Structure and Synthesis of Milk Fat. V. A Postulated Sequence of Events from Analyses of Mammary Tissue Lipids1,2

Abstract

Listen

Translate article

Summary To further reveal the structure and synthesis of milk fat, mammary tissue lipids from two goats and two cows, all lactating, were analyzed. In comparison to the composition of milk lipids, the mammary tissue lipids showed elevated levels of all lipid classes excepting triglycerides. The investigation centered on fatty acid composition of the di- and triglycerides of mammary tissue, and milk fat from the section of udder corresponding to the tissue lipid sample. The objective was to shed light on intermediates in triglyceride and fat globule formation. It was found that the substantial levels of diglycerides (2–6%) in the mammary tissue lipids have the 1,2-configuration. These diglycerides are low in short-chain fatty acid content (particularly butyrate) in comparison to the triglycerides of the tissue and to milk fat. The evidence suggests that the diglycerides are intermediates in triglyceride formation rather than artifacts of lipolysis. A consideration of butyrate levels in the various glyceride fractions leads to the conclusion that in the main it occurs only one mole per mole of triglyceride and its incorporation is a completing step in triglyceride formation. The mammary tissue lipids appear to be mainly, if not entirely, milk lipids in process. When the triglycerides of the tissue are considered in this light, and in light of evidence from mammary tissue morphology studies, further refinements in the conception of milk fat synthesis can be made and are presented.