The hydrogenation of some cis- and trans-octadecenoic acids to stearic acid by a rumen Fusocillus sp.

The hydrogenation of a range of double-bond positional and configurational octadecenoic acid isomers (cis (delta 2 and delta 4 to delta 13) and trans (delta 2 and delta 5 to delta 13] to stearic acid by a rumen Fusocillus sp. were examined. The cis and trans delta 5 to delta 13 isomers were all hydrogenated to some extent by late-log-phase cultures added to suspensions of individual isomers and incubated for a further 3 h. Of the cis-isomers, delta 5 to delta 11 (79-73% conversion to stearic acid) were the preferred substrates. delta 12-cis- (30%) and delta 13-cis-isomers (5%) were poorly hydrogenated. Of the trans-isomers, delta 8, delta 9 and delta 10 were 45% converted to stearic acid, the other isomers were poorly hydrogenated. These results are in agreement with less extensive studies using sheep rumen micro-organisms. When cultures were grown from small inocula in media containing individual isomers more extensive hydrogenation was found than with late-log-phase cultures. At 24 h, cis delta 2, delta 4 and delta 5 gave the highest conversions to stearic acid (90%) followed by the cis delta 6 to delta 12 and trans delta 8 to delta 10 isomers (approximately 75%), although at 6 and 12 h delta 9-trans gave higher yields of stearic acid than delta 9-cis, probably because the growth of the cis cultures showed a longer log-phase.