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, two protein isolates were prepared, one from aqueous supernatant and the other from milk fat globule membrane.Results of DEAE-cellulose chromatography indicated that the protein isolates from the aqueous supernatants 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 the aqueous supernatants contained a major or minor K-casein component, as well as other caseins and whey proteins.However, the lipase-active fraction from the milk fat globule membranes was composed mainly of a-casein.When a pool of the lipase-active fractions from the aqueous supernatants was incubated with a milk fat emulsion at 35°C for 4 h, the fractions hydrolyzed butyric acid the most, followed by caproic and palmitic acids.However, the lipase-active fraction from the milk fat globule membranes hydrolyzed palmitic and stearic acids most, followed by linoleic and oleic acids.