Identification of Enriched Conjugated Linoleic Acid Isomers in Cultures of Ruminal Microorganisms after Dosing with 1-13C-Linoleic Acid

Most studies of linoleic acid biohydrogenation propose that it converts to stearic acid through the production of cis-9 trans-11 CLA and trans-11 C18:1. However, several other CLA have been identified in ruminal contents, suggesting additional pathways may exist. To explore this possibility, this research investigated the linoleic acid biohydrogenation pathway to identify CLA isomers in cultures of ruminal microorganisms after dosing with a C-13 stable isotope. The C-13 enrichment was calculated as [(M+1/M)x100] in labeled minus unlabeled cultures. After 48 h incubation, significant C-13 enrichment was observed in seven CLA isomers, indicating their formation from linoleic acid. All enriched CLA isomers had double bonds in either the 9,11 or 10,12 position except for trans-9 cis-11 CLA. The cis-9 trans-11 CLA exhibited the highest enrich ment (30.65%), followed by enrichments from 21.06 to 23.08% for trans-10 cis-12, cis-10 trans-12, trans-9 trans-11, and trans-10 trans-12 CLA. The remaining two CLA (cis-9 cis-11 and cis-10 cis-12 CLA) exhibited enrichments of 18.38 and 19.29%, respectively. The results of this study verified the formation of cis-9 trans-11 and trans-10 cis-12 CLA isomers from linoleic acid biohydrogenation. An additional five CLA isomers also contained carbons originating from linoleic acid, indicating that pathways of linoleic acid biohydrogenation are more complex than previously described.