Lipase redistribution in cows' milk during induced lipolysis. II. Activation by milk pH adjustment

Cold-stored milk lipolysis was enhanced from 5- to 50-fold when milk pH was adjusted to 7-8 with NaOH, while it was greatly decreased or stopped by an adjustment to pH 6-5.5 with citric acid. Small adjustments in pH (less than or equal to 0.5 pH unit) also affected lipolysis, but the pH of native milk was not related to spontaneous lipolysis. The binding of lipoprotein lipase to cream was a pH-dependent process with an optimum near pH 7.0. Activity of the cream lipase on cold-stored milk fat continuously increased from pH 6.6 to pH 8.5. The activating effect of heparin on cold-stored milk lipolysis reached a maximum at pH 7.0-8.0 and a minimum in native milk, while addition of blood serum gave an opposite response.