OPTIMIZED ANALYSIS OF TRANS-OCTADECENOIC ACIDS IN EDIBLE FATS

Trans fatty acids (TFA) in edible fats are of interest, since they are suspected to influence serum lipid levels. Thus, to estimate the atherogenic potency of edible fats a precise analytical method for the determination of TFA is required. The present study does not only aim at the quantitative analysis of total C18:1 TFA, but also at the determination of the isomeric pattern of trans-octadecenoic acids in different fats. The combination of argentation TLC with high resolution gas chromatography allows the quantification of 10 trans- and 9 cis-octadecenoic acid peaks. This method can be applied to hydrogenated vegetable fats as well as to ruminant fats and tissue lipids from different species. Based on this two-dimensional chromatography the intake of single TFA isomers with food can be determined, which is of importance with respect to the hypothesis, that the negative metabolic activity originates only from certain isomers, and to the considerable variation of isomeric patterns in different edible fats. Based on the precise determination of the total trans-octadecenoic acid content in milk fats by TLC and GC, a formula has been derived by regression analysis, which allows the evaluation of total C18:1 TFA contents from a routine GC analysis. Though the 61 milk fats used covered a wide scope of feeding and lactation conditions, a correlation coefficient of 0.9991 was achieved.