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Interpretation of Pancreatic Lipase Analyses of Cow's Milk Fat Triglyceride Structure¹

Department of Animal Industries, University of Connecticut, Storrs

ABSTRACT

Initially, cow's milk fat was digested at various temperatures with two levels of pancreatic lipase, but this was unsuccessful in eliminating intermolecular specificity. Next, the fatty acid compositions of the monoglycerides (MG) from similar digestions were determined by gas-liquid chromatography as methyl and butyl esters. These were found to vary with the extent of hydrolysis, the short-chain fatty acids being present in lesser proportions in the MG after extensive hydrolysis. The differing compositions were attributed to preferential digestion of certain triglyceride (TG) species and to the nonrandom distribution of fatty acids in the 2 position among TG classes. Subsequently, this was confirmed when residual TG from a milk fat-pancreatic lipase digestion were submitted to a second digestion and the resulting MG compared to those obtained in the initial lipolysis.

During these studies, the presence of butyric acid (4:0) in the 2 position of milk fat TG was also observed. Therefore, possible preferential acyl migration of 2-position 4:0 was investigated by analysis of the free fatty acids (FFA) and MG resulting from digestion of a mixture of synthetic glyceryl-2-butyrate -1,3- dipalmitate and triolein. As indicated by some 2-position 4:0 observed in the FFA, migration possibly occurred, but evidence for preferential migration was inconclusive.It is concluded that for intact cow's milk fat triglycerides, quantitative calculations of the 1,3-random, 2-random type are not valid.

¹ Scientific contribution no. 152, Agricultural Experiment Station, University of Connecticut, Storrs. Supported in part by Public Health Service research grant AM-02605-07 from the Institute of Arthritis and Metabolic Diseases.

² Present address: Department of Food Science and Technology, Oregon State University, Corvallis, Oregon.