, Volume 35, Issue 6, pp 681-687

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

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Abstract

Gas chromatography (GC) is used for the analysis of trans-fatty acids in partially hydrogenated vegetable oils. Although trans-isomers of C18 carbon length predominate in partially hydrogenated vegetable oils, trans-isomers of C20 and C22 carbon length occur in partially hydrogenated fish oil. We report a simple silver ion chromatographic combined with capillary GC technique for quantitative analysis of trans-monoenes derived from partially hydrogenated fish oil. Silver nitrate thinlayer 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 0.49), cis-monoenes (R f, 0.27), dienes (R f, 0.10), and polyunsaturated fatty acids with three or more double bonds remaining at the origin. The isolated trans-monoenes are quantitatively analyzed by capillary GC. The technique of argentation TLC with GC analysis of isolated methyl esters is highly reproducible with 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, respectively. Furthermore, the combined technique revealed that direct GC analysis underestimated the trans-content of margarines by at least 30%. In this study, C20 and C22 trans-monoenes were found in relatively large quantities; 13.9% (range 10.3–19.6%) and 7.5% (range 5.3–11.5%), respectively, in margarine purchased in 1995, but these C20 and C22 trans-monoenes were much reduced (0.1%) in a fresh selection of margarine purchased in 1998. Compositional data from labels underestimated the trans-content of margarines, especially those dervied from hydrogenated marine oil. Low levels of C20 trans-monoenes (range 0.1–0.3%) and C22 trans-monoenes (range 0.0–0.1%) were identified in adipose tissue obtained from healthy volunteers in 1995, presumably indicating consumption of partially hydrogenated fish oil.