STUDIES ON SOME FACTORS RESPOSIBLE FOR CONJUGATED LINOLEIC ACID CONTENT IN FOODS OF RUMINANT ORIGINS

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Conjugated linoleic acid (CLA) is a collective term used to describe one or more positional and geometric isomers of linoleic acid. Of the CLA isomers, cis9, trans11 isomer which is found primarily in ruminants amounts as much as 80〜90% of the total CLA content of foods of ruminant origins. The cis9, trans11 isomer of CLA has been shown in animals to have an anticarcinogenic property. It is believed that cis9, trans11 CLA isomer is produced in the rumen as intermediates in the biohydrogenation of dietary linoleic acid to stearic acid. Our works have demonstrated that the cis9, trans11 CLA contents of meat and fat from ruminants fed a relatively high roughage ration is significantly higher than those from ruminants fed a relatively high concentrate ration, with the results suggesting that α -linolenic acid present predominantly in pasture lipid might be involved in the formation of cis9, trans11 CLA.Therefore, crashed corn high in linoleic acid and Italian ryegrass hay high in α -linolenic acid were incubated with rumen liquor culture. The yield of cis9, trans11 CLA from the Italian ryegrass was siginificantly higher than that from the crashed corn. This findings suggested the formation of cis9, trans11 CLA via α -linolenic acid. α -Linolenate was incubated with rumen liquor culture. The formation of cis9, trans 11 CLA from α -linolenate was first observed in the rumen liquor culture, and the pH value of the rumen liquor culture also influenced the metabolism. The results showed that α -linolenate incubated with rumen liquor culture produced three intermediate metabolites of which c9, t11, c15 octadecatrienoic acid might be involved in the formation of cis9, trans11 CLA in the rumen. The results obtained in the present study confirmed for the first time that in additoin to linoleic acid, α -linolenic acid present predominantly in pasture lipid may serve as a potential precursor of cis9, trans 11 CLA in the rumen.