Conjugated linoleic acid of foods originated from ruminant animals and its precursor in feeds

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Conjugated linoleic acids (CLCs) are isomers of linoleic acid which have recently gained importance as one of the biologically active substances in food. Among the various CLA isomers, the 9cis,11trans CLA (9c,11t CLA) found in beef has been shown to have beneficial effects such as antimutagenic and serum cholesterol-lowering acitivities etc.. The objectives of this study are to develop a precise and reproducible method for determining 9c,11t CLA, to determine the 9c,11t CLA contents in various meats by using this developed method, to evaluate the 9c,11t CLA contents in meats from ruminants fed different feeds, to investigate the effects of heating, storage and lipid oxidation on 9c,11t CLA contents in meats, and then to elucidate wethere linolenic acid in feed lipids serves as a precursor of 9c,11t CLA or not .We have devolved a capillary gas liquid chromatographic method for determining 9c,11t CLA in meat. Meat from ruminants contained considerably more 9c,11t CLA than meat from nonruminants. Meat and fat from the high roughage ration-fed ruminants were significantly higher than those from the high concentrate ration-fed ruminants. In addition, the results suggested that the amount of linolenic acid in roughage lipids may affect the 9c,11t CLA content of meats and fats. The results also suggested that 9c, 11t CLA in meat and meat products might be highly stable against heat treatment, storage and lipid oxidation, and that its yield may be quite a small even if 9c,11t CLA should be formed during the progress of lipid peroxidation in meat and meat products. In the incubation of rumen liquor with linolenate. The latter is isomerized to 9c,11t,15c octadecatrienoic acid. The results also suggested that 9c, 11t, CLA might be formed via a rout of hydrogenating 9c,11t,15c octadecatrienoic acid.