Dairy Ingredients for Food Processing

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Chapter 12

Enzyme - modifi ed Dairy Ingredients

Arun Kilara and Ramesh C. Chandan

Introduction

Enzymes are biocatalysts. Catalysts speed up
reaction rates without undergoing permanent
changes, and biological catalysts are impor-
tant in all life processes. It is an axiom that
life itself would not exist if not for enzymes.
The operating characteristics of enzymes
include substrate specifi city, optimum tem-
perature, optimum pH, and other environ-
mental factors. Almost all known enzymes
are proteins and range in size from 13,000 to
several million Da. Only a few residues
within a structure of the enzyme are impor-
tant for the catalytic activity.
Commercial enzymes are derived from
animal, plant, and microbial sources.
Although the International Union of Bio-
chemists recommends scientifi c classi fi cation
of enzymes, colloquial names predominate in
the food industry. Most enzyme names end
in “ – ase ” and are derived from the source of
the enzyme or the substrates which they act
on. Hence, enzymes acting on proteins are
called proteases, those acting on lipids,
lipases; and carbohydrates, carbohydrases.
Among proteases, enzymes derived from
plants such as those from papaya ( Carica
papaya ) are called papain; from fi g latex,
fi cin; or from pineapples, bromelain. Clearly,
these proteases do not end in “ ase, ” refl ecting
the vagaries of colloquial nomenclature of

enzymes. Animal - derived enzymes come

from the organs of domesticated farm

animals; trypsin, chymotrypsin, pre - gastric

lipase, pancreatin, and the like are commonly

isolated from porcine or caprine sources.

Both animal and plant sources of enzymes

impose severe constraints on the production

of large quantities of enzymes. Therefore,

with the advent of biotechnology, microbial

enzymes prevail.

Microbial enzymes for commercial use

are extracted from yeasts, molds, or bacteria.

They are contained within the cells or secreted

into the growth medium. Enzymes contained

within the cells are termed endocellular,

whereas those secreted into the growth

medium are extracellular. Extracellular

enzymes are generally low - molecular - weight

proteins (30 to 50 kilodaltons) and contain

disulfi de bridges. Endocellular enzymes reg-

ulate the metabolism of organisms (regula-

tory enzymes) and are of higher molecular

weights, and often their structures involve

subunits.

Materials on which enzymes act are called

substrates. Those of interest in the dairy

industry are proteins, lipids, and lactose. As

detailed in Chapter 2 , milk proteins are clas-

sifi ed as caseins and serum proteins. Milk fat

consists of triglycerides and a number of

other lipid substances. Lactose is the main

carbohydrate in milk.

Enzymes transform fl uid milk to products.

For example, treating milk with the enzyme

lactase yields low - lactose milk suitable for

consumption by people unable to digest

Dairy Ingredients for Food Processing edited by
Ramesh C. Chandan and Arun Kilara
© 2011 Blackwell Publishing Ltd.