trans Fatty acids in milkfat

Milkfat is extremely complex, with ca. 500 different fatty acids reported in the triglycerides. Seasonal feed variation results in higher unsaturated fatty acid levels in summer than in winter. Rumen microbes hydrogenate unsaturated feed lipids to yield a mixture of geometrical and positional isomers which are transmitted to the milk. Total isolated trans fatty acids in milkfat reported in the literature range from 2 to 11% with maximal values in summer and minimal values in winter. A study was undertaken about the use of AOCS Method Cd 14‐61 for the determination of isolated trans levels in milkfat. The triglycerides of milkfat were analyzed using trielaidin as a standard and milkfat methyl esters were analyzed using methyl elaidate as a standard. Corrections were made, for the loss of the methyl esters of the short‐chain fatty acids. The apparent levels of trans found by using the triglycerides were considerably higher than by using the methyl esters. Infrared spectra of pure triglycerides of saturated fatty acids showed measurable absorption at 10.36 μm, whereas methyl esters of saturated and cis unsaturated fatty acids did not.