POSTPARTURITION CHANGES IN THE TRIACYLGLYCEROLS OF COW COLOSTRUM

The changes in the triacylglycerol (TAG) composition of colostrum fat of three cows were studied. In addition to the determination of fatty acid composition by gas chromatography, the distribution of TAG accord ing to the acyl carbon number (ACN) and molecular weight was analyzed utilizing both supercritical fluid chromatography (SFC) and ammonia ne gative-ion chemical ionization mass spectrometry (MS). Colostrum TAG c ontained substantially less stearic and oleic acids and more myristic and palmitic acids than the normal Finnish milk fat. The major trends in the changes of fatty acids and TAG were similar for each cow, altho ugh clear differences between individuals were found. During the first week of parturition, the proportions of short-chain fatty acids (C-4- C-10) typically increased as well as those of stearic and oleic acids, whereas the relative amounts of C-12-C-16 acids decreased, especially those of myristic and palmitic acids. Distinct changes occurred also in TAG distributions: the proportions of molecules with ACN 38-40 incr eased and those with ACN 44-48 decreased. Although there were distinct differences between individuals shortly after delivery, both the fatt y acid compositions and TAG distributions of the milk samples of the c ows started to resemble each other after one week. The theoretical pro files of colostrum TAG calculated based on the fatty acid compositions differed clearly from the ACN distributions analyzed by SFC and MS. T hus, the analysis of TAG is essential, because the changes in molecula r species composition of colostrum TAG cannot be estimated according t o the fatty acid analysis alone.