the sonic vacuum

test technique for cans, and magnetic metal contam-

ination detection procedures will be more plentiful.

Energy costs will govern package design to a great

degree and will necessitate frequent substitutions for

critical materials.

0058There will be greater emphasis on the nonprotec-

tive functions of a packaging system. The flexible

100

120

30 40 50 60 70

Drop height (5 cm increments)

Number of drops

80 90 100 110 120

fig0003Figure 3 Frequency histogram of recorded drops. Distribution

of 312 recorded drops in 5-cm increments. The system activation

threshold enables drops of less than 15 cm to be recorded. This

represents 1500 days and 80 000 km of shipments. From Barca FD

(1975) Acquisition of Drop Height Data during Package Handling Op-

erations. Natick, MA: Aeromechanical Engineering Laboratory,

US Army Natick Development Center.

4308 PACKAGING/Packaging of Liquids

packaging system for thermoprocessed foods extends

the boil-in-bag heating capability to nonrefrigerated

foods. Untended vending systems using microwave

energy for in-package product heating appear to be

feasible. Liquid foods are being studied with the aim

to use the flat configuration to achieve a high product

quality and container designs for heating for serving

and serving from the container itself.

See also: Milk: Liquid Milk for the Consumer; Processing

of Liquid Milk; Pasteurization: Pasteurization of Liquid

Products

Further Reading

Athalye AS (1992) Packaging as a system. In: Plastics in

Packaging, pp. 15–17. New Delhi: Tata McGraw –

Hills.

Barca FD (1975) Acquisition of Drop Height Data during

Package Handling Operations. Natick, MA: Aero-

mechanical Engineering Laboratory, US Army Natick

Development Center.

Goyal GK (1991) Practice and research related to pack-

aging of indigenous dairy products – A review. Journal

of Indian Dairyman 43(11): 489.

Gupta TR (2000) Bulk asceptic packaging of fruit pulp

and concentrate. 14th Indian Convention of Food

Scientists and Technologists Souvenir, pp. 78. Mysore,

India: Central Food Technological Research Institute.

Iversen A (1987) Cartons for liquids. In: Modern Pro-

cessing, Packaging and Distribution Systems for Food,

pp. 86–90, 105–107. Westport, CT: AVI.

Kumar KR (2000) Global standards for food packaging.

14th Indian Convention of Food Scientists and Tech-

nologists Souvenir, pp. 26–32. Mysore, India: Central

Food Technological Research Institute.

Lampi RA (1978) Packaging of food – Overview. In:

Encyclopedia of Food Technology and Food Science

Series, vol. 3, pp. 591–597. Westport, CT: AVI.

Menon CPS (1986) Developments in packaging of liquid

foods. In: Packaging of Food Products, pp. 187–192.

Bombay: Indian Institute of Packaging.

Narayanan CK (2000) Trends in health food drinks pack-

aging. 14th Indian Convention of Food Scientists and

Technologists Souvenir, pp. 78. Mysore, India: Central

Food Technological Research Institute.

Nunn DW (1980) Alternative packaging of milk – a conse-

quence analysis. CMI Report No. 790306–1. Fantoft,

Norway: Chr. Michelsens Institute.

Raj Baldev (2001) Food and packaging interaction – migra-

tion concepts and regulations. Indian Food Industry

20(5): 67–74.

Rangarao GCP (2001) Computer simulation of packaging

and storage environments and prediction of shelf life of

moisture sensitive foods. Indian Food Industry 20(6):

65–70.

Sarkar PC and Gupta PC (2002) Shellac-based tin can

lacquers for the packaging industry. Indian Food Packer

56(2): 69–71.

Sogi DS, Shergill RS and Bawa AS (2000) Effect of pack-

aging materials on storage of lemon juice beverage con-

centrate. Journal of Food Science and Technology 37(3):

296–299.

Sundstrom G (1982) Milk Packages and Energy. Malmo,

Sweden: Sundstrom AB.

Sundstrom G and Lundholm MP (1982) Juice Packages and

Energy. Malmo, Sweden: Sundstrom AB.

Sundstrom G and Lundholm MP (1985) Resource and

Environmental Impact of Tetra Brik Aseptic Carton

and of Refillable and Nonrefillable Glass Bottles.

Malmo, Sweden: Sundstrom AB.

Packaging of Solids

M Mathlouthi, Universite

de Reims

Champagne-Ardenne, Reims Cedex, France

Background

0001The aim of packaging solid foods is to protect

them against spoilage and to preserve their quality.

Selecting a suitable packaging system for this category

of products requires a good knowledge not only of the

factors affecting their stability but also of the extent to

which they are deformed when submitted to mechan-

ical constraints. Both stability and resistance to being

deformed are influenced by the water content and

water activity (a

). Most of the physical, biochemical,

and microbiological changes of solid foods also

depend on a

. Also, lipid oxidation and other causes

of decrease in quality originating from the permeation

of gases, water vapor, aroma substances, and other

chemicals, or the transfer of energy (light, heat) to an

acceptor phase (moisture, fat, etc.) in the product must

be minimized through the choice of packaging

material, which should be a barrier to matter and or

energy transfer. Such a barrier should not be com-

pletely tight to take into account a possible release of

water vapor from the product in the inner space of the

package, which might increase the relative humidity to

a limit value of a

for which the caking of powdery

solid foods can occur. In addition, as solid foods are

stored and distributed in their packages, one of the

objectives of packaging, besides the protection of

the product, is to meet the requirements for successful

marketing. (See Oxidation of Food Components;

Water Activity: Effect on Food Stability.)

Classification

0002This classification of solid foods is based on the

degree to which they are deformed when submitted

PACKAGING/Packaging of Solids 4309

to compression or agglomerated and compacted as a

result of moisture increase. This depends on whether

they are soft, rigid, or powdery products, and may

influence the protectivity of the packaging material as

well as its acceptance by the consumer. A special class

is devoted to food powders for which flowability,

density, morphology of particles, and their crystallin-

ity play a major part. Three categories of products are

distinguished:

0003 nondeformable solid foods like toasts, biscuits,

crackers, hard cheeses, confectionery, chocolates,

etc.;

0004 deformable products like sandwich loafs, industrial

pastry, soft cheeses, meat, and meat products, etc.;

0005 food powders like refined granulated sugar, wheat

flour, spray-dried milk, dairy-based infant formula

powders, etc.

0006 The choice of packaging solution depends on the

objective sought, namely the nonperception by the

consumer of any degradation of the product. As with

heat treatment, absolute protection of a packaged

foodstuff against alteration is not possible. Thus,

protection in this context is only a commercial notion

comparable to that of commercial sterilization. It was

decided to classify solid foods into deformable and

nondeformable products in order to discriminate be-

tween those products (deformable) for which the main

origin of degradation is the barrier characteristic of

the packaging material. In the case of deformation, the

appearance of the product becomes the dominant cri-

terion as regards acceptability by the consumer. For

nondeformable solid foods, the product may be the

origin of a change in structure of the packaging mater-

ial, leading to a reduction of thickness, pinholes or

tears, which modify the transfer of matter or radi-

ation, and provoke biochemical alterations, reduction

in shelf-life and, finally, rejection by the consumer. For

solid foods, much more than for liquid foods, the

concept of an efficient packaging system should be

based on the interaction between the product, the

packaging material, and the machinery involved.

0007 To generalize for solid foods as a whole, baked

goods are taken as a model for this class of food prod-

ucts. Indeed, it is easy to find among baked goods

representation examples on nondeformable products

like toasts, biscuits, or crackers, and on deformable

products like bread or sponge cake. For these prod-

ucts, as for the majority of solid foods, a good criter-

ion of differentiation is the a

. For rigid baked goods,

the a

is low, about 0.05–0.30, and its value for soft

products is around 0.70–0.96. Besides acting as a

good reference mark for the aptitude for deforming

on which we base our classification, the a

is associ-

ated with most alterations that occur in solid foods.

0008As a representative product of food powders, white

sugar can be taken as an example. Besides the sensi-

tivity to moisture and temperature, the stability of

packaged sugar, either granulated or cubes, depends

on the stability of crystallization at the surface of the

crystals, absence of amorphous or fine particles, and

the minimization of the fraction of water content

called ‘free’ water or solvent water on the water

vapor sorption curve.

Causes of Alterations

0009Changes in packaged solid foodstuffs are perceived as

being due to a mass or energy transfer across the

package providing that there exists a donor (environ-

ment, packaging material, etc.) and an acceptor

(mobile phase of the solid food). This approach may

seem to be complicated, but it has the advantage of

relying on classical equations of diffusion. The re-

quired characteristics of the packaging material are

approached in a dynamic way and deduced from

mathematical models of the prediction of shelf-life.

0010Instead of reviewing all possible matter and energy

transfers and their effects on the degradation of solid

foods, three major causes of alterations are described:

the transfer of water vapor, the transfer of radiation

(light), and the transfer of chemicals during storage.

Quality Changes originating from the

Transfer of Water Vapor

Nondeformable Products

0011For this category of foods, an increase in a

is gener-

ally the origin of the alteration and leads to a loss of

crispness. However, an increase in moisture may be

protective against lipid oxidation in low-moisture

foods. In most cases, there remains in the headspace,

after sealing the container, enough oxygen to initiate

oxidation where an acceptor, e.g., ethylenic bonds in

unsaturated fatty acids, exists. It may be noted that,

in rigid baked goods with an a

of 0.30, the risks

of biochemical or microbiological alterations are

absent.

Deformable Products

0012It may be recalled that the a

for these foods is > 0.70,

which corresponds to an increase in availability of

degradation reaction sites due to an enhanced mobil-

ity of water. The risks, in this case, are due to water

vapor transfer (gain or loss of weight), chemical and

enzymatic reactions, and microbial spoilage. It is also

observed that, in this zone of a

values, a structural

rearrangement of one of the constituents (starch) of

the product may lead to an alteration known as

4310 PACKAGING/Packaging of Solids

staling of the baked goods. (See Spoilage: Chemical

and Enzymatic Spoilage; Bacterial Spoilage.)

0013 The kinetics of alteration reactions depend on the

components of food. This is the case, for example, for

the oxidation of lipids. If fats are sequestered by the

starchy phase, as in a dry cake (sable

), lipid oxidation

does not occur, and the shelf-life of the cake is pro-

longed. If lipids are also on the surface of the product,

as with extruded snacks, lipid oxidation becomes a

limiting factor in the quality assurance of packaged

solid foods. The availability of water for enzymatic

reactions or microbial growth may be limited by the

addition of a

depressors, ‘humectants’ like sugars,

polyols, glycerol, or proteins. To minimize nonenzy-

matic browning, it is important to reduce the dur-

ation of exposure to water vapor pressure at the

optimum value (a

¼0.65–0.75) for the Maillard

reaction. However, at least for baked goods, the

appearance of the product, which is appreciated by

the consumer, is partly due to the Maillard reaction.

(See Browning: Nonenzymatic.)

Food Powders

0014 Caking is the major alteration of free-flowing food

powders ingredients and results in the transformation

of a pulverulent product into lumps, then into ag-

glomerated solid, and finally into a sticky material

that has lost its functionality. Such a transformation

depends on the temperature and moisture content.

Different stages are involved amid which are the

bridging of particles, their compaction, and liquefac-

tion. For sugar crystals, the dynamic evolution of a

and its increase to reach 0.80 can provoke the agglom-

eration of particles, especially when fine crystals with

an average size less than 250 mm are present. When

the amount of fine particles increases (above 10%) the

value for caking is lowered to around 0.45.

0015 Another origin of instability of food powders is

their amorphous structure, which allows their exist-

ence below the glass transition temperature (T

)inan

out-of-equilibrium state. It is possible to reach T

normal temperatures if the relative humidity is in-

creased. This might be at the origin of a situation

where the viscosity is decreased at such a value that

allows the product to be transformed into a rubbery

material, which sticks to the package and loses its

quality.

Alterations Originating from Exposure to

Light

0016 Radiation, particularly of ultraviolet light, has a cata-

lytic effect on the quality changes in foods. Deteriora-

tive changes like the destruction of lipid-soluble

vitamins, the loss of riboflavin and other vitamins,

and changes in proteins and food pigments are accel-

erated by light. The presence of oxygen is intimately

linked to these light catalyzed reactions.

0017These alterations lead to rancid foods with a

changed color and reduced nutritive value. The odor

and color changes of the product are obviously per-

ceived by the consumer. In order to limit the rate of

light-induced deteriorative reactions, the choice of

packaging material for solid nondeformable foods

should insure a low oxygen partial pressure and a

nontransparent package.

Alterations Originating from Food–

Package Interactions

0018For this group of alterations, the notion of reciprocal

mobility of a donor and a receptor acquires all its

importance. Indeed, whatever the migration (from

the product to the packaging material or from the

package to the food), it is essential to have a carrier

for the transfer of the migrant chemical. It is also

necessary to distinguish between hydrophilic and

lipophilic chemicals. For nondeformable products

0.30), the migration of some constituents of

the packaging material (low-molecular-weight poly-

olefins, plasticizers, lubricants, etc.) into the mobile

fatty phase of the food may be observed. Likewise,

the adsorption of fats by the material (polyethylene,

polypropylene, etc.) in contact with solid foods may

occur.

0019For deformable products (a

0.70), the prepon-

derant mobile phase is water, and only hydrophilic

chemicals are implicated in migration, i.e., acrylic

derivatives of varnish, glycol derivatives, urea, for-

maldehyde, etc. In this category of deformable

foods, it may be that both the aqueous and fatty

phases are mobile, as in some sponge cakes, and

both migrations are then observed. The structure

and composition of the product help to determine

the preponderant mobile phase in contact with the

packaging material. Although fat may be fixed to

starch and water immobilized by ‘humectants,’ this

category of solid foods is more difficult to control in

terms of migration.

0020Stains of syrup are sometimes observed at the top

of paper board package of sugar lumps. This is ob-

served when the lumps are packed at a high tempera-

ture (above 40



C) and not cured in a ventilated room.

Such conditions (40



C and relative humidity above

85%) lead to the diffusion of sucrose in the film of

syrup surrounding the crystals. After crystallization

of sugar in the film of syrup, and the release of hydra-

tion water, the syrup becomes sufficiently mobile to

stick to the package. As granulated sugar may act as

PACKAGING/Packaging of Solids 4311

an adsorption medium, odors from the environment

or other volatiles from the packaging material may be

temporarily adsorbed by the sugar.

Preservation

002 1 In order to protect a solid food against alteration, it is

necessary to place a barrier between it and the envir-

onment. This barrier should be adapted to the cap-

acity of adsorption of the food for the factors

responsible for the deteriorative reactions. The bar-

rier properties of the packaging material are deter-

mined by its permeability to the degradation agents,

mainly gas or vapor permeating from outside.

Permeability of Packaging Material

002 2 The mass transfer of oxygen, carbon dioxide, water

vapor or aroma components, or heat or radiant

energy (ultraviolet, infrared, b, g or microwave radi-

ation) across the packaging material is generally ruled

by a relation derived from Fourier or Fick’s laws. In

the case of unidirectional transfer, under a steady

state and at equilibrium, the quantity of permeated

material per unit of time (Q) is given by a Fick’s first

law-type equation:

Q ¼PA

p

, ð1Þ

where P is the permeability, A is the active surface

area of the packaging material, Dp is the difference in

pressure (or concentration) on either side of pack-

aging material, and l is its thickness.

002 3 The permeability coefficient, P, is a function of the

number of variables, which include the structure of

the packaging film, the properties of the permeate,

the time, the pressure, and the thickness (the tempera-

ture is constant). Depending on the sensitivity of the

product to water vapor, oxygen, or loss of aroma

components, the packaging material composition

and barrier characteristics are determined (see

Tables 1 and 2).

Prediction of Shelf-life

002 4 The classification of solid foods determines the choice

of the model transfer equation and affects the predic-

tion of the deteriorative reaction rate. (See Storage

Stability: Shelf-life Testing.)

0025 For nondeformable foods, the most critical transfer

is that of water vapor and/or oxygen. The kinetics of

oxidative degradation should be adapted to each

category of product, while the model equation used

for water vapor transfer may be generalized.

0026For deformable foods with a

> 0.70, water vapor

transfer generally occurs from the inside to the out-

side of the package and is the preponderant factor of

alteration. In some cases, more than one transfer has

to be taken into account, for instance, water vapor

and oxygen. The mathematical model of mass trans-

fer is then obviously more complicated.

0027In order to calculate the shelf-life of products sen-

sitive to moisture, eqn (2) is applied:

¼

PA ðp

 p

, ð2Þ

where dW/dt is the flow of moisture, and p

and p

are, respectively, the water vapor pressure in the ex-

terior and the interior of the package. If storage takes

place at a constant temperature, p

and p

may be

replaced by a

w,e

and a

w,i

, the values of outer and

inner water activities, and eqn (2) can be written in

integral form as:

t ¼ K

degradation

origin

f ðaw Þdaw, ð3Þ

where t is the shelf-life of the product, and K is a

constant related to the properties of the product, the

permeability of the packaging material, and the con-

ditions of storage. Eqn (3) is only valid when the

degradation originates from a change in a

due to

moisture transfer. In the case of oxidative deterior-

ation, two equations are applied, one accounting for

oxygen transfer and the other for its adsorption by

food. For transfer, the relation is:

dðO

¼ P

P

, ð4Þ

where d(O

)/dt is the flow of oxygen into the package,

is the permeability, A is the surface of permeation,

Dp is the pressure difference of oxygen between the

interior and exterior of the package, m

is the absorp-

tion capacity of food, and l, as before, is the thickness

of the packaging film. It is generally supposed that

oxygen is adsorbed by food, and the rate of adsorption

of oxygen d(O

)/dt is given by:

dðO

þ k

ð5Þ

where P

is the partial pressure of oxygen, and k

and k

are two constants related to the degree to

which the food adsorbs oxygen. An increase in the

rate of adsorption of oxygen provokes an increase of

oxidation. However, many other factors affect this

type of degradation (light, heavy metals, water activ-

ity, etc.), and it is difficult to find mathematical model

accounting for shelf-life as regards oxidation.

4312 PACKAGING/Packaging of Solids

0028 Other degradations may be predicted from math-

ematical models, like nonenzymatic browning on

model systems (reducing sugars þamino acid) in the

range 0.55–0.85, but a precise prediction of a real

degradation in a real product is not possible.

Increase in Shelf-life

0029 When the degradation reactions are known, it is pos-

sible to minimize their rate in order to increase the

shelf-life of the product. The basis of this approach is

the need to reduce the availability of the donor or

acceptor of the degradation agent.

0030 If the acceptor is water, its availability is reduced by

the addition of humectants (polyols, sugars, proteins)

to the formula of the baked goods. Such an addition

provokes a decrease in a

from about 0.85 to 0.75 for

a sponge cake, for example, which is then screened

from microbial spoilage.

0031 Preservation against oxidation and/or microbial

growth may be obtained by changing the inner

atmosphere of the package, generally by using a

mixture of nitrogen and carbon dioxide. A low

partial pressure of oxygen, together with a carbon

dioxide/nitrogen atmosphere, contributes to an in-

crease in the shelf-life; for example, industrial

pastry with a normal a

level of about 0.90 can

have its shelf-life extended to 3 months. (See

Chilled Storage: Use of Modified-atmosphere Pack-

aging; Packaging Under Vacuum; Chill Foods:

Effect of Modified-atmosphere Packaging on Food

Quality.)

0032 The stabilization of a solid food may also be

achieved by using a superficial thermal treatment

using radiant energy from infrared or microwave

radiation. Such a treatment applied to the packaged

product can contribute to an increase in the shelf-life.

0033 Protection of the product against degradation

is also obtained by the choice of a good barrier (poly-

meric film or laminate), which may be transparent or

opaque. The barrier properties of the packaging ma-

terial change if it interacts with degradation agents

like water vapor or oxygen. These interactions depend

on the hydrophilic or hydrophobic character of the

material. For products particularly sensitive to one or

other of the degradation agents, the packaging mater-

ial may include chemicals permitting the scavenging

of oxygen, the adsorption of water vapor, the emis-

sion of ethanol or carbon dioxide, and so on. The

packaging becomes an ‘active’ barrier of protection

and the center of a protective chemical reaction.

However, one should remember that adaptation of

the packaging material to food protection must be

economically feasable and that the objective is not

the absolute stability of the product during storage.

It is only needed for the solid food to be accepted by

the consumer.

Polymeric Packaging Materials used for

Solid Foods

0034The selection of polymeric or laminate film for

solid-food packaging involves a certain number of

conditions. The material must be compatible with

the food in accordance with the legislation and calcu-

lated (thickness) to fit with determined barrier

properties and shelf-life of the product. Depending

on the level of protection and kind of product to be

packed, the packaging material will be either a

monolayer or a multilayer (coextruded or laminated).

It may be coated or metallized, if the aim is to prevent

the transfer of water vapor or light, and the structure

of a foil reinforced by orientation or plasticizing.

0035A wide range of films used for baked goods are

listed in Table 1. The transfer of gases and water

vapor is expressed in commonly used units rather

than in SI units. The unit for the transmission rate of

gases is given in cubic centimeters of gas in 1 day for

1 square meter of film at a given thickness at constant

temperature and pressure. The rate of water vapor

transmission is expressed in grams per day per square

meter at a specific temperature and a given difference

of water vapor pressure (Dp) between the two sides of

the packaging material. When the barrier characteris-

tics required are not achievable with monolayer film,

laminates of multilayer material are used. The char-

acteristics of such laminates are listed in Table 2.As

may be seen in Tables 1 and 2, the basic films are

polyolefins, polyethylene, and polypropylene, co-

polymers like ethylene-vinyl alcohol and other

polymers such as polyesters, polyamides (OPA 6 and

66) and polyvinylchlorides. The laminated plastic

films are coated with regenerated cellulosics like

DM, which is nitrocellulose coated on one side,

MXXT, which is polyvinylidene chloride coated, or

paperboard or aluminum foils. Different laminating

adhesives are used.

0036Most foods are sensitive to water vapor, and the

packaging materials generally used are good barriers

to water vapor; polyesters (polyvinyldene chloride,

coated or metallized film) and oriented polypropylene

are the major materials found. Snacks and crisps

contain fats and have a large specific area. Therefore,

they require protection against light, which has a

catalytic effect on lipid oxidation. The laminates

used to protect these products utilize aluminum foils

(see Table 2). Metallized polyester is generally coated

with vaporized aluminum.

0037Food powders freely flowing are packaged in poly-

ethylene sealable films, which gives a good water

PACKAGING/Packaging of Solids 4313

vapor barrier and a transparent package allowing the

product to be seen. Refined sugar is generally packed

in multiwall paper packages, cardboard cartons, or

polyethylene coated paper. Finished packs contain

500 g to 5 kg for domestic use. Sacks of up to 50 kg

are produced for industrial utilization. An intermedi-

ate stage between the bulk transport of granulated

sugar and the 50-kg sacks is the big bag called

tbl0001 Table 1 Characteristics of some films used in the packaging of solid foods

Film (thickness 25 mm) Gas transmission (cm

3

2

day

1

(dry gas)) Water vapor transmission (gm

2

day

1

)

Oxygen 23



CCarbondioxide23



C Nitrogen 23



C DRH 90% 38



C DRH 75% 25



LDPE (0.917) 7 400.00 40 000.00 2 800.00 12.50 4.00

HDPE (0.960) 1 600.00 11 400.00 440.00 3.70 1.45

PP-cast 3 040.00 9 760.00 690.00 8.20 3.30

OPP-coextruded 1 550.00 5 280.00 320.00 5.00 1.35

OPP-coated 15.00 88.55 4.50 5.00 2.00

OPP acrylic-coated 1 200.00 4 500.00 250.00 4.60 1.80

OPP-metallized 35.00 108.00 6.50 1.00

PVC-rigid 120.00 320.00 20.00 32.00 12.00

PVC-oriented 27.00 68.00 20.00 17.50 7.00

PVC-plasticized 190–3 100 430–19 000 53–810 85.00 32.70

PVDC 1.25–14.5 5.0–50.0 0.4–2.5 0.6–3.20 0.25

PS-cast 4 500.00 11 000.00 640.00 170.00 70.00

SAN 900.00 2 800.00 120.00

Polycarbonate 3 200.00 17 500.00 450.00 178.00 72.50

PET 55.00 240.00 12.40 20.00 7.00

PET–PVDC-coated 8.00 32.00 2.00 8.50 3.40

PET-metallized 0.65 3.4–10 0.20 1.00 0.40

PA6 40.00 200.00 280.00 80–110

OPA6 18.00 120.00 9.00 130.00 28.30

PA 6.6 35.00 140.00 11.00 90.00 15.00–30.00

EVAL (32% ethylene) 0.16 0.45 80.00 32.00

Cellulosic fim 445MXXT A 8.75 80.00 3.65 8.60 3.40

LDPE, low-density polyethylene; HDPE, high-density polyethylene; PP, polypropylene; PVC, polyvinyl chloride; PVDC, polyvinylidene chloride; PS,

polystyrene; SAN, styrene acrylonitrile; PET, polyester; PA, polyamide; OPA, oriented polyamide; EVAL, ethyl-vinyl alcohol; MXXT, a PVDC coating.

tbl0002 Table 2 Characteristics of some laminates used in the packaging of solid foods

Laminate Gas transmission

(cm

3

2

day

1

(dry gas))

Water vapor transmission

(gm

2

day

1

)

Oxygen



Carbon

dioxide 23



Nitrogen



DRH 90%



DRH 75%



Cellulose film 280 XS þPE 40 mm 12.00 4.50 1.10

OPP coextruded 25 mm þOP coextruded 25 mm 650.00 2.60 0.95

PET coated PVDC 12 mm þPE 40 mm 5.00 15.00 1.00 3.70 1.40

M PET 12 mm þPE 80 mm 1.00 4.00 0.20 0.50 0.20

M PET 12 mm þM PET 12 mm þPE 80 mm <0.10 <0.10 0.00 0.15 0.06

OPA6 15 mm end. PVCD þPE 60 mm 10.00 30.00 2.50 5.00

OPA 6 20 mm þPE 80 mm 40–30

M OPA 6 15 mm þPE 80 mm 2.00 2.50

Kraft 45 g m

2

þPE 20 g m

2

þend. PVDC 20 g m

2

34.00 1.70 0.06

Kraft 60 g m

2

þend. PVDC 30 g m

2

15.00 1.90 0.65

PET 12 m m þ119 mm þmonomer 20 mm <0.20 <0.10

Cellulosic film 320 DM þA19mm þPE 35 mm 7.15 0.15 0.10

Kraft 70 g m

2

þPE 15 g m

2

þA19mm 4.30 0.10 0.08

A19mm þKraft 70 g m

2

25.40 0.25 0.15

A19mm þTPP 20 g m

2

wax 28.00 0.40 0.15

30 g m

2

TPP 20 g m

2

<8.00 <35.00 <3.00

M, metallized; Kraft, paper; DM, one-size nitrocellulose coated; A, aluminum foil; XS, cellulosic film coated with PVDC.

4314 PACKAGING/Packaging of Solids