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Triglyceride Structure of Cows' Milk Fat. I. Preliminary Observations on the Fatty Acid Composition of Positions 1, 2, and 3^{1, 2,}

Department of Animal Industries, University of Connecticut, Storrs

ABSTRACT

Pancreatic lipolysis has proven to be extremely useful in the determination of milk fat triglyceride (TG) structure; however, with pancreatic lipase alone, the separate compositions of positions 1- and 3- cannot be determined. A positional analysis can be accomplished by the method of Brookerhoff (3), in which the 1,2- and 2,3-diglycerides (DG's) from a pancreatic lipolysis of fat are converted to phosphatidyl phenols. These are then digested with phospholipase A, which is specific for the 3 (L) phosphatidyl phenol, releasing the 2-(ß) acid, and forming a lysophosphatide containing an acid in the 1-position. Subsequent analysis of the fatty acids in the various fractions allows determination of the 1- and 3-positions separately. With this procedure, it is possible to ascertain whether the fatty acids of milk fat are randomly distributed between the 1- and 3- positions or if mixtures of single enantiomers exist. The latter was predicted (7) from Patton and McCarthy's hypothesis (9), that most butyryl TG's are formed by the esterification of butyric acid (4:0) to , ß-DG's.

¹ Scientific contribution no. 262, Agricultural Experiment Station, University of Connecticut, Storrs. Supported in part by Public Health Service Research Grant AM-02605-09 from the Institute of Arthritis and Metabolic Diseases.

² Numbering of positions is according to the system of Hirschmann (6) where, for example, L--phosphatidyl choline becomes 3-phosphatidyl choline.