Rapid and Sensitive Assay for Milk Lipase

Abstract

An improved micromethod has been developed for measuring lipase activity in milk by the pH stat technique. The silica-gel procedure measures only 16.8% of the lipase activity observed in milk by the pH stat method. The major factors contributing to this apparent low lipase activity by the silica-gel method were a) incomplete titration of the long chain free fatty acids; b) lack of proportionate response of milk lipase activity to increased concentrations of milk in the assay system; and c) variations in the pH of the lipase assay mixture during the silica-gel incubation period. Compared to the silica-gel method, the pH stat assay had greater sensitivity, accuracy, and rapidity and allowed measurement of the initial reaction velocity. During storage at 4 C the lipolytic activity of fresh raw milk was constant up to 24 hr, after which it decreased. Homogenization of raw milk does not appear to affect lipase activity per se.It appears to be a substrate activating phenomenon, in that there is a direct relationship between homogenization pressure and susceptibility of milk fat to lipolysis. © 1966, American Dairy Science Association. All rights reserved.