ISOLATION OF LIPASE-ACTIVE FRACTIONS FROM ULTRA-HIGH TEMPERATURE PROCESSED MILK AND THEIR PATTERNS OF RELEASING FATTY-ACIDS FROM MILK-FAT EMULSION

To examine residual lipase activities in UHT-processed milk Samples, t wo protein isolates were prepared, one from aqueous supernatant and th e other from milk fat globule membrane. Results of DEAE-cellulose chro matography indicated that the protein isolates from the aqueous supern atants contained three lipase-active fractions; the proteins from the milk fat globule membranes exhibited only one lipase-active fraction. Analysis by SDS-PAGE revealed that the lipase-active fractions from th e aqueous supernatants contained a major or minor kappa-casein compone nt, as well as other caseins and whey proteins. However, the lipase-ac tive fraction from the milk fat globule membranes was composed mainly of alpha-casein. When a pool of the lipase-active fractions from the a queous supernatants was incubated with a milk fat emulsion at 35-degre es-C for 4 h, the fractions hydrolyzed butyric acid the most, followed by caproic and palmitic acids. However, the lipase-active fraction fr om the milk fat globule membranes hydrolyzed palmitic and stearic acid s most, followed by linoleic and oleic acids.