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9 Enzymes in Food Processing 183immobilized onto stationary support materials to permit their
reuse and thereby reduce processing costs. Most of them are
quite heat labile; thus, they can be readily inactivated by mild
heat treatments after they have been used to achieve the de-
sired transformation in foods, and they are natural and relatively
innocuous components of agricultural materials that are consid-
ered “safe” for food and other nonfood uses (e.g., drugs and
cosmetics). Their action on food components other than their
substrates are negligible, and more gentle, thus resulting in the
formation of purer products with more consistent properties;
and they are also more environmentally friendly and produce
less residuals (or processing waste that must be disposed of at
high costs) compared to traditional chemical catalysts (van Oort
2010). Because of these beneficial effects, enzymes are used in
the food industry for a plethora of applications including: baking
and milling, production of (both alcoholic and nonalcoholic bev-
erages), cheese and other dairy products manufacture, as well
as the manufacture of eggs and egg products, fish and fish prod-
ucts, meats and meat products, cereal and cereal products, and
in confectionaries.Undesirable EffectsCertain food enzymes cause undesirable autolytic changes in
food products, such as excessive proteolysis to produce bitter-
ness in cheeses and protein hydrolysates, or excessive texture
softening in meats and fish products (e.g., canned tuna). En-
zymes like proteases, lipases, and carbohydrases break down
biological molecules (proteins, fats, and carbohydrates, respec-
tively) to adversely impact flavor, texture, and keeping quali-
ties of the products. Decarboxylases and deaminases degrade
biomolecules (e.g., free amino acids, peptides, and proteins)
to form undesirable and/or toxic components, e.g., biogenic
amines, in foods. Some others, for example, polyphenol oxi-
dases (PPO) and lipoxygenases (LOX), promote oxidations and
undesirable discolorations and/or color loss in fresh vegetables,
fruits, crustacea, and salmonids, and others like thiaminase and
ascorbic acid oxidase cause destruction of essential components
(vitamins) in foods. Thus, more effective treatments must be de-
veloped and implemented to safeguard against such undesirable
effects of enzymes in foods.SOURCES OF FOOD ENZYMES (PLANT,
ANIMAL, MICROBIAL, AND
RECOMBINANT)Enzymes have been used inadvertently or deliberately in food
processing since ancient times to make a variety of food prod-
ucts, such as breads, fermented alcoholic beverages, fish sauces,
and cheeses, and for the production of several food ingredients.
Enzymes have been traditionally produced by extraction and
fermentation processes from plant and animal sources, as well
as from a few cultivatable microorganisms.
Industrial enzymes have traditionally been derived from plant,
animal, and microbial sources (Table 9.1). Examples of plant en-
zymes includeα-amylase,β-amylase, bromelain,β-glucanase,ficin, papain, chymopapain, and LOX; examples of animal en-
zymes are trypsins, pepsins, chymotrypsins, catalase, pancreatic
amylase, pancreatic lipase, and rennet; and examples of mi-
crobial enzymes areα-amylase,β-amylase, glucose isomerase,
pullulanase, cellulase, catalase, lactase, pectinases, pectin lyase,
invertase, raffinose, microbial lipases, and proteases.
Microorganisms constitute the foremost enzyme source be-
cause they are easier and faster to grow and take lesser space
to cultivate, and their use as enzyme source is not affected by
seasonal changes and inclement climatic conditions and are thus
more consistent. Their use as sources of enzymes is also not
affected by various political and agricultural policies or deci-
sions that regulate the slaughter of animals or felling of trees
or plants. Industrial microbial enzymes are obtained from bac-
teria (e.g.,α-andβ-amylases, glucose isomerase, pullulanase,
and asparaginase), yeasts (e.g., invertase, lactase, and raffinose),
and fungi (e.g., glucose oxidase (GOX), catalase, cellulase, dex-
tranase, glucoamylase, pectinases, pectin lyase, and fungal ren-
net). Even though all classes of enzymes are expected to occur
in all or most microorganisms, in practice, the great majority
of industrial microbial enzymes are derived from only a very
few GRAS (generally recognized as safe) species, the predomi-
nant ones being types likeAspergillusspecies,Bacillusspecies,
andKluyveromycesspecies. This is because microorganisms can
coproduce harmful toxins, and therefore need to be stringently
evaluated for safety at high cost before they can be put to use
for food production. As such, there are only very few microor-
ganisms currently used as safe sources of enzymes and most of
these strains have either been used by the food industry for sev-
eral years or been derived from such strains by genetic mutation
and selection.
The traditionally produced enzymes are invariably not well
suited for efficient use in food-processing applications for rea-
sons such as sensitivity to processing temperature and pH, in-
hibitory reaction components naturally present in foods, as well
as availability, consistency, and cost. Recent developments in
industrial biotechnology (including recombinant DNA and fer-
mentation technologies) have permitted molecular biologists
and food manufacturers to design and manufacture novel en-
zymes tailor-made to suit particular food-processing applica-
tions (Olempska-Beer et al. 2006). These new microbial en-
zymes are adapted to have specific characteristics that make
them better suited to function under extreme environmental con-
ditions, e.g., pH and temperature. The production of recombinant
enzymes by recombinant DNA technology entails the introduc-
tion of the genes that encode for those enzymes from traditional
sources into special vectors to produce large amounts of the
particular enzyme. Recombinant enzymes are useful because
they can be produced to a high degree of purity, and they can
be produced in high yields and made available on a continu-
ing and consistent basis at much reduced cost. As well, their
purity and large-scale production reduce extensive quality as-
surance practices; and the technique itself enables useful (food)
enzymes from unsafe organisms to be produced in useful forms
as recombinant enzymes in safer microorganisms.
Examples of recombinant enzymes available for food use
include various amylases, lipases, chymosins, and GOX.