Triacylglycerols of winter butterfat containing configurational isomers of monoenoic fatty acyl residues. I. Disaturated monoenoic triacylglycerols

The triacylglycerols of winter butterfat were fractionated according to the type and degree of unsaturation into six fractions by silver ion high‐performance liquid chromatography (Ag‐HPLC). The acyl carbon number distribution of the triacylglycerols in each fraction was elucidated by reversed‐phase HPLC and mass spectrometry (MS). The MS analysis of each fraction gave deprotonated triacylglycerol [M ‐ H]− ions which were produced by chemical ionization with ammonia. The daughter spectrum of each of the [M ‐ H]− ions provided information on its fatty acid constituents. Successful fractionation of triacylglycerols differing in the configuration of one fatty acyl residue by Ag‐HPLC was important because geometrical isomers could not be distinguished by the MS system used. In addition to the fatty acid compositions, reversed‐phase HPLC analysis demonstrated the purity of the collected fractions: molecules having acis‐trans difference were separated nearly to the baseline. Triacylglycerols differing in the configuration of one fatty acyl residue were not equally distributed in relation to their acyl carbon numbers. This indicates that during the biosynthesis of triacylglycerols,cis‐ andtrans‐fatty acids are processed differently. Although the fatty acid compositions of the corresponding molecular weight species of disaturatedtrans‐ and disaturatedcis‐monoenoic triacylglycerols were similar, there may be differences in the amounts of different fatty acid combinations or in the distribution of fatty acids between the primary and secondary glycerol positions. In addition to the main components, it was possible to analyze minor triacylglycerols, such as molecules containing one odd‐chain fatty acid, by the MS system used.