COMPOSITION OF MOLECULAR-SPECIES OF TRIACYLGLYCEROLS IN BOVINE-MILK FAT

Triacylglycerols from bovine milk fat were fractionated by reversed-ph ase liquid chromatography. The fatty acid and triacylglycerol composit ions of each fraction were determined by capillary gas chromatography. These data were used to determine the accurate proportions of 223 ind ividual molecular species of even-numbered triacylglycerols, accountin g for 80% of total triacylglycerols (all percentages are expressed as moles per 100 mol). The three major triacylglycerols were butyroylpalm itoylacylglycerols, namely butyroylpalmitoyloleoylglycerol (4.2%), but yroyldipalmitoylglycerol (3.2%), and butyroylmyristoylpalmitoylglycero l 3.1%). Twenty-two triacylglycerols (>1%) contained at least two of t he four major long-chain fatty acids (C-14:0, C-16:0, C18:0, and C18:1 ). Among them were eight butyroyldiacylglycerols, the proportions of w hich reached 19% in total but only 12% when calculated on the basis of a random distribution of the fatty acids in the triacylglycerol molec ules. More generally, most of the triacylglycerols that are composed o f a short-chain fatty acid (C4:0 or C6:0) and two fatty acids in the r ange of C-12 to C18 are preferentially synthesized by the mammary glan d; their proportions (36% in total) were higher than the corresponding random values (24% in total). Conversely, the total amounts of simple (.4%) and mixed (2.9%) saturated long-chain (C-14:0 to C18:0) triacyl glycerols were much lower than those expected from random calculation (1.9 and 6.1%, respectively).