Isomerization of stable isotopically labeled elaidic acid to cis and trans monoenes by ruminal microbes

Abstract

A previous study showed that oleic acid was converted by mixed ruminal microbes to stearic acid and also converted to a multitude of trans octadecenoic acid isomers. This study traced the metabolism of one of these trans C18:1 isomers upon its incubation with mixed ruminal microbes. Unlabeled and labeled (18-[ 13 C] trans -9 C18:1) elaidic acid were each added to four in vitro batch cultures with three cultures inoculated with mixed ruminal bacteria and one uninoculated culture. Samples were taken at 0, 12, 24, and 48 h and analyzed for 13 C enrichment in component fatty acids by gas chromatography-mass spectrometry. At 0 h of incubation, enrichment was detected only in elaidic acid. By 48 h of incubation, 13 C enrichment was 18% ( P Ͻ 0.01) for stearic acid, 7% to 30% ( P Ͻ 0.01) for all trans C18:1 isomers having double bonds between carbons six through 16, and 5% to 10% for cis -9 and cis -11 monoenes. After 48 h, 13 C enrichment in the uninoculated cultures was only detected in the added elaidic acid. This study shows t rans fatty acids exposed to active ruminal cultures are converted to stearic acid but also undergo enzymic isomerization yielding a multitude of positional and geometric isomers. Anaerobic bacteria that colonize the rumen, or largest of the four stomach compartments in ruminant species, carry on a process of lipid biohydrogenation whereby double bonds in unsaturated fatty acids are partially or completely eliminated. Linoleic acid disappeared completely by 50 h when incubated with mixed ruminal microorganisms (1). As linoleic acid disappeared, transient increases in a number of trans diene isomers were seen, followed by the accumulation of trans -11 C18:1. During the later hours of incubation, the trans -11 C18:1 declined slowly and was accompanied by an increase in stearic acid concentration (1).Oleic acid biohydrogenation is generally presented as a direct conversion to stearic acid without the formation of trans intermediates (1, 2). When 13 C-labeled oleic acid was incubated with ruminal microorganisms in a recent study (3), enrichment was observed not only in stearic acid but also in all trans C18:1 isomers having double bonds at carbon positions six through 16. However, the fate of these positional isomers of trans -C18:1 is not clear. Trans -11 C18:1 is readily converted to stearic acid by select ruminal bacteria (4), but its conversion to other trans monenes has not been reported.Kemp et al. (5) incubated cis ( cis -2 and cis -4 to cis -13) and trans ( trans -2 and trans -5 to trans -13) octadecenoic acid isomers with a rumen Fusocillus species. They wanted to test the ability of Fusocillus to hydrogenate the octadecenoic acids to stearic acid. Cis -5 to cis -13 and trans -5 to trans -13 isomers were all hydrogenated to some extent by late log-phase cultures incubated for 3 h. Between 73% and 79% of cis -5 to cis -11 isomers were converted to stearic acid. However, cis -12 (30%) and cis -13 (5%) were poorly hydrogenated. Of the trans isomers, 45% of trans -8, trans -9, and tr...

Effect of replacing calcium salts of palm oil distillate with incremental amounts of conventional or high oleic acid milled rapeseed on milk fatty acid composition in cows fed maize silage-based diets

“…In particular, around 70% to 100% of trans-7, trans-9, trans-10 and trans-12 18:1 were thought to originate from the isomerisation of cis-9 18:1 . Furthermore, trans-9 18:1 can be further isomerised during incubations with mixed rumen bacteria to yield a range of positional trans 18:1 isomers (Proell et al, 2002). Supplying higher amounts of cis-9 18:1 in the diet in the form of the HOR supplement in this study resulted in a higher enrichment of trans-4, trans-5 and trans-6-8 18:1 in milk fat, and a numerical but non-significant (P 5 0.09) enrichment of milk trans-9 18:1 content compared with the COR diet.…”

Effect of grain type and processing method on rumen fermentation and milk rumenic acid production

“…However, the P. acnes bacteria were cultured at pH 6.5 (Hobson, 1969), and it is not known whether they would produce t10-18:1 during the feeding of high concentrate diets. In vitro studies with mixed gut microbes reported occurrence of all possible t-18:1 isomers Proell et al, 2002), but no details were provided in their study as to which bacteria are responsible, or how a unique trans-18:1 isomer profile can be produced and maintained under specific dietary conditions.…”

Effect of fish oil on ruminal biohydrogenation of C18 unsaturated fatty acids in steers fed grass or red clover silages

“…A low apparent biohydrogenation of cis-9 C18:1 is a common feature of sole forage diets Scollan et al, 2003). This can be attributed to a partial isomerisation of other C18:1 isomers to cis-9 C18:1 (Proell et al, 2002), an endogenous contribution to cis-9 C18:1 flow at the duodenum and microbial de novo fatty acid synthesis (Merry and MacAllan, 1983). Fatty acid concentrations and content of rumen bacteria is diet dependent, with higher amounts of cis-9 C18:1 being reported on highforage diets (Bas et al, 2003).…”