In vitro biohydrogenation of n − 3 polyunsaturated fatty acids protected against ruminal microbial metabolism

The objective of this study was to investigate, in vitro, methods of protecting n − 3 polyunsaturated fatty acids from biohydrogenation in the rumen. Linseed oil (LO) was used as a source rich in α-linolenic acid (18:3n − 3), and was compared with whole linseed (LS), formaldehyde-treated linseed (FL), formaldehyde-treated linseed that was pre-treated with sodium hydroxide (SFL), formic acid (FFL) or ammonium tetraformate (AFL), xylose treated linseed (XL) or linseed oil absorbed into a fibre source (ALO). Fish oil (FO) was used as an oil rich in eicosapentaenoic acid (20:5n − 3) and docosahexaneoic acid (22:6n − 3), and was compared with fish oil encapsulated with saturated fat (EFa and EFb), marine algae (AG) or fish oil absorbed into a fibre source (AFO). In addition, there was a control (C) with no added oil. The oil sources were incubated using a batch culture technique, and the fermentation terminated after 6, 12, 24 and 48 h. Gas production profiles were similar for the treatments high in 18:3n − 3, whilst the potential extent of gas production was lower (P < 0.01) in FO compared with C, EFa, EFb, AG or AFO. For treatments high in 18:3n − 3, vessel fluid pH decreased (P < 0.001) with time, and was highest (P < 0.001) in C, but did not differ among treatments. Vessel pH also decreased (P < 0.001) with time in treatments high in 20:5n − 3and 22:6n − 3, and was highest (P < 0.001) in C and FO. Biohydrogenation of 18:3n − 3 was extensive in treatments LO, LS, FL, AFL, XL and ALO, with mean values at 48 h of incubation of 966, 974, 919, 897, 874 and 904 g/kg respectively, and was lower (P < 0.001) in SFL and FFL (values at 48 h of 557 and 693 g/kg, respectively). The major biohydrogenation intermediary product in treatments high in 18:3n − 3 was trans 18:1, which was highest at 48 h in treatments LO and LS (P < 0.001). Biohydrogenation of 20:5n − 3, but not 22:6n − 3, increased with time (P < 0.01), and was lowest in AG (P < 0.01). Pre-treatment of linseed using sodium hydroxide or formic acid, followed by formaldehyde treatment, offers the best protection against ruminal microbial biohydrogenation, whilst the degree of biohydrogenation of 22:6n − 3 in marine algae was particularly low.