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

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[48] b-Selinene

[49] b-Caryophyllene

Other

[50] Eugenol

[51] Carvacrol

[52] Thymol

[53] Estragole

[54] Anethole

[55] Safrole

[56] Myristicin

CHO

[57] Cinnamaldehyde

[58] 1,3,8,p-Menthatriene [59] 1-Methyl-4-isopropenylbenzene

[60] (þ)-ar-Curcumene

Continued

Table 3 Continued

SPICES AND FLAVORING (FLAVOURING) CROPS/Properties and Analysis 5497

Extraction Techniques

0018 Extraction with organic solvents This technique is

frequently used, like steam distillation. It involves put-

ting aromatic plants in a static extraction vessel and

covering them with an organic solvent, such as hexane,

benzene, toluene, ethanol, or light petroleum or a

binary mixture. Once equilibrium has been reached

(or at least nearly so), the solution is separated, and

the solvent is evaporated in a vacuum to yield the

extract. Two particular methods are extraction with

water and extraction with aqueous alcohol.

0019 The choice of the solvent depends on many tech-

nical and economic parameters, in particular: select-

ivity; boiling point; diffusivity; miscibility with water;

facility for recycling; safety – in general, the solvent

chosen must be of as low a toxicity as possible both

for operation of the extraction process and for con-

sumption of the product.

0020The process of extraction used also depends on the

nature of vegetable matter, such as its thermal lability,

the operating temperature ranging from ambient to

the boiling point.

0021According to the technique and solvent used, the

products are known by one of the following names:

0022Tinctures: obtained either by treating natural raw

materials with ethanol or ethanol–water mixtures

or by dissolving an extract in these solvents.

0023Oleoresins: concentrated extracts with a character-

istic odor and/or flavor, obtained from a natural

raw material.

0024Resinoids: concentrated nonaqueous extracts with

a characteristic odor obtained from a dried natural

raw material.

0025Concretes: concentrated nonaqueous extracts with

a characteristic odor and/or flavor obtained from a

fresh natural raw material.

0026Besides odorant compounds, the organic solvent

also extracts such undesirable substances as waxes

and lipids, which are responsible for the nature of

‘concretes.’ In fact, a transformation is needed from

concrete to absolute. Because waxes are not soluble in

alcohol at low temperatures (about 10



C), the con-

crete is diluted with alcohol at 30–40



C and strongly

stirred. When this alcohol solution is refrigerated at

5to10



C, waxes precipitate and are filtered off.

The filtrate is concentrated under vacuum, and after

elimination of alcohol, the absolute remains. Gener-

ally absolutes are in liquid form, though they may be

viscous or ‘pasty.’

0027CO

extraction This process (see Figure 2) uses high

pressure and, depending on the characteristics desired

in the product, employs either liquid carbon dioxide

(300 bar, 30



C) or supercritical carbon dioxide (350

[61] p-Cymene

(1)

(3)

[62] Turmerone

[63] ar-Turmerone

Compounds [4a] and [4b], which occur as cis and trans isomers in wines, are also known as linalooloxides.

Corresponding aldehydes genanial, neral, and citronellal also occur in foods. Citral is a mixture of neral and geranial.

The corresponding acid is an important aroma constituent of wine cultivars ‘Traminer’ and ‘Scheurebe.’

()-3,7-Dimethyl-1,5,7-octatrien-3-ol (hotrienol) is found in grape, wine, and tea aromas.

From Belitz H-D and Grosch W (1987) Food Chemistry. Berlin: Springer.

Probe

Column

Input

Raw

material

Heating

jacket

Distillate

Probe

Vacuum pump

Pressure

Water

Condensers

θ'

Circulation

fig0001 Figure 1 Vacuum distillation column. Reproduced from Spices

and Flavouring Crops: Properties and Analysis, Encyclopaedia of

Food Science, Food Technology and Nutrition, Macrae R, Robinson

RK and Sadler MJ (eds), 1993, Academic Press.

Table 3 Continued

5498 SPICES AND FLAVORING (FLAVOURING) CROPS/Properties and Analysis

bar, 50



C). The separation of extract takes place in

the gas phase by a simple separation of gas and liquid.

0028 The principle of the method is based on good solu-

bility in carbon dioxide of most odorants of vegetable

matter and semifinished products, such as concrete

or even essences. The technique has the following

advantages:

0029 No residual toxic solvent, particularly important

for materials used in flavors.

0030 Low process temperature, important when pro-

cessing unstable and heat-sensitive products.

0031 Selectivity (e.g., in caffeine extraction).

0032 Lack of fire hazards.

0033 Energy efficiency (no loss of organic solvents such

as hexane or benzene, which have to be redistilled

for use again).

Carbon dioxide as a solvent is relatively nonpolar, so

its solubilizing powers are comparable to, but slightly

more polar than, those of hexane. The latter is used

frequently in the production of aromatic vegetable

matter.

0034 Extraction using ultrasound This process consists of

vibrating the material by means of supersonic waves,

which, owing to resonance, disintegrates the product

matrix. More particularly, when the process is carried

out in a liquid medium, the vibrational energy applied

produces pressure variations that greatly facilitate

the dispersion of the desired products in the solvent

after they have been separated from their natural

matrices.

Expression

0035Expression of oil at low temperature is a response to

two particular features of the essential oils of citrus

plants: (1) these oils contain terpene peroxides and

polymerizable terpenes, so that they are heat-sensitive

to hydrodistillation temperatures; (2) the oils are

located in the porous pericarp, which is easily torn.

It is therefore preferable to recover the essential oils

by simple mechanical action.

0036It is the only process for treatment of aromatic

plants without using a fluid extraction phase and

involves either expressing the pericarp by water pres-

sure or crushing whole fruits in a metallic cylinder.

The essences so produced have low densities and can

be separated from the aqueous phase by centrifuga-

tion. They are also designated ‘essential oil.’

Specialized Extraction Techniques

0037Molecular distillation Molecular or short-path dis-

tillation is used to obtain colorless products; more

stable products, because of the elimination of con-

stituents with higher molecular weight (acids, pig-

ments); and more delicate notes, because of the

increase in the proportion of odorant in the oil.

0038Because of the high vacuum (0.05–0.0005 torr),

the boiling point and extraction time are greatly

Pressure

θ'

Heat exchanger

(HE)

Compressor

Separator

(extract)

Charcoal trap

θ'< θ

P'< P

P > 1071 psi

θ >318C

Extractor

raw material

or semifinished

product + CO

Safety valve

fig0002 Figure 2 CO

extraction system. Reproduced from Spices and Flavouring Crops: Properties and Analysis, Encyclopaedia of Food

Science, Food Technology and Nutrition, Macrae R, Robinson RK and Sadler MJ (eds), 1993, Academic Press.

SPICES AND FLAVORING (FLAVOURING) CROPS/Properties and Analysis 5499

reduced, thus preventing the loss of some heat-

sensitive notes in the oil. The product to be proces-

sed is combined with a heavy, and a light solvent and is

then passed through the first short-path evaporator;

the most volatile components condense together

with the light solvent on a so-called ‘finger’ in the

middle of the evaporator and are recovered as the

first distillate (see Figure 3). The other components

condense on the walls of the evaporator and are

pumped into a second short-path evaporator. Here

again, the next most volatile components of the oil

condense on the inner ‘finger’ and are recovered

as the second distillate. The residues and the heavy

solvent condense on the walls and are recovered in the

residue tank.

0039 Simultaneous distillation/extraction This original

process was designated by Likens and Nickerson. It

uses two fluids; the volatile compounds are removed

by steam distillation, and a nonpolar solvent continu-

ously extracts them from the aqueous distillate.

0040The geometry of the apparatus enables the steam

carrying the volatiles and the solvent vapor to meet

in the condenser. The condensate separates into two

phases, which are directed to their respective vapor

generators. Eventually, the evaporation of the solv-

ent allows recovery of a concentrated solution of

odorant.

0041The relative position of two vapor generators

differs according to the density of the solvent used.

The method is particularly applicable in the study of

rare vegetable materials.

0042Capture of headspace Three methods have been

used as follows:

0043Adsorption in liquid, which allows capture of the

volatile components by passing the head space

vapors through a solvent, and then concentrating

the solution by evaporation.

0044The cryogenic method, which condenses the vola-

tile components in a series of refrigerated traps.

Low temperature trap

Nitrogen cooling system

Oil diffusion pump

Condensate vessel flask

2nd Distillate flask

Residue flask

1st Distillate flask

Graduated vessel

Water cooling system

Vacuum pump filters

Vacuum pump

Product

to be

processed

Pressure retention valve

Manometer

Agitator

Heat exchanger

Short-path evaporator

fig0003 Figure 3 Molecular distillation unit. Reproduced from Spices and Flavouring Crops: Properties and Analysis, Encyclopaedia of Food

Science, Food Technology and Nutrition, Macrae R, Robinson RK and Sadler MJ (eds), 1993, Academic Press.

5500 SPICES AND FLAVORING (FLAVOURING) CROPS/Properties and Analysis

This method has been used particularly for the

capture of the volatile components of fruit.

0045 Adsorption of solids, which involves passing the

headspace over an adsorbent, such as XAD-4

(polystyrene) or TENAX [poly(2,6-diphenyl-p-

phenylene oxide)]. The volatiles are recovered by

thermal desorption or by elution with an organic

solvent.

Volatiles

0046 Odorants must be volatile to some extent, and this

property is common in those molecules that contain

fewer than 10 carbon atoms, for example, monoter-

penes and their derivatives. It must be noted that alde-

hydes, ethers, and esters generally have a stronger odor

than their parent hydrocarbons. This is why they are

used for head notes in the formation of perfumes,

cosmetics, and deodorants.

0047 Volatiles of higher molecular mass evaporate rela-

tively slowly at room temperature; because of this

property, such compounds provide the more persist-

ent odors.

Nonvolatiles

0048 Nonvolatiles such as sugar, salt, piperine, and caf-

feine, may affect taste, although they cannot be

detected by smell at room temperature.

Mechanism of Degradation and Staling

0049 During steam distillation of an essential oil, terpenoid

compounds are susceptible to degradation. Terpene

alcohols and esters, especially, undergo a variety of

well-known chemical reactions (hydrolysis, hydra-

tion, and cyclization), in particular under acidic

conditions. For example, low pH values induce con-

siderable hydrolysis of linalyl acetate and extensive

rearrangement reactions. It is well known that ter-

tiary alcohols and their esters are protonated in aque-

ous media to yield oxonium ions, which split to form

a tertiary carbocation; thus, degradation reactions

and rearrangements can be observed under the condi-

tions of steam distillation.

0050 In the mechanism of linalyl acetate thermal degrad-

ation, the generation of a primary allylic carbocation

– the linalyl carbocation, which creates a p-menthane

skeleton by cyclization – explains the presence of

nerol and geraniol among the degradation products.

0051 Some degradation can take place during the storage

of essential oils, especially for oxygenated compon-

ents. For example, citronellal can be resinified in a

basic medium or oxidized in contact with air in the

presence of light.

0052Since flavoring compounds are volatile, they can be

lost easily by evaporation, thus leading to staling if

the conditions of storage are not appropriate.

Microbiological Contamination

0053A number of essential oils, as well as some spices and

aroma extracts, e.g., thyme and cloves, which are rich

in phenolic compounds, possess antifungal and anti-

bacterial properties. In general, essential oils have a

good bacteriological quality, provided humidity is

not too high. In contrast, the chemical stability of

some essential oils is limited on account of oxidation,

for example, those that are rich in limonene. Such

essential oils must be protected against oxidation

during storage. (See Spoilage: Chemical and Enzym-

atic Spoilage; Bacterial Spoilage.)

0054Bacteriological contamination is a hazard for

spices and aroma extracts, particularly if they are

aqueous extracts, for example, alliaceous extracts. It

is necessary to ensure their bacteriological quality.

The chemical stability for certain extracts, such as

pepper and rosemary, is protected by the presence

of natural antioxidants. (See Antioxidants: Natural

Antioxidants.)

See also: Antioxidants: Natural Antioxidants; Browning:

Nonenzymatic; Essential Oils: Properties and Uses;

Isolation and Production; Flavor (Flavour) Compounds:

Structures and Characteristics; Phenolic Compounds;

Sensory Evaluation: Aroma; Taste; Spoilage: Chemical

and Enzymatic Spoilage; Bacterial Spoilage

Further Reading

Association Franc¸aise de Normalisation (1988) Contro

de la qualite

des produits alimentaires – Epices et

Aromates, 2nd edn. Paris: AFN.

Bicchi C and Sandra P (1987) Capillary Gas Chromatog-

raphy in Essential Oils Analysis. Heidelberg: Springer.

Cu Jian Qin (1990) Extraction de Compositions Odorantes

tales. PhD thesis, Institut Polytechnique de Tou-

louse No. 393.

International Standards Organization (1984) Essential Oils

– Terminology. Murcia: ISO.

Meyer-Warnod B (1984) Natural essential oils – extraction

processes and application to some major oils. Perfumer

& Flavorist 9(2): 93–104.

Morin Ph and Richard H (1984) Thermal degradation

of linalyl acetate during steam distillation. In: Pro-

ceedings of The 4th Weurman Flavor Research Sympo-

sium, Dourdan, France, pp. 563–576. Amsterdam:

Elsevier.

SPICES AND FLAVORING (FLAVOURING) CROPS/Properties and Analysis 5501

SPOILAGE

Contents

Chemical and Enzymatic Spoilage

Bacterial Spoilage

Fungi in Food – An Overview

Molds in Spoilage

Yeasts in Spoilage

Chemical and Enzymatic

Spoilage

N F Haard, University of California, Davis, CA, USA

Introduction

0001 The storage life of foodstuff is limited by the occur-

rence of chemical reactions which alter edible quality,

including deterioration in optimal color, appearance,

texture, aroma, flavor, nutrition, safety, and functional

properties. When food undergoes deterioration in

quality, it is not always clear whether the reaction

causing the problem is of nonenzymatic, enzymatic,

or microbial origin. For example, development of bad

odor in stored coleslaw prepared with mayonnaise and

sour cream was first attributed to microbial spoilage.

However, investigation of the problem revealed that

endogenous enzymes in the cabbage were activated

by the anaerobic conditions in the package and were

responsible for the formation of offensive- smelling

volatiles. Likewise, enzymatic reactions rather than

microbial spoilage was shown to be the primary cause

of early spoilage in chilled, properly handled fish, by

studying the initial quality loss of the flesh in sterile and

nonsterile fish. In most cases, chemical and microbial

spoilage acts in concert. For example, in cold-smoked

salmon microbial activity causes production of charac-

teristic spoilage off-odors and off-flavors while auto-

lytic enzymes from the fish tissue areresponsible for the

characteristic texture deterioration. Moreover, there

are also many instances where chemical, enzymatic,

and microbial spoilage reactions are interactive

processes. For example, products of nonenzymatic

browning have been shown to inhibit other enzymatic,

nonenzymatic, or microbial spoilage reactions.

Chemical Reactions that Contribute to

Spoilage

0002 Chemical spoilage includes enzyme-catalyzed reac-

tions as well as nonenzymatic reactions. In general,

enzyme-catalyzed reactions are of primary concern in

untreated plant and animal tissues and nonenzymatic

reactions predominate in properly processed food-

stuffs. There are, however, some exceptions to this

general rule. In addition, enzymatic and nonenzy-

matic spoilage reactions may act in concert. For

example, discoloration of the surface of red meats is

caused by a nonenzymatic reaction, oxidation of myo-

globin (Fe

2þ

) to form metmyoglobin (Fe

3þ

). However,

enzymatic reactions involved with respiration at the

tissue surface can lower oxygen concentration and

indirectly promote nonenzymatic oxidation of myo-

globin. Some muscle tissues also contain the enzyme

metmyoglobin reductase, which catalyzes the reduc-

tion of metmyoglobin back to myoglobin. Likewise,

the nonenzymatic denaturation and aggregation of

myosin primarily cause texture deterioration during

frozen storage of certain species of fish. However,

these reactions may be accelerated by the action of

trimethylamine oxide demethylase, which forms for-

maldehyde, or by phospholipase, which forms free

fatty acids. It is normally possible to distinguish be-

tween enzymatic and nonenzymatic catalyzed spoil-

age reactions by conducting simple experiments

(Table 1).

Physiological Processes

0003Some spoilage reactions are of biological origin, i.e.,

are ‘of or pertaining to living organisms,’ and these

include sets of enzyme-catalyzed reactions. For

example, a set of biological reactions described

under the general heading ‘postharvest physiology

of fruits and vegetables’ are important because they

may contribute to deteriorative processes such as

plant senescence, wound response, chilling injury,

and other types of stress response. Physiological

processes in fruits and vegetables also lead to

desirable changes such as fruit ripening, wound

healing after harvest, and the reduction of reducing

sugars during the ‘conditioning’ of potato tubers.

Likewise, ‘postmortem physiology of food myosys-

tems’ describes a set of reactions that normally

cause a desired conversion of muscle to meat.

5502 SPOILAGE/Chemical and Enzymatic Spoilage

However, in some cases postmortem reactions may

contribute to poor-quality meat, e.g., ‘burnt tuna,’

‘pale, soft, exudative pork,’‘cold shortening,’ and

‘thaw rigor.’

0004 Spoilage reactions in the case of harvested and

stored plant and animal tissues are, for the most

part, catalyzed by enzymes. Myriad enzymes occur

naturally in biological tissues used by humans for

food. There is remarkable similarity in the basic

metabolism of biological cells. However, the

amounts and different kinds of specific enzymes pre-

sent in a given cell may be quite distinctive because

of heritable characteristics, intrinsic factors such as

age of the source organism, and extrinsic factors

such as preharvest stress, growing conditions, and

diet. Only a small set of enzyme-catalyzed reactions

has thus far been clearly identified with food spoil-

age. Many important deteriorative processes in food

are caused by families of enzymes operating in se-

quence and catalyzing a net change in the tissue, such

as synthesis of lignin in asparagus. Some other

examples of multistep reactions, which contribute

to losses in food quality, are summarized in Table 2.

The detailed mechanisms and biochemical controls

for many of these multistep reactions are not com-

pletely understood. For example, until the advent of

rDNA technology it was generally believed that

the increased solubility of pectin and the associated

texture softening of fruit are caused by hydrolysis of

a-1,4 galacturonate linkages in pectin, a reaction

catalyzed by polygalacturonases (EC 3.2.1.15; EC

3.2.1.67). However, blocking the synthesis of poly-

galacturonases in ripening tomato fruit was not

completely effective in preventing the softening of

transgenic fruit. Since pectin contains small amounts

of other sugar residues in addition to a-1,4 galactur-

onate linkages, it now appears that other, not yet

identified, mechanisms play a role in tomato fruit

softening.

Other Endogenous Enzymes

0005One-step enzyme-catalyzed processes may also

contribute to quality deterioration, particularly in

processed foods. For example, for orange juice, in

which a stable colloidal suspension is desired, the

action of endogenous pectin methylesterase (PME;

EC 3.1.1.11) is undesirable since demethylation of

pectin, catalyzed by this enzyme, leads to separation

of serum from particulates in juice. Heat processing

of orange juice to inactivate PME is undesirable since

a nonenzymatic chemical reaction adversely affects

the delicate flavor of the product. Hydrolases, like

PME, as well as oxidoreductases are the most studied

enzymes in connection with food spoilage. Examples

of enzymes and their contribution to quality loss in

specific commodities are summarized in Table 3.

Nonenzymatic Reactions

0006In the case of heat-treated or other processed food-

stuffs where enzymes have been destroyed or their

activity has otherwise been arrested, nonenzymatic

chemical reactions play a more important role in

food spoilage than enzyme-catalyzed reactions. As

with enzyme-catalyzed reactions some, but not all,

nonenzymatic changes that occur during food pro-

cessing and storage will result in loss of quality.

Examples of nonenzymatic reactions that can lead

to deterioration in food quality are listed in Table 4.

The two nonenzymatic reactions in foods which

appear to be of most widespread importance are

Maillard browning and lipid oxidation. These reac-

tions are discussed in detail in other sections.

Factors Influencing Chemical Reactions in Food

0007The rate of chemical reactions in foodstuffs is a func-

tion of one or more variables, including pH, tempera-

ture, ionic strength, concentration of reactants,

presence of catalysts, mobility of reactants, oxidation

tbl0001 Table 1 Some general characteristics that can distinguish enzymatic and nonenzymatic catalyzed reactions

Treatment Characteristics

Thermal inactivation As proteins, most enzymes are inactivated by a brief heat treatment, while catalysts of nonenzymatic

reactions are normally heat-stable

Dialysis As macromolecules, enzymes are nondialyzable, while catalysts of nonenzymatic reactions are normally

low-molecular-weight and removed by this treatment

Specificity The number of reactants and products in enzymatic reactions are normally less than in the

corresponding nonenzymatic reaction. Enzyme catalysis and inhibition are characterized by

stereospecificity

Proteolysis Enzyme catalysts, as proteins, are often inactivated by treatment with proteolytic enzymes

pH While nonenzymatic reactions are often acid- or base-catalyzed, enzymatic reactions are characterized

by a relatively narrow pH optimum

Temperature coefficient The Q

of nonenzymatic reactions is normally much lower than that of enzymatic reactions

SPOILAGE/Chemical and Enzymatic Spoilage 5503

reduction potential, competing reactions, decompart-

mentation of reactants, and the physical state of the

reaction milieu. One of the most important variables

influencing chemical changes in food is temperature.

The Arrhenius relation gives the influence of tempera-

ture on reaction rate:

k ¼ k

E

=RT

where k is the reaction rate constant, k

is the pre-

exponential constant, E

is the activation energy in

kilojoules per mole, R is the gas constant, and T is the

absolute temperature in Kelvin. E

is normally much

lower for enzymatic reactions than for nonenzymatic

reactions. Thus, in general, the rate of a nonenzy-

matic reaction is more sensitive to temperature

change than is an enzymatic reaction. Enzymes, like

other proteins, are subject to thermal denaturation.

Accordingly, the range of temperature in which cata-

lytic rate increases with a rise in temperature is limited

by the enzyme’s thermal inactivation temperature.

Because of these two considerations, the ‘master’

chemical reaction, i.e., that which limits the storage

tbl0003 Table 3 Some endogenous enzyme-catalyzed reactions that contribute to food spoilage

Enzyme ECnumber Food Importance

Lipoprotein lipase 3.1.1.34 Milk Releases short-chain fatty acids from milk fat leading to hydrolytic

rancidity

Alkaline protease 3.4..24.40 Milk Since this enzyme is stable to heat it may contribute to gelation in

products processed at ultra high temperatures

Thiaminase 2.5.1.2, 3.5.99.2 Shellfish Loss of thiamin in fermented products

Phospholipase 3.1.1.4, etc. Fish Releases fatty acids in frozen product causing denaturation of muscle

proteins and texture deterioration

Trimethylamine oxide

demethylase

4.1.2.32 Fish Releases formaldehyde in frozen gadoid fish that contributes to protein

aggregation and texture deterioration

Lipoxygenase 1.13.11.12, etc. Legume seeds Formation of specific hydroperoxides can lead to bleaching of

pigments, offensive flavor formation, as well as texture change and

loss of nutrients

Peroxidase 1.11.1.1, etc. Vegetables Decomposition of hydroperoxides with generation of free radicals

appears to cause bleaching of pigments, off-flavors, etc.

Ascorbic acid oxidase 1.11.1.11 Citrus Results in loss of vitamin C activity in orange juice

Chlorophyllase 3.1.1.14 Green vegetables Removal of the phytol side chain from chlorophyll appears to be part

of the degreening process during plant senescence

Polyphenol oxidase 1.10.3.1 Fruits, shellfish Enzymatic browning

tbl0002 Table 2 Some multistep enzyme-catalyzed reactions that contribute to food spoilage

Net reaction Contribution to food spoilage

Glucosestarch Loss in sweet taste of some vegetables, e.g., sweetcorn

GlucoseCO

þ H

O Respiration rate is directly related to spoilage rate of fruits, vegetables, and seed crops

Starchglucose þ fructose Cold sweetening of some vegetables leads to excessive Maillard browning, e.g., potato

tuber

Glycogenlactic acid þ H

O Glycogenolysis and glycolysis are of central importance in postmortem myosystems.

The rate and extent of associated pH decline directly (e.g., water-holding capacity, protein

denaturation) and indirectly (e.g., rate of other enzymatic and nonenzymatic reactions)

to influence quality

ATPhypoxanthine The rate and extent of adenosine triphosphate catabolism in myosystems influences meat

quality in several ways, e.g., the acceptability of fish is directly related to the

accumulation of hypoxanthine

Methionineethylene The plant hormone ethylene is synthesized by the ‘methionine cycle’ during specific

developmental change or as a consequence of wound injury. In turn, increased

ethylene can initiate biosynthesis of enzyme cascades, e.g., chlorophyll destruction or

lignin biosynthesis

Insoluble pectinsoluble pectin Texture softening and increased vulnerability to saprophytic microorganisms and physical

damage in some fruits and vegetables, e.g., ripe tomato

Phospholipidaldehydes, ketones,

free radicals

Lipoxygenase cascades can decrease the amounts of essential nutrients, and cause

off-flavors

Collagenpeptides, amino acids Postmortem degradation of collagen is catalyzed by a family of enzymes and can influence

physical integrity, appearance, and yield of fish fillets

5504 SPOILAGE/Chemical and Enzymatic Spoilage

life of a given product, normally differs with the

temperature at which the product is stored (Figure 1).

It is also important to recognize that E

for a given

reaction in a particular temperature range is also a

function of other parameters (e.g., pH, glass transi-

tion). The extent to which other parameters influence

thermal response depends on the particular reaction

under consideration.

0008 The extent and direction to which chemical trans-

formations are influenced by parameters other than

temperature depend on the reaction under consider-

ation. For example, removal of oxygen from fish tissue

decreases the rate of enzymatic or nonenzymatic lipid

oxidation and the development of off-flavors, but

at the same time it increases the rate of enzymatic

trimethylamine oxide (TMAO) demethylation and

associated protein aggregation. Likewise, reducing

the water concentration of food by dehydration may

decrease the mobility of water-soluble reactants, but

it does not serve the same function for fat-soluble

reactants and may even promote lipid oxidation by

exposing lipid substrates to oxygen and increasing the

availability of a metal catalyst.

0009It is also important to consider that, food-processing

and storage conditions, designed to minimize one

detrimental reaction, may inadvertently alter other

tbl0004 Table 4 Some nonenzymatic reactions that can lead to loss in food quality

Reactant(s) Product orresult Importance

Chlorophyll, H

Pheophytin, Mg

2þ

Loss of Mg

2þ

from chlorophyll results in olive-brown

discoloration of green vegetables. Reaction occurs rapidly at low

pH and high temperature

All-trans b-carotene Tr a n s –cis rearrangement Isomerization of carotenoids is promoted by light or heat and results

in isomers, which absorb light in shorter wavelength and with

lower extinction coefficients, and loss of provitamin A activity

Cysteine H

S, NH

, acetaldehyde Thermal degradation of sulfur-containing amino acids can directly

produce aroma and also lead to other reactions involving the

products

RCHO, RNH

Maillard browning The Maillard reaction is one of the most important reactions in foods,

affecting color, flavour, nutrition, and possibly safety

Amylose Crystallization The alignment of linear starch chains by hydrogen bonding to form

insoluble precipitates, a process called retrogradation, is important

in processed products containing gelatinized starch,

e.g., bread staling

Anthocyanin, SO

Decolorization The addition of SO

to the 4-position of anthocyanins to form a

bisulfite addition product results in loss of color

Organic acid, Ca

2þ

Ca-chelate Organic acids like phytic acid or citric acid can destabilize

polygalacturonate in the middle lamella by sequestering Ca

2þ

and

thereby influence texture

Ascorbic acid 2-Furaldehyde, CO

The nonenzymatic degradation of vitamin C occurs by an acid/metal

ion-catalyzed reaction or by an oxidative mechanism. In addition

to loss in nutritive value, carbonyl degradation products, such as

diketogulonic acid, can contribute to Maillard browning

Fatty acid, O

Autooxidation Autooxidation is a free radical reaction which can be catalyzed by

metal ions; the reaction rate increases with degree of unsaturation;

a primary effect on quality is formation of off-flavors; however,

all quality indices, including nutrition, color, texture and safety

may be influenced under appropriate conditions

Protein Denaturation Loss of protein native structure can lead to protein aggregation and

loss in functional properties with the possibility of influence on all

quality indices under appropriate reaction conditions

Myoglobin,

thiol compound, TMAO

Green tuna Precooking tuna containing a high content of trimethylamine oxide

(TMAO) can lead to green discoloration of tuna by an oxidation

reduction reaction

Aspartame, peptides, nitrite Mutagenic compounds Naturally occurring dipeptides and the artificial sweetener aspartame

can form mutagenic compounds after nitrosation. Aspartame is also

unstable under alkaline conditions and heat

Arginine 1-Methylguanidine High-temperature (e.g., 150–210



C) treatment of arginine results in

formation of mutagenic compounds, such as those found in cooked

grain-based foods

Thiamine, H

or OH



2-Methyl-4-amino 5-aminethyl

pyrimidine, etc.

Vitamin B

is destroyed by various reactions, including acid- or

base-catalyzed reactions, redox reactions, photolysis, and reaction

with bisulfite

SPOILAGE/Chemical and Enzymatic Spoilage 5505

parameters which, in turn, may function to promote

the same detrimental reaction. For example, while

freezing of food lowers temperature and water activ-

ity, and thus is expected to lower the rate of reaction,

it may serve otherwise to accelerate the rate by unex-

pected changes in pH, ionic strength, or reactant

availability.

0010 Moreover, storage or processing strategy designed

to minimize a reaction that adversely affects storage

life may accelerate other reactions that cause a differ-

ent, but equally unacceptable, quality. For example,

pasteurization of kiwi fruit juice (pH 3.5) inactivates

enzymes and spoilage organisms that contribute to

spoilage; but at the same time, heat treatment causes

rapid pheophytinization of chlorophyll and loss in the

characteristic green color of the product. Because of

the complexity of food systems it is often difficult to

predict the consequences of processing and storage

conditions on quality. Accordingly, efforts to minim-

ize the contribution of chemical reactions to food

spoilage require an empirical approach, at least in

part.

See also: Browning: Nonenzymatic; Enzymatic –

Biochemical Aspects; Enzymatic – Technical Aspects and

Assays; Enzymes: Functions and Characteristics; Uses in

Food Processing; Spoilage: Bacterial Spoilage