Rapid analysis of the isomers of trans-octadecenoic acid in milk fat

Contents of total trans-octadecenoic acid and of 13 positional isomers between trans-Delta 4 and trans-Delta 16 were determined on 1756 German and a further 111 milk fat samples from 10 other EU countries. Argentation thin-layer chromatography (Ag-TLC) combined with gas-liquid chromatography (GLC) was used to develop a rapid method based on triglyceride combinations for the determination of all positional isomers of trans-octadecenoic acid. Triglyceride formulae were derived statistically from both triglyceride and trans fatty acid data for 100 milk fat samples. The formula for total trans-C18:1 contents exhibited a standard Error of estimation (see) = 0.293% and a correlation coefficient r = 0.998. Determination of total trans-C18:1 contents with high precision (see = 0.065%, r = 0.99988) was accomplished by correlating data from direct FAME-GLC on a 100 In column of high polarity. A mean trans-octadecenoic acid content of 3.62 wt% of total fatty, acids was found for milk fat; the mean proportions of isomers trans-Delta 4, trans-Delta 5, trans-Delta 6-8, trans-Delta 9, trans-Delta 10, trans-all, trans-Delta 12, trans-Delta 13/14, trans-Delta 15 and trans-Delta 16 were 0.05, 0.05, 0.16, 0.23, 0.17, 1.72, 0.21, 0.49, 0.28 and 0.33 wt% respectively. Copyright (C) 1996 Elsevier Science Limited