Positional analyses of triacylglycerol fatty acids in the milk fat of the antarctic fur seal (Arctocephalus gazella).

The positional distribution of fatty acids has been determined for the milk triacylglycerols of the Antarctic fur seal, Arctocephalus gazella. Of particular interest was the positional distribution of the polyunsaturated n-3 fatty acids in milk triacylglycerols (TG). In adipocytes of pinnipeds, TG are synthesized with the n-3 fatty acids primarily in the sn-1,3 positions. To determine the positional distribution, extracts of enzymatically digested lipids were separated by thin-layer chromatography, and the constituent fatty acids were separated and quantified by gas-liquid chromatography. Monoenoic and saturated fatty acids comprised over 75% of the total, the ratio of monoenoic to saturated fatty acids being 2:1. The percent content of the long-chain n-3 fatty acids, 20:5, 22:5 and 22:6, ranged between 15-20%. The positional analyses revealed that at the sn-2 position of milk TG, saturated fatty acids were in excess (57%), and the content of n-3 fatty acids was less than 5%. More than 80% of the n-3 fatty acids in milk were located in the sn-1,3 positions. The data indicate that in pinnipeds TG are synthesized in the mammary gland and adipose tissue with fatty acids having similar positional distributions.