Metabolism of conjugated linoleic acids and 18 : 1 fatty acids by ruminal bacteria: products and mechanisms

Abstract

Cultures of ruminal bacteria known to metabolize unsaturated fatty acids were grown in medium containing 50 mg ml "1 of geometric and positional isomers of conjugated linoleic acid (CLA) or 18 : 1 fatty acids and 37.4 % deuterium oxide to investigate the mechanisms responsible for fatty acid metabolism. Butyrivibrio fibrisolvens JW11 converted cis-9,trans-11-18 : 2 and trans-9,trans-11-18 : 2 to trans-11-18 : 1 as the main product, labelled at C-9, and metabolized trans-10,cis-12-18 : 2 to trans-10-18 : 1, labelled at C-13, and smaller amounts of trans-12-18 : 1 and cis-12-18 : 1. Butyrivibrio proteoclasticus P-18 did not grow in the presence of cis-9,trans-11-18 : 2 or trans-10,cis-12-18 : 2, but grew in medium containing trans-9,trans-11-18 : 2, forming 18 : 0. Propionibacterium acnes, a ruminal species that isomerizes linoleic acid to trans-10,cis-12-18 : 2, did not metabolize CLA isomers further. B. fibrisolvens metabolized small amounts of trans-10-18 : 1, trans-11-18 : 1 and cis-9-18 : 1, but the products formed were not detected. B. proteoclasticus, on the other hand, carried out substantial conversion of 18 : 1 substrates to 18 : 0. P. acnes hydrated cis-9-18 : 1 and trans-11-18 : 1 to 10-OH-18 : 0, which was further oxidized to yield 10-O-18 : 0. The deuterium enrichment in the intermediates formed during incubations with 9,11 geometric isomers of CLA was about half that of the products from trans-10,cis-12 CLA and 18 : 1 isomers, suggesting that the reduction of 9,11 geometric isomers CLA by ruminal bacteria occurs via different mechanisms compared with the metabolism of other unsaturated fatty acids.

Animal performance and meat characteristics in steers reared in intensive conditions fed with different vegetable oils

“…Although the OLI diet provides a greater amount of c 9-18:1 than the PALM diet (Table 2), the content of this FA in the OLI meat fat did not differ from that of the PALM meat fat. These results could be explained by the abundance of 18:0 in the PALM diet, which reaches the adipose tissue and, as mentioned previously, is partly converted into c 9-18:1 via Δ9 desaturase, while the c 9-18:1 provided by the OLI diet is susceptible to isomerization in the rumen and the formation of several trans-monoenes isomers (Mosley et al, 2002;McKain et al, 2010).…”

“…In the rumen, c 9,t 11-18:2 is produced during biohydrogenation of c 9,c12-18:2n-6 (Griinari and Bauman, 1999). In vitro studies have shown that during the biohydrogenation of oleic acid, small amounts of t 11-18:1 are also produced (Mosley et al, 2002;McKain et al, 2010). The c 9,t 11-18:2 present in adipose tissue comes from ruminal biohydrogenation of c 9,c12-18:2n-6 (Griinari and Bauman, 1999) Vegetable oils and meat quality in beef and from the endogenous synthesis from t 11-18:1.…”

“…Oleic acid is susceptible to isomerization in the rumen, resulting in the formation of a variety of trans-monoene isomers (Mosley et al, 2002;McKain et al, 2010). These isomers could be transferred to milk fat or meat fat.…”

Role of trans fatty acids in the nutritional regulation of mammary lipogenesis in ruminants

“…Incubations with mixed or pure cultures of rumen bacteria demonstrated that OA can be biohydrogenated to 18:0 (Harfoot and Hazlewood, 1988), whereas more recent studies indicated that metabolism of OA in vitro results in the formation of oxygenated fatty acids (10-OH 18:0 and 10-O 18:0) and numerous trans-18:1 intermediates with double bonds at positions D6-D16 (Mosley et al, 2002;Jenkins et al, 2006;McKain et al, 2010; Figure 1). Direct comparisons indicate that the extent of biohydrogenation of OA is also lower compared with LA and LNA and typically varies between 58% and 87% (Loor et al, 2004 and2005d;.…”

“…The occurrence of numerous isomers of trans 18:1, Figure 1 Putative pathways describing cis-9 18:1 metabolism in the rumen (adapted from Mosley et al, 2002;Jenkins et al, 2006;McKain et al, 2010). Arrows with solid lines highlight the major biohydrogenation pathway, whereas arrows with dashed lines describe the formation of minor fatty acid metabolites.…”