Proteins

A large variety of food proteins, either from animal

(milk, meat, eggs, blood, fish) or plant (seeds, cereals)

origin, are available in the food industry. To illustrate

the discussion on the determination of proteins in food

and food products, an important representative from

each product class was chosen, i.e., milk proteins for

animal species and cereal proteins for plants. In Tables

1 and 2 an overview is given of the molecular structure

and basic properties of the major protein fractions

present in both substrates. Specific attention is drawn to those properties that

might be of importance for the determination in food

and food products. Milk proteins are subdivided into

random coiled caseins, which precipitate on acidifica-

tion of raw skim milk to pH 4.6 at 20C, and into globular whey proteins, which remain in the serum.

Cereal proteins are primarily composed of prolami-

nes (e.g., gliadins for wheat, zeins for maize, hordeins

for barley, and avenins for oats) and glutelins (e.g.,

glutenins for wheat), which can be isolated from cereal

grains and flours by means of the classical Osborne

fractionation procedure (1,2). More detailed informa-

tion on both types of food proteins can be found in

Ref. 3. Apart from their nutritional value, food proteins

serve as important functional ingredients in food and

food products. Functional properties are defined as

those physical and chemical properties that affect the

behavior of proteins in food systems during processing,