Utilisation of Milk Components: Casein

Abstract

Whey may be defined, broadly, as the serum or watery part of milk remaining after separation of the curd that results from the coagulation of milk by acid or proteolytic enzymes. Its composition will vary substantially, depending on the variety of cheese produced or the method of casein manufacture employed. On average, whey contains about 65 g kg-1 of solids, comprising about 50 g lactose, 6 g protein, 6 gash, 2 g non-protein nitrogen and 0·5 g fat. The protein fraction contains about 50 per cent fJ-Iactoglobulin, 25 per cent a-lactalbumin and 25 per cent other protein fractions including immunoglobulins. There are wide variations in composition depending on milk supply, and the process involved in production of the whey. Wheys can be conveniently classed into groups: Sweet wheys: titratable acidity 0·10-0·20 per cent pH typically 5·8-6·6. Medium acid wheys: titratable acidity 0·20-0·40 per cent, pH typically 5·0-5·8. Acid wheys: titratable acidity greater than 0·40 per cent, pH> 5·0. In general, wheys produced from rennet-coagulated cheeses develop low levels of acidity, whereas the production of fresh acid cheeses, such as Ricotta or Cottage cheese, yields medium acid or acid wheys. Whey from caseins produced by acid addition is classed as high acid whey, whereas whey from rennet casein is sweet whey. Typical pH values and titratable acidities for a range of wheys are shown in Table I.