A study of the triglyceride structure of bovine milk fat : a thesis

Pancreatic lipase deacylation was used to study the variation in distribution of the fatty acids at the sn-2-position of milk fat triglycerides of a series of butters and of the milk obtained from a cow on a restricted feeding regimen. Selected samples were analysed for stereospecific distribution of their triglyceride fatty acids which were found to be esterified in a non-random manner. The percentage of a fatty acid at the sn-3 position generally decreased with increase in the chain length of the acid, the reverse occurred at the sn-1-position. There was no major variation in the stereospecific distribution of fatty acids throughout the year, the variation that did occur was exhibited mainly by the medium chain length acids. Variation was greater at the sn-1-and sn-3-position than at the sn-2-:-position and when the proportion of an acid varied at the sn-1-position it usually varied at the sn-3-position in the reverse manner. For the milk samples it was found that change in triglyceride fatty acid composition was not associated with random increases or decreases of fatty acids at the 3 stereospecific positions. With changing total triglyceride fatty acid composition (6:0, 8:0, 10:0, 12:0, 14:0, and 16:0 decreasing and 18:0, and 18:1 increasing) the percentage of 6:0, 8:0, 10:0, 12:0, 14:0, and 16:0 acids at the sn-3-position decreased while the percentage of 18:0 and 18: 1 acids increased. These changes were compensated for by changes in the opposite direction at the sn-1- and sn-2- positions. The 1,2,3-random, l,3-ra.ndom-2-random and l-random-2-random-3- random fatty acid distribution hypotheses were evaluated using the data from the stereospecific analyses of butters. The l-random-2-random-3-random hypothesis provided the best agreement between calculated and observed triglyceride species composition. No relationship was found between the trisaturated glyceride content of milk fat and softening point. Interesterification of milk fat which increased the softening point and randomly distributed the fatty acids at the 3 stereospecific positions also produced increased amounts of high melting point triglycerides. Triglyceride species composition of the trisaturated glyceride fraction of butters was found to vary seasonly. Excellent correlation was found between softening point and groups of low molecular weight triglycerides, groups of high molecular weight triglycerides aid some individual triglyceride species. Correlation coefficients were higher than those previously reported between groups of fatty acids and softening point