Studies on the Bile Salt Stimulated Lipolytic Activity of Human Milk Using Whole Milk as Source of Both Substrate and Enzyme. I. Nutritional Implications
Summary: The lipolytic activity of human milk was assayed using whole fresh milk as source of both enzyme and substrate. Bile salts and specifically glycine rather than taurine conjugates were essential for activity; a concentration of 2 mM being optimal. The lipid concentration and lipolytic activity increased significantly (P < 0.01 and < 0.02 respectively) during the course of a feed. The lipid concentration and lipolytic activity were compared in immature and mature milks (less and greater than 15 days postpartum respectively). The lipolytic activity remained constant whereas the lipid concentration was significantly greater in the mature than the immature milks (P < 0.001). In none of the milks was the substrate concentration limiting. The % hydrolysis of ingested triglyceride in the immature and mature milks was calculated to be approximately 40 and 20% respectively in 2 h, which is the estimated transit time from the duodenum to ileum. The major lipolytic products were free fatty acids and in general the enzyme showed little specificity for different fatty acids of triglyceride. Speculation: The characteristics of the bile salt stimulated lipase activity of human milk suggest that it is involved in the digestion of milk fat in the small intestine of the infant and that it complements rather than duplicates pancreatic lipase activity. The activity maintained throughout lactation suggests that this lipase plays an important nutritional role in the newborn.