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

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processes by preventing the activation of oxygen by

these pigments. The head space of products in con-

tainers can also be controlled to inhibit oxidative

processes. For example, foods can be sealed in con-

tainers after the head space has been flushed with an

inert gas such as nitrogen or under vacuum. Both

approaches serve to minimize the oxygen available

to support oxidative reactions. Products may also be

coated, such as with sugar syrups on fruits to be

frozen, to minimize the availability of oxygen for

oxidative reactions.

Examples in Foods

0032 Many foods are susceptible to oxidative reactions.

Plant and fish oils, due to their high levels of unsatur-

ation, can deteriorate in flavor very rapidly if oxida-

tion is allowed to take place. Lipid oxidation gives

rise to the ‘fishy’ flavor and aroma in frozen fish and

this limits acceptable storage life. Refining proced-

ures for vegetable and seed oils are partly designed

to remove chlorophyl which can cause flavor deterior-

ation by initiating photooxidative reactions. Another

light-sensitive food is milk. The endogenous riboflavin

can cause photooxidation of lipids and proteins and

yield the undesirable ‘light-activated flavor.’ Early rec-

ognition of this problem gave rise to the domestic

delivery of milk in opaque containers, in many coun-

tries, to prevent its exposure to light. (See Fish Oils:

Composition and Properties; Milk: Processing of

Liquid Milk; Vegetable Oils: Dietary Importance.)

0033 Nuts and high-fat products, such as potato crisps,

can be packaged in containers having a modified

atmosphere or head space. Nitrogen flushing of

containers and packing under vacuum are processes

designed to limit the amount of oxygen available for

oxidation reactions. (See Chilled Storage: Use of

Modified-atmosphere Packaging.)

0034 Most plant tissues, particularly fresh fruits, brown

excessively upon cutting or bruising. This is often due

to the presence of polyphenol oxidase, which acts on

phenolic acids in these foods. After the initial enzym-

atic oxidations, a series of subsequent nonenzymatic

oxidations convert these phenolic acids into polymers

that are responsible for the brown color. (See Phenolic

Compounds.)

0035Not all oxidative reactions in foods are undesir-

able. In the extrusion processing of foods at alkaline

pH, the oxidative polymerization of proteins results

in the desirable texturization in simulated meat prod-

ucts. Protein and lipid oxidation are also recognized

for their beneficial effects on dough strengthening in

the baking industries. A third example is the eman-

ation of characteristic flavors and aromas upon slicing

of fresh cucumbers and tomatoes. The sources of

these flavors are unsaturated fatty acids which have

been initially oxidized by endogenous lipoxygenase

activity and have been transformed further by other

enzymes. The chemical ‘fermentation’ of tea leaves

and the ‘ripening’ of olives are achieved by potentiat-

ing polyphenol oxidase enzyme activity on endogen-

ous phenolic acids, causing the development of

desirable coloration in these products.

0036Generally, oxidative reactions that can be con-

trolled can be manipulated to yield beneficial effects,

whereas those that cannot often yield detrimental

effects on food quality.

See also: Antioxidants: Natural Antioxidants; Synthetic

Antioxidants; Ascorbic Acid: Properties and

Determination; Browning: Nonenzymatic; Chilled

Storage: Use of Modified-atmosphere Packaging;

Chlorophyl; Fatty Acids: Metabolism; Fish Oils:

Composition and Properties; Milk: Processing of Liquid

Milk; Phenolic Compounds; Riboflavin: Properties and

Determination; Vegetable Oils: Dietary Importance;

Water Activity: Effect on Food Stability

Further Reading

Buettner GR (1993) The pecking order of free radicals and

antioxidants: lipid peroxidation, a-tocopherol, and

ascorbate. Archives of Biochemistry and Biophysics

300: 535–543.

Clark WM (1960) Oxidation–Reduction Potentials of

Organic Systems. Baltimore: Williams and Wilkins.

Frankel EN (1998) Lipid Oxidation. Dundee: Theory Press.

Kanner J, German JB and Kinsella JE (1987) Initiation of

lipid peroxidation in biological systems. CRC Critical

Reviews in Food Science and Nutrition 25: 317–364.

Packer L (ed.) (1984) Oxygen radicals in biological systems.

Methods in Enzymology 105.

Richardson T and Finley JW (eds) (1985) Chemical

Changes in Food During Processing. Westport, CT: AVI.

4294 OXIDATION OF FOOD COMPONENTS

OXIDATIVE PHOSPHORYLATION

D A Bender, University College London, London, UK

Background

0001 The total body content of ATP is of the order of 10 g,

whereas the daily turnover of ATP is equal to the

body weight, some 70 kg. A small number of meta-

bolic reactions involve direct transfer of phosphate

from a phosphorylated substrate on to ADP, forming

ATP – substrate-level phosphorylation. Under

normal conditions, almost all of the phosphorylation

of ADP to ATP occurs in the mitochondria, by the

process of oxidative phosphorylation – the oxidation

of reduced coenzymes linked to the reduction of

oxygen to water and (under normal conditions) ob-

ligatorily linked to phosphorylation of ADP !ATP.

This obligatory linkage of substrate oxidation, reox-

idation of reduced coenzymes, and reduction of

oxygen to water with the phosphorylation of ADP

mean that the availability of ADP controls the rate at

which substrates are oxidized. In turn, the availabil-

ity of ADP to be phosphorylated is dependent on the

rate of utilization of ATP in performing physical and

chemical work. Thus, energy expenditure in physical

and chemical work controls the rate at which

metabolic fuels are oxidized, rather than being used

to form reserves of (mainly) adipose tissue triacyl-

glycerol.

0002 With the exception of glycolysis and the pentose

phosphate pathway, most of the reactions in the oxi-

dation of metabolic fuels occur inside the mitochon-

dria and lead to the reduction of nicotinamide

nucleotide and flavin coenzymes. Within the inner

membrane of the mitochondrion, there is a series of

coenzymes that are able to undergo reduction and

oxidation. The first coenzyme in the chain is reduced

by reaction with NADH, and is then reoxidized by

reducing the next coenzyme. In turn, each coenzyme

in the chain is reduced by the preceding coenzyme,

and then reoxidized by reducing the next coen-

zyme. The final step is the oxidation of a reduced

coenzyme by oxygen, resulting in the formation of

water. Figure 1 shows an overview of this mitochon-

drial electron transport chain.

0003 Experimentally, the electron transport chain can be

dissected into four complexes of coenzymes, which

catalyze:

0004 Oxidation of NADH leading to the reduction of

ubiquinone to ubiquinol. This complex is associ-

ated with the phosphorylation of ADP !ATP.

0005Oxidation of reduced flavoproteins and reduction

of ubiquinone to ubiquinol. This complex is not

associated with phosphorylation of ADP.

0006Oxidation of ubiquinol, leading to reduction of

cytochrome c. This complex is associated with

the phosphorylation of ADP !ATP.

0007Oxidation of reduced cytochrome c leading to the

reduction of oxygen to water. This complex is

associated with the phosphorylation of ADP !

ATP.

This means that there are three sites in the electron

transport chain between NADH and oxygen that are

linked to the phosphorylation of ADP !ATP, but

only two between reduced flavoproteins and oxygen.

Experimentally, this is seen as a ratio of phosphate

esterified:oxygen consumed (the P:O ratio) of ap-

proximately 3 when substrates that reduce NAD

are oxidized, and approximately 2 when substrates

that reduce flavoproteins are oxidized.

0008Experimentally, mitochondrial metabolism is

measured using the oxygen electrode, in which the

percentage saturation of the buffer with oxygen is

measured electrochemically as the mitochondria oxi-

dize substrates and reduce oxygen to water. Figure 2

shows the oxygen electrode traces for oxidation of

malate (which is linked to reduction of NAD

)and

succinate (which is linked to reduction of a flavopro-

tein). The greater consumption of oxygen for oxida-

tion of succinate compared with the same amount

of malate reflects the lower P:O ratio for succinate

oxidation.

Substrate

oxidation

Substrate

oxidation

NADH, H

NAD

Flavin H

Flavin

Ubiquinone

Flavoprotein

ADP + Pi

ATP

ADP + Pi

ATP

ADP + Pi

ATP

Cytochrome b

Cytochrome c

Cytochrome oxidase

(cytochromes a and a

)

fig0001Figure 1 Overview of the mitochondrial electron transport

chain.

OXIDATIVE PHOSPHORYLATION 4295

0009 Figure 3 shows the oxygen electrode traces for

mitochondria incubated with varying amounts of

ADP, and a super-abundant amount of malate. As

more ADP is provided, so there is more oxidation of

substrate, and hence more consumption of oxygen.

This illustrates the tight coupling between the oxida-

tion of metabolic fuels and the availability of ADP to

be phosphorylated.

Mitochondrial Electron Transport Chain

0010 The mitochondrial electron transport chain is a series

of enzymes and coenzymes in the crista membrane,

each of which is reduced by the preceding coenzyme,

and in turn reduces the next, until finally the protons

and electrons that have entered the chain from either

NADH or reduced flavin reduce oxygen to water. The

sequence of the electron carriers shown in Figures

1 and 4 has been determined in two ways:

0011By consideration of their electrochemical redox

potentials, which permits determination of which

carrier is likely to reduce another, and which is

likely to be reduced.

0012By incubation of mitochondria with substrates, in

the absence of oxygen, when all of the carriers

become reduced, then introducing a limited

amount of oxygen, and following the sequence in

which the carriers become oxidized. The oxidation

state of the carriers is determined by following

changes in their absorption spectra.

Time

Mitochondria + Substrate added

ADP added

500 nmol ADP

1500 nmol ADP

% oxygen saturation

fig0003 Figure 3 Oxygen electrode traces for mitochondria oxidizing

malate with varying amounts of ADP.

NADH, H

NAD

Flavin

+++

Ubiqinone

Nonheme iron

protein

Nonheme iron

protein

Cytochrome b

Cytochrome c

Cytochrome aCytochrome a

Cytochrome a

Cytochrome cCytochrome c

Cytochrome c

Ubiquinol

Complex III

Complex I

Complex IV

Semiquinone

Semiquinone Flavin H

fig0004Figure 4 Mitochondrial electron transport chain.

Time

Mitochondria + 2500 nmol substrate added

1000 nmol ADP added

malate

succinate

% oxygen saturation

fig0002 Figure 2 Oxygen electrode traces for mitochondria oxidizing

malate and succinate.

4296 OXIDATIVE PHOSPHORYLATION

In order to understand how the transfer of electrons

through the electron transport chain can be linked to

the phosphorylation of ADP to ATP, it is necessary to

consider the chemistry of the various electron car-

riers. They can be classified into two groups:

0013 Hydrogen carriers, which undergo reduction and

oxidation reactions involving both protons and elec-

trons – these are NAD, flavins, and ubiquinone. As

shown in Figure 5, NAD undergoes a two-electron

oxidation/reduction reaction, while both the flavins

and ubiquinone undergo two single electron reactions

to form a half-reduced radical, then the fully reduced

coenzyme. Flavins can also undergo a two electron

reaction in a single step.

0014 Electron carriers, which contain iron (and, in the

case of cytochrome oxidase, also copper) undergo

oxidation and reduction by electron transfer alone.

These are the cytochromes, in which the iron is pre-

sent in a heme molecule, and nonheme iron proteins,

sometimes called iron–sulfur proteins, because the

iron is bound to the protein through the sulfur of

the amino acid cysteine. Figure 6 shows the arrange-

ment of the iron in nonheme iron proteins, and the

three different types of heme that occur in cyto-

chromes:

0015 heme (protoporphyrin IX), which is tightly but

noncovalently bound to proteins, including cyto-

chromes b and b

, as well as enzymes such as

catalase, and the oxygen transport proteins hemo-

globin and myoglobin;

0016 heme C, which is covalently bound to protein in

cytochromes c and c

;

0017 heme A, which is anchored in the membrane by its

hydrophobic side chain, in cytochromes a and a

(which together form cytochrome oxidase).

The hydrogen and electron carriers of the electron

transport chain are arranged in sequence in the crista

membrane, as shown in Figure 4. Some carriers are

entirely within the membrane, whereas others are

located on the inner or outer face of the membrane.

Each of the three complexes in which phosphoryl-

ation of ADP !ADP is linked to electron transport

forms a membrane-spanning unit.

0018 There are two steps in which a hydrogen carrier

reduces an electron carrier: the reaction between the

flavin and nonheme iron protein in complex I, and the

reaction between ubiquinol and cytochrome b plus a

nonheme iron protein in complex III. The reaction

between nonheme iron protein and ubiquinone in

complex I is the reverse – a hydrogen carrier is re-

duced by an electron carrier.

0019 When a hydrogen carrier reduces an electron car-

rier, there is a proton that is not transferred onto the

electron carrier, but is extruded from the membrane,

into the crista space, as shown in Figure 7. When an

electron carrier reduces a hydrogen carrier, there is a

need for a proton to accompany the electron that is

transferred. This is acquired from the mitochondrial

matrix, thus shifting the equilibrium between H

and H

þOH



, resulting in an accumulation of

hydroxyl ions in the matrix.

0020Similar pumping of protons across the crista mem-

brane occurs in complexes III and IV, although it is

less obvious than in complex I. Thus, each complex

that is associated with phosphorylation of ADP !

ATP pumps protons into the crista space as it trans-

ports electrons.

Phosphorylation of ADP Linked to

Electron Transport

0021The result of electron transport through the sequence

of carriers shown in Figure 4 is a separation of protons

and hydroxyl ions across the crista membrane, with

an accumulation of protons in the crista space, and an

accumulation of hydroxyl ions in the matrix, i.e.,

creation of a pH gradient across the crista membrane.

0022This proton gradient provides the ‘driving force’

for the phosphorylation of ADP !ATP – a highly

endothermic reaction. Protons reenter the mitochon-

drial matrix, down the proton gradient, through

transport pores in the membrane that are an integral

part of the mitochondrial primary particles that con-

tain the ATP synthase, and form the transmembrane

stalk of the primary particles.

0023ATP synthase acts as a molecular motor, driven by

the flow of protons down the concentration gradient

from the crista space into the matrix, through the

transmembrane stalk of the primary particle. As

protons flow through the stalk, they cause rotation

of the core of the multienzyme complex that makes

up the primary particle containing ATP synthase.

0024As shown in Figure 8, there are three ATP synthase

catalytic sites in the primary particle, and each one-

third turn of the central core causes a conformational

change at each active site:

0025at one site, the conformational change permits

binding of ADP and phosphate;

0026at the next site, the conformational change brings

ADP and phosphate close enough together to

undergo condensation and expel water;

0027at the third site, the conformational change causes

expulsion of ATP from the site, leaving it free to

accept ADP and phosphate at the next part turn.

At any time, one site is binding ADP and phosphate,

one is undergoing condensation, and one is expelling

OXIDATIVE PHOSPHORYLATION 4297

CONH

Oxidized coenzyme

NAD

or NADP

Reduced coenzyme

NADH

or NADPH

+ H

CH CH CH

OH OH OH

CH CH CH

OH OH OH

CH CH CH

OH OH OH

, e

−

, e

−

, e

−

, e

−

, e

−

Fully reduced riboflavin

Riboflavin semiquinone radical

Oxidized ubiquinone

Oxidized riboflavin

Fully reduced ubiquinol

Half-reduced semi-quinone radical

Figure 5 Oxidation and reduction of the hydrogen carriers of the electron transport chain: the nicotinamide nucleotide coenzymes (NAD and NADP), flavins and ubiquinone.

fig0005

ATP. If ADP is not available to bind, rotation cannot

occur – and if rotation cannot occur, protons cannot

flow through the stalk from the crista space into the

matrix.

Coupling of Electron Transport, Oxidative

Phosphorylation, and Fuel Oxidation

0028 The processes of oxidation of reduced coenzymes and

the phosphorylation of ADP ! ATP are normally

tightly coupled:

0029ADP phosphorylation cannot occur unless there is

a proton gradient across the crista membrane

resulting from the oxidation of NADH or reduced

flavins.

0030If there is little or no ADP available, the oxidation

of NADH and reduced flavins is inhibited, because

the protons cannot cross the stalk of the primary

Crista membrane Mitochondrial matrixCrista space

, e

−

, e

−

NADH, H

NAD

−

Hydrogen carrier

Electron carrier

fig0007 Figure 7 Proton pumping across the crista membrane in

complex I.

Heme

(protoporphyrin IX)

Nonheme iron protein (iron−sulfur protein)

Heme A

Heme C

HC SCH

COOH

CH CH

SCH

OC CH

OC NH

OC CH

OC NH

fig0006 Figure 6 Types of heme in cytochromes and the binding of iron in nonheme iron proteins (iron–sulfur proteins).

Site A

Site B

Site C

ATPH

ATP

ADP + P

fig0008Figure 8 Three active sites of the ATP synthase complex in the

mitochondrial primary particle.

OXIDATIVE PHOSPHORYLATION 4299

particle, and so the proton gradient becomes large

enough to inhibit further transport of protons into

the crista space. Indeed, experimentally, it is pos-

sible to force reverse electron transport, and reduc-

tion of NAD

and flavins by creating a proton

gradient across the crista membrane.

Metabolic fuels can only be oxidized when NAD

and oxidized flavoproteins are available. Therefore,

if there is little or no ADP available in the mitochon-

dria (i.e., it has all been phosphorylated to ATP),

there will be an accumulation of reduced coenzymes

and hence a slowing of the rate of oxidation of

metabolic fuels. This means that substrates are only

oxidized when there is a need for the phosphoryl-

ation of ADP to ATP, and ADP is available. In turn,

the availability of ADP is dependent on the utiliza-

tion of ATP in performing physical and chemical

work.

0031 It is possible to uncouple electron transport and

ADP phosphorylation, by adding a weak acid such

as dinitrophenol that transports protons across the

crista membrane. As shown in Figure 9, in the

presence of such an uncoupler, the protons ex-

truded during electron transport do not accumulate

in the crista space, but are transported into the

mitochondrial matrix, where they react with hy-

droxyl ions, forming water. Under these conditions,

ADP is not phosphorylated to ATP, and the oxida-

tion of NADH and reduced flavins can continue

unimpeded until all the available substrate or

oxygen has been consumed. Figure 10 shows the

oxygen electrode trace in the presence of an uncou-

pler – there is more or less complete consumption

of oxygen regardless of the amount of ADP

present.

0032 The result of uncoupling electron transport from

the phosphorylation of ADP is that a great deal of

substrate is oxidized, with little production of ATP,

although heat is produced. This is one of the physio-

logical mechanisms for heat production to maintain

body temperature without performing physical work

– nonshivering thermogenesis. There are a number of

proteins in the mitochondria of various tissues that

act as proton transporters across the crista membrane

when they are activated.

0033 The first such uncoupling protein to be identified

was in brown adipose tissue, and was called thermo-

genin because of its role in thermogenesis. Brown

adipose tissue is anatomically and functionally dis-

tinct from the white adipose tissue that is the main

site of fat storage in the body. It has a red–brown color

because it is especially rich in mitochondria. Brown

adipose tissue is especially important in the mainten-

ance of body temperature in infants, but it remains

active in adults, although its importance compared

with uncoupling proteins in muscle and other tissues

is unclear.

0034In addition to maintenance of body temperature,

uncoupling proteins are important in overall energy

balance and body weight control. The hormone lep-

tin, secreted by (white) adipose tissue, increases the

expression of uncoupling proteins in muscle and adi-

pose tissue, so increasing energy expenditure and the

utilization of adipose tissue fat reserves.

Control

+ Uncoupler

Time

Mitochondria + Substrate added

% oxygen saturation

1000 nmol ADP uncoupler added

fig0010Figure 10 Oxygen electrode traces in the presence and

absence of an uncoupler.

−

Electron transport chain

Crista membrane Mitochondrial matrixCrista space

fig0009Figure 9 Uncoupling – discharge of the proton gradient by a

weak acid.

4300 OXIDATIVE PHOSPHORYLATION

Respiratory Poisons and other Inhibitors

0035 Much of our knowledge of the processes involved in

electron transport and oxidative phosphorylation has

come from studies using inhibitors.

0036 Rotenone, the active ingredient of derris powder,

an insecticide prepared from the roots of the leg-

uminous plant Lonchocarpus nicou. It is an inhibi-

tor of complex I. The same effect is seen in the

presence of amytal (amobarbital), a barbiturate

sedative drug, which again inhibits complex I.

These two compounds inhibit oxidation of malate,

which requires complex I, but not succinate,

which reduces ubiquinone directly. The addition

of an uncoupler has no effect on malate oxidation

in the presence of these two inhibitors of electron

transport, but results in uncontrolled oxidation of

succinate.

0037 Antimycin A, an antibiotic produced by Strepto-

myces spp. that is used as a fungicide against fungi

that are parasitic on rice. It inhibits complex III,

and thus inhibits the oxidation of both malate and

succinate, since both require complex III, and the

addition of the uncoupler has no effect.

0038 Cyanide, azide, and carbon monoxide bind irre-

versibly to the iron of cytochrome a

, and thus

inhibit complex IV. Again, these compounds in-

hibit oxidation of both malate and succinate, since

both rely on cytochrome oxidase, and again, the

addition of the uncoupler has no effect.

0039 Oligomycin, a therapeutically useless antibiotic

produced by Streptomyces spp. Oligomycin in-

hibits the transport of protons across the stalk of

the primary particle. This results in inhibition of

oxidation of both malate and succinate, since, if

the protons cannot be transported back into the

matrix, they will accumulate and inhibit further

electron transport. In this case, addition of the

uncoupler permits reentry of protons across the

crista membrane, and hence uncontrolled oxida-

tion of substrates.

0040Atractyloside (a plant glycoside) and bongkrekic

acid (a toxic antibiotic formed by Pseudomonas

cocovenans growing on coconut – this is named

after bongkrek, a mold-fermented coconut prod-

uct in Indonesia, that becomes highly toxic when

Ps. cocovenans outgrows the mold). Both com-

pounds inhibit the transport of ADP and ATP

across the mitochondrial membrane. Bongkrekic

acid fixes nucleotides to the transport protein at

the matrix side of the membrane, so that they

cannot be released, whereas atractyloside has a

higher affinity for the transport protein than does

ADP, and so out-competes it for transport into the

matrix.

See also: Adaptation – Nutritional Aspects; Adipose

Tissue: Structure and Function of White Adipose Tissue

Further Reading

Bender DA (2002) Introduction to Nutrition and Metabol-

ism, 3rd edn. London: Taylor & Francis.

Boyer PD (1997) The ATP synthase – a splendid molecular

motor. Annual Reviews of Biochemistry 66: 717–749.

Murray RK, Granner DK, Mayes PA and Rodwell VW

(2000) Harper’s Biochemistry, 25th edn. New York:

McGraw-Hill.

Oysters See Shellfish: Characteristics of Crustacea; Commercially Important Crustacea; Characteristics of

Molluscs; Commercially Important Molluscs; Contamination and Spoilage of Molluscs and Crustaceans;

Aquaculture of Commercially Important Molluscs and Crustaceans

OXIDATIVE PHOSPHORYLATION 4301

PACKAGING

Contents

Packaging of Liquids

Packaging of Solids

Aseptic Filling

Packaging of Liquids

S D Deshpande, Central Institute of Agricultural

Engineering, Nabi Bagh, Bhopal, India

Background

0001 In modern times, packaging has been identified as an

integral part of processing in the food industry. Pack-

aging is a technique of using the most appropriate

packaging media for the safe delivery of the contents

from the centers of production to the site of consump-

tion. Packaging serves as the vital link in the long line

of production, storage, transportation, distribution,

and marketing. The package must ensure the same

high quality of the product to the consumer, as they

are used to getting, in freshly manufactured products.

It is important that all products should reach the

consumer in a usable condition.

0002 Modern packaging systems for liquid foods are

products from a synthesis of demands from pro-

ducers, distributors, and consumers. The need for

hygiene is the primary reason for retail packaging of

perishable liquid food products like milk. Although

this was realized more than a century ago, packaging

techniques for liquid milk were slow in developing.

The advent of pasteurization in the 1920s made retail

packaging of liquid essential, and the returnable glass

bottle was soon to become universal.

0003 The commercial development of plastic materials,

starting with polyethylene (PE) in the 1940s, opened

up new possibilities for improving hygiene in liquid

packaging. PE ultimately became the most frequently

used thermoplastic in paper and carton board coating

processes, also finding uses in inplant manufacture

of packages from reel stock by form–fill–seal

techniques. In current efforts to make retailing still

more efficient, the focus is on standardized packages

and transport wrappings, the aim being to simplify

routines and cut costs. One-way cartons are suitable

for these requirements. These developments have

gradually led to a change in retail patterns in many

countries, and the replacement of returnable glass

bottles by single-service paper/plastic containers has

been seen in many countries.

0004Today, a product distinction can be made between

milk and non-milk on the one hand, and fresh and

long-life products on the other. The main products

retailed in one-way cartons are still milk and milk

products, holding approximately 80% of the carton

demand in liquid packaging, but a steady increase

in market share for fruit juices, mineral water, sports

drinks, vegetable oils and juices, soft drinks, and wine

is observed. This trend is likely to continue, ensuring

a further potential for the paper bottle.

Functional Packaging

0005Functional packaging of products contributes to the

industrial prosperity of a country through optimal

utilization of resources. The packaging has to protect

the contents against hazards such as the vagaries of

climate and transportation. During the course of the

journey, the package would be exposed to varying

climatic conditions, often resulting in evaporation

and condensation of water of the contents inside

the package. Also, atmospheric gases like O

and

contribute to the deterioration of the products

by the oxidation of fat-rich products or corrosion

of the metal containers. While this is the case in

bulk packages, the unit container, which comes dir-

ectly into contact with the product, must have requis-

ite barriers and protective properties. A scientifically

designed package should, therefore, afford protection

against egress or ingress of moisture, flavor loss or

odor pickup, light, oxygen, microbial and fungus

attack, as well as being compatible with the food

packaged. The package must preserve the quality,

freshness, and functional performance of the prod-

uct, afford the requisite shelf-life, and make it pos-

sible for the product to reach the consumer in prime

condition.

Principles of Production

0006 Filling and sealing machines for paper-based pack-

ages for liquids form two groups: those that work

from a roll of packaging material, and those that

work from premanufactured blanks, the difference

reflecting the basic machine philosophy or concepts

of companies like Tetra Pak and Elopak. The basic

idea of Tetra Pak is that the package should be formed

from a roll of packaging material, filled, and sealed in

a continuous, closed process. The basic idea of Elo-

pak is that as much of the package production as

possible should be included in the converting process.

Consequently, the production of blanks, being a

highly specialized process, is therefore considered

best performed when separated from the food-

packaging plant.

Converting

0007 In the converting process, the basic paper is coated on

both sides, printed, and provided with scorelines to

facilitate creasing when finally forming the package.

Filling and Sealing

0008 When choosing a carton-based packaging system for

liquids, there are three differently shaped packages

presently predominating the market, namely the

gable top, the tetrahedron, and the brick.

0009The filling and sealing procedure of a gable-top-

type package starts with a blank being fed from

a magazine. The lay-flat tube is then unfolded and

enters a mandrel where the bottom is heated with hot

air. The bottom is then folded in accordance with

scorelines, and pressure is applied for finishing the

bottom sealing. Now an open rectangular box, it is

removed from the mandrel on to a conveyer, filled

with liquid and the top sealed. The top seal is made

using hot air and pressure.

0010The most striking feature of the tetrahedral pack-

age is the shape. The tetrahedral shape requires less

packaging material than other designs, as it offers the

most favorable ratio of area to volume.

0011The production of Tetra Brik-type packages from

roll-fed machines follows basically the same prin-

ciples as those for Tetra Standard, but the transverse

seams are sealed parallel. The characteristic brick

shape is formed after cutting off individual packages

from the tube, by folding in the flaps and heat-sealing

them.

Materials

0012The sandwich construction of the two common paper-

based laminates used in liquid packaging is shown in

Figure 1. If no high-gas barrier is required, the mater-

ial consists of paper with a polyethylene coating on

both sides. The paper layer may consist of unbleached,

bleached, or semibleached sulfate pulp or laminates of

these. The paper layer, being responsible for much of

the machinability and mechanical properties of the

package, requires a high and stable quality.

0013Additional barrier properties are usually provided

by aluminum foil, laminated to the board, but the

contact surface against the food remains polyethylene.

(a) (b)

fig0001 Figure 1 Sandwich construction of two common laminates for carton containers. (a) Typical laminate for short-life products like

fresh milk consisting of (1) exterior PE, (2) paper, and (3) interior PE; (b) typical laminate for long-life products consisting of (1) exterior

PE, (2) paper, (3) Surlyn, (4) Al-foil, (5) Surlyn, and (6) interior PE.

4304 PACKAGING/Packaging of Liquids