Food Biochemistry and Food Processing

468 Part IV: Milk

This can be recovered by crystallization from a con-
centrated (supersaturated, 60–62% TS) preparation
of either whey or whey permeate (for review see
Muir 2002). The crystalline lactose is usually recov-
ered using a decanter centrifuge, dried in a fluidized
bed dryer, and ground to a fine powder, which is
used in food applications, for example, confection-
ery products and infant formulas. Lactose is also
used widely in pharmaceutical applications (e.g., as
a diluent in drug tablets); for such applications, the
lactose is generally further refined by redissolution
in hot water and mixing with activated carbon, fol-
lowed by filtration, crystallization,and drying.
Many derivatives of lactose can be produced;
these derivatives are more valuable and useful than
lactose (Fig. 20.3).

MILK PROTEINS: ISOLATION,
FRACTIONATION, AND
APPLICATIONS

In recent years, it has been increasingly recognized
that milk proteins have functionalities that can be
exploited in food systems other than conventional
dairy products; these proteins have been increasing-
ly recognized as desirable ingredients for a range of
food products (Mulvihill and Ennis 2003). The very
different properties of the two classes of milk pro-
teins, the caseins and the whey proteins, present dif-

ferent technological challenges for recovery and are

suitable for quite different applications. The whey

proteins were discussed in Whey Processing section,

and the caseins are discussed below.

RECOVERY ANDAPPLICATION OFCASEINS

Technologies for the recovery of caseins from milk

are based on the fact that relatively simple perturba-

tions of the milk system can destabilize the caseins

selectively, resulting in their precipitation and facili-

tating their recovery from milk (Mulvihill and Fox

1994, Mulvihill and Ennis 2003). As discussed in the

Coagulation subsection (under Rennet-Coagulated

Cheeses), the stability of the caseins in a colloidal

micellar form is possible due to the amphiphilic na-

ture of -casein. To overcome this stability and pre-

cipitate the caseins merely requires destruction of

this stabilizing effect.

The two key principles used to destabilize the

micelles are (1) acidification to the isoelectric point

of the caseins (pH 4.6) or (2) the addition of en-

zymes, for example, chymosin, which hydrolyze -

casein, removing the stabilizing glycomacropeptide.

In both cases, the starting material for casein pro-

duction is skim milk. For acid casein, acidification

can be achieved either by addition of a mineral acid,

usually HCl, or fermentation of lactose to lactic acid

by a culture of lactic acid bacteria. When the iso-

Figure 20.3.Food-grade derivatives of lactose.