AGGREGATION OF PROTEINS IN WHEY FROM RAW AND HEAT-PROCESSED MILK - FORMATION OF SOLUBLE MACROAGGREGATES AND NUTRITIONAL CONSEQUENCES

Whey proteins were isolated from raw, pasteurized UHT and sterilized m ilk after isoelectric precipitation. Protein macroaggregates were remo ved from total whey extracts by filtration through a 0.45 mu m membran e. The protein content of I raw extracts and of the filtrate was monit ored by SDS-PAGE and SE-HPLC, and found to decrease as a function of t he thermal treatment. The amino acid composition, surface hydrophobici ty parameters ann disulphide chemical reactivity were also determined the results obtained indicated that macroaggregates not included in th e filtrate were stabilized by hydrophobic interactions and disulphide bonds. The in vitro protein digestibility of total whey extracts was p rogressively impaired as a function of the intensity of the heat treat ment of milk, and was lower in total extracts compared to the correspo nding filtrates, suggesting that the accessibility to proteolytic enzy mes of whey proteins was dependent on the extent of aggregation. (C) 1 998 Academic Press.