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Effect of Certain Factors upon Lipolysis in Homogenized Raw Milk and Cream^*

Department of Dairying, Michigan State College, Mast Lansing, Michigan

ABSTRACT

The results secured in this study show that lipase action which occurs in homogenized raw milk usually reacts to external factors differently than does the lipase in normal milk. Other workers (1, 5, 8) have shown normal lipase activity to be greatly inhibited by copper, whereas in the studies herein presented, no such influence was detected in homogenized raw milk. Further, the work of Davies (1), and Krukovsky and Sharp (8) indicates oxidative changes occur simultaneously with, or perhaps precede, normal lipase action, but in these studies on "homogenization" lipolysis, no oxidative changes could be detected by means of the peroxide determinations, even though large amounts of fat splitting had occurred.

The fact that formalin had no inhibiting effect on lipolysis in homogenized raw milk would indicate that the lipase action in this product is different from that of normal milk, since Herrington and Krukovsky (5) found that formalin markedly lowers the lipase action in normal milk. However, Tarassuk (12) reported a study of milk from one cow in which formalin did not influence the activity of the lipase. On the basis of their formalin studies, Herrington and Krukovsky (5) expressed the belief that there are two lipases in milk, one of which is not affected by formalin. Dorner and Widmer (2) had previously suggested the presence of two lipases, one of which is extremely heat labile and which produces a sharp, bitter taste and marked acidity changes. These findings may indicate that the iipase in homogenized milk is different from the one responsible for the major portion of lipolytic activity in normal milk. However, additional proof of this is needed before definite conclusions may be drawn.

Further results of this study show that increasing the NaCl content decreases the lipolysis, whereas the lipase activity is increased by increases in the storage temperatures. Heating of the cream and skim milk fractions indicates that the lipase agent follows the plasma phase. Further, the lipolysis in a prepared fat-skim milk product was greater than in a similarly prepared mixture of fat and whey, although the fat dispersed in the whey did undergo appreciable splitting.

^* Journal Article 518 (n. s.) from the Michigan Agricultural Experiment Station.