Dairy Chemistry And Biochemistry

MILK PROTEINS 147

10 -

0: I I I

0 10 20 30

Days postpartum

Figure 4.2 Changes in the concentration of total protein (A) and of casein (0) and whey

proteins (W) in bovine milk during the early stage of lactation.

from c. 1 to c. 24% (Table 4.1). The protein content of milk is directly related
to the growth rate of the young of that species (Figure 4.3), reflecting the
requirements of protein for growth.
The properties of many dairy products, in fact their very existence,
depend on the properties of milk proteins, although the fat, lactose and
especially the salts, exert very significant modifying influences. Casein
products are almost exclusively milk protein while the production of most
cheese varieties is initiated through the specific modification of proteins by
proteolytic enzymes or isoelectric precipitation. The high heat treatments to
which many milk products are subjected are possible only because of the
exceptionally high heat stability of the principal milk proteins, the caseins.
Traditionally, milk was paid for mainly on the basis of its fat content but
milk payments are now usually based on the content of fat plus protein.
Specifications for many dairy products include a value for protein content.
Changes in protein characteristics, e.g. insolubility as a result of heat
denaturation in milk powders or the increasing solubility of cheese proteins
during ripening, are industrially important features of these products.
It is assumed that the reader is familiar with the structure of proteins; for
convenience, the structures of the amino acids found in milk are given in