Dairy Chemistry And Biochemistry

MILK PROTEINS^227

the column, p-lg, which has a higher affinity for this resin than the other

proteins, displaces a-la and BSA, giving a mixture of these proteins in the

eluate; a highly purified p-lg can be obtained by eluting the protein-

saturated column with dilute HCl.

4.15.7 Casein-whey protein co-precipitates

Following denaturation, the whey proteins coprecipitate with the caseins on

acidification to pH 4.6 or addition of CaCI, at 90°C, to yield a range of

products known as casein-whey protein co-precipitates (Figure 4.43). The

main attraction of such products is an increase in yield of about 15%, but

the products also have interesting functional properties. However, they have

not been commercially successful.

New forms of co-precipitate, referred to as soluble lactoprotein or total

milk protein, with improved solubility, have been developed recently (Figure

4.44). By adjusting the milk to an alkaline pH before denaturing the whey

proteins and co-precipitating them with the caseins at pH 4.6, the function-

Skim milk

CaCI, addition 0.03%

I

1

Heating 9OoC x 15 rnin

conditions

Precipitation Acidify to

conditions p~ 4.6

I

Low Ca

co-precipitate

0.06%

9OoC 10 rnin

Aci a ify to

pH 5.4

Medium Ca

cc-precipitate

90°C^1 x 2 rnin

CaCI, to

0.20'"

High Ca

co-precipita te

t

NaOH

I

Na salts of co-precipitates

Figure 4.43 Protocols for the manufacture of conventional casein-whey protein co-precipitates
(from Mulvihill, 1992).