Food Biochemistry and Food Processing (2 edition)

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9 Enzymes in Food Processing 199

monosaccahride units such as xylose, mannose, galactose,

rhamnose, and arabinose, and sugar acids such as mannuronic

acid and galacturonic acid); and the enzyme naringinase is used

for bitterness reduction in citrus fruit juice (e.g., grapefruit

juice) processing.

Tea, cocoa, and coffee contain varying levels of caffeine and

its related compound theobromine. Thus, intake of beverages

derived from these plant materials elicits a stimulant effect in the

consumer. Enzymes like polyphenoloxidases and peroxidases

promote oxidation and browning reactions during “fermenta-

tion” of these products (tea, coffee, and cocoa) as part of the

overall darker colors normally associated with these products;

in the particular case of coffee, the dark color is enhanced by the

roasting of the beans. Amylases are used in cocoa and chocolates

to liquefy starches to permit free flow, and in the case of teas,

the enzyme tannase breaks down tannins to enhance the solu-

bilization of tea solids. Other enzymes such as invertase, LOX,

peroxidases, and proteases also play an important role in flavor

development in the beverages derived from these products.

The enzyme GOX is also used to remove head-space O 2 from

bottled beverages.

Enzymes in Candies and Confectioneries

Various hydrolytic enzymes are used as processing aids for the

manufacture of chocolate-covered soft cream candies, e.g., amy-

lases and invertase, and for the recovery of sugars from candy

scraps, e.g., amylases, invertase, and proteases (Cowan 1983).

A mixture of cellulases, invertase, pectinases, and proteases are

used in making candied fruits (Mochizuki et al. 1971). Amy-

lases are also used to produce high-maltose and high-glucose

syrups for use as sweetener in the manufacture of hard candies,

soft drinks, and caramels. Lipases are used to modify butterfat

to increase buttery flavors in candies and caramels and to reduce

sweetness as well (Burgess and Shaw 1983).

Enzymes in Animal Feed and Pet Care

Agricultural (used here to encompass plant, livestock, and fish)

harvesting and processing discards are high in useful nutrients

such as carbohydrates (both starch and nonstarch types), pro-

teins, and lipids, some of which cannot be fully digested and

utilized directly by animals. In general, the discards are used

as feed for animals. Different kinds of enzymes are added to

these source materials to modify them into forms that are more

amenable to digestion and utilization for improved feed effi-

ciency. Examples of enzymes used for this purpose include mi-

crobial amylases, cellulases, glucanases, xylanases, phytases,

and proteases, to degrade simple and complex carbohydrates,

as well as proteins. Cellulases and pectinases also play an im-

portant role in silage production, while alkaline proteases (from

bacteria and fungi) are employed for enzymatic decolorization

of whole blood from abattoirs for use as animal feed protein.

The enzymatic action results in an increase in available metab-

olizable energy and protein utilization, reduced viscosity, and

liberation of bound phosphorous.

Enzymes are also used in pet care to provide relief from the

effects of dry or scaly hair coats, skin problems, digestive and

immune disorders, weight problems, allergies, bloating, and

other disorders that afflict household pets. Enzymes are also

used to enhance wound healing and rectify soreness, pain, and

inflammations suffered by highly active as well as arthritic pets.

A summary of various foods produced commercially (and/or

in households) via enzyme-assisted transformations is provided

in Table 9.2.

CONTROLLING ENZYMATIC ACTIVITY

IN FOODS

The action of enzymes in foods may not always be desirable. For

example, continued enzymatic activity in foods after they have

been used to attain the desired transformation could adversely

affect food quality. The natural presence of certain enzymes in

agricultural materials (e.g., LOX, PPO, peroxidases, and lipases)

may induce undesirable changes (e.g., color loss, dark discol-

orations, and rancidity) in foods; the action of some naturally

occurring enzymes (e.g., histidine decarboxylases) may produce

toxic compounds (biogenic amines) in food products; and yet

other enzymes (e.g., thiaminase and ascorbic acid oxidase) may

act to destroy essential food components (e.g., vitamins B 1 and

C). Thus, it is necessary to control enzymatic activity in food

stuffs to obviate the potential deleterious effects they cause in

these products. There are several factors that are known to af-

fect enzyme activity and influence their behavior in foods. The

factors include temperature, pH, water activity (Aw), and chem-

icals (inhibitors, chelating agents, and reducing agents), and

advantage is taken of this fact by food technologists and food

manufacturers to develop or rationalize procedures to control

enzymatic activity in foods.

Temperature Effects

Temperature can affect the activity and stability of enzymes (as

well as the substrate the enzymes act on). Thus, temperature

effects on enzyme activity are mixed. Temperatures modulate

the motion of biomolecules (both enzymes and their substrates)

as well as interactions between molecules.

Heat Treatments

An increase in temperature (up to the temperature optimum of

the enzyme) generally elevates the average kinetic energy of en-

zyme molecules and their substrates, and manifests as increased

rates of enzyme catalyses. However, beyond the optimum tem-

perature, further increases in temperature do not increase the av-

erage kinetic energy of molecules, rather they disrupt the forces

that maintain the conformation and structural integrity of the

molecules that are crucial for their stability and normal catalytic

activity. Under those circumstances, enzyme molecules undergo

denaturation, inactivation, and lose catalytic activity. The heat

denaturation may be reversible or irreversible depending on the

severity and/or duration of the heat treatment. Advantage is

taken of this heat inactivation of enzymes in processes such as