Isomeric distribution and rapid determination of trans-octadecenoic acids in German brands of partially hydrogenated edible fats

The determination of trans fatty acids (TFA), in particular trans-octadecenoic acids, in edible fats is of current interest, since just in the last years a variety of negative physiological effects has been related to TFA. A main source of C18:1 trans fatty acids are partially hydrogenated fats. Besides the total content of trans-octadecenoic acids, their isomeric distribution seems to be even more important, as fats of different origin, e.g, partially hydrogenated fats and ruminant fats, possibly show different physiological properties. In this study, 46 margarines and 16 shortenings and cooking fats, purchased in August of 1994, were analyzed for trans-octadecenoic acid isomers by a two-step method (Ag-TLC/HRGC). The mean relative isomeric distributions (g/100 g TFA) of both groups determined with a 100 m-column were comparable, with Delta 9 and Delta 10 being the main isomers. By repeated analysis of 15 brands between August of 1994 and January of 1996, the mean total C18:1 TFA content was found to have decreased in these margarines (n=8) from 9.58% to 4.62% but not in shortenings/cooking fats (n=7; 11.62% to 11.92%). The relative isomeric distribution was not affected in both groups. To avoid the problem of overlaps between cis- and trans-C18:1 isomers with GC analysis, formulae for the rapid determination of total C18:1 TFA contents in margarines and shortenings/cooking fats from direct GC data were statistically derived. Thus, applying these formulae and considering the mean relative distributions, absolute contents of ail individual isomers of trans-octadecenoic acids can rapidly be deter mined from direct GC.