Biohydrogenation of Linolenic Acid to Stearic Acid by the Rumen Microbial Population Yields Multiple Intermediate Conjugated Diene Isomers

Abstract

AbstractThe current literature suggests that linolenic acid biohydrogenation converts to stearic acid without the formation of CLA. However, a multitude of CLA were identified in the rumen that are generally attributed to linoleic acid biohydrogenation. This study used a stable isotope tracer to investigate the biohydrogenation intermediates of 13C-linolenic acid, including CLA. A continuous culture fermenter was used to maintain a mixed microbial population obtained from the rumen of cattle at pH 6.5 for 6 d. The mixed fermenter contents were then transferred to batch cultures containing either 13C-labeled or unlabeled linolenic acid, which were run in triplicate for 0, 3, 24, and 48 h. The 13C enrichment was determined by GC-MS. After 48 h of incubation, 8 CLA isomers were significantly enriched, suggesting that these CLA isomers originated directly from linolenic acid. The cis-10, cis-12 CLA isomer exhibited the highest enrichment (21.7%), followed by cis-9, cis-11 and trans-8, trans-10 CLA. The enrichment of these 2 CLA isomers ranged from 20.1 to 21.1% and the remaining 5 CLA including cis-9, trans-11 CLA were ,15.0%. A multitude of nonconjugated and partially conjugated 18:2 and 18:3 isomers was enriched during the 48 h of incubation. The results of this study confirm that mixed ruminal microbes are capable ofthe formation of several CLA and 18:3 isomers from linolenic acid, indicating that linolenic acid biohydrogenation pathwaysare more complex than previously reported.