Abstract
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 13C stable isotope. The 13C enrichment was calculated as [(M+1/M)×100] in labeled
minus unlabeled cultures. After 48 h incubation, significant 13C 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 enrichment
(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.
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