Quantitative analysis of long-chain trans-monoenes originating from hydrogenated marine oil

Gas chromatography (GC) is used for the analysis of trans-fatty acids in pa rtially hydrogenated vegetable oils. Although trans-isomers of C-18 carbon length predominate in partially hydrogenated vegetable oils, trans-isomers of C-20 and C-22 carbon length occur in partially hydrogenated fish oil. We report a simple silver ion chromatographic combined with capillary CC tech nique for quantitative analysis of trans-monoenes derived from partially hy drogenated fish oil. Silver nitrate thin-layer chromatographic (TLC) plates are developed in toluene/hexane (50:50, vol/vol). Fatty acid methyl esters are separated into saturates (R-f 0.79), trans-monoenes (R-f 0.4), cis-mon oenes (R-f 0.27), dienes (R-f 0.10), and polyunsaturated fatty acids with t hree or more double bonds remaining at the origin. The isolated trans-monoe nes are quantitatively analyzed by capillary GC-The technique of argentatio n TLC with GC analysis of isolated methyl esters is highly reproducible wit h 4.8% variation (i.e., coefficient of variation, CV%) in R-f values and 4. 3 and 6.9% CV% in quantification within batch and between batch, respective ly. Furthermore, the combined technique revealed that direct GC analysis un derestimated the trans-content of margarines by at least 30%. In this study , C-20 and C-22 trans-monoenes were found in relatively large quantities; 1 3.9% (range 10.3-19.6%) and 7.5% (range 5.3-11.5%), respectively, in margar ine purchased in 1995, but these C-20 and C-22 trans-monoenes were much red uced (0.1%) in a fresh selection of margarine purchased in 1998. Compositio nal data from labels underestimated the trans-content of margarines, especi ally those derived from hydrogenated marine oil. Low levels of C-20 trans-m onoenes (range 0.1-0.3%) and C-22 trans-monoenes (range 0.0-0.1%) were iden tified in adipose tissue obtained from healthy volunteers in 1995, presumab ly indicating consumption of partially hydrogenated fish oil.