BOARD-INVITED REVIEW: Recent advances in biohydrogenation of unsaturated fatty acids within the rumen microbial ecosystem1

Abstract

Recent advances in chromatographic identification of CLA isomers, combined with interest in their possible properties in promoting human health (e.g., cancer prevention, decreased atherosclerosis, improved immune response) and animal performance (e.g., body composition, regulation of milk fat synthesis, milk production), has renewed interest in biohydrogenation and its regulation in the rumen. Conventional pathways of biohydrogenation traditionally ignored minor fatty acid intermediates, which led to the persistence of oversimplified pathways over the decades. Recent work is now being directed toward accounting for all possible trans-18:1 and CLA products formed, including the discovery of novel bioactive intermediates. Modern microbial genetics and molecular phylogenetic techniques for identifying and classifying microorganisms by their small-subunit rRNA gene sequences have advanced knowledge of the role and contribution of specific microbial species in the process of biohydrogenation. With new insights into the pathways of biohydrogenation now available, several attempts have been made at modeling the pathway to predict ruminal flows of unsaturated fatty acids and biohydrogenation intermediates across a range of ruminal conditions. After a brief historical account of major past accomplishments documenting biohydrogenation, this review summarizes recent advances in 4 major areas of biohydrogenation: the microorganisms involved, identification of intermediates, the biochemistry of key enzymes, and the development and testing of mathematical models to predict biohydrogenation outcomes.

Effects of ewes grazing sulla or ryegrass pasture for different daily durations on forage intake, milk production and fatty acid composition of cheese

“…The incomplete saturation of dietary PUFA into stearic acid gives origin to both VA and RA in the rumen; VA is the last intermediate of LA and ALA biohydrogenation, formed also by the isomerisation of OA, whereas RA is formed at the first step of biohydrogenation of LA (Bauman et al, 2006;Chilliard et al, 2007). However, the increase in RA in S8 cheeses has to be linked mainly to the conversion of VA flowing from the rumen into RA, occurring in the mammary gland through the activity of the Δ-9 desaturase enzyme system (Chilliard et al, 2007;Jenkins et al, 2008), and favoured by a high level of VA (Bauman et al, 2006).…”

Metabolic diversity in biohydrogenation of polyunsaturated fatty acids by lactic acid bacteria involving conjugated fatty acid production

“…The main aim of investigations on ruminal PUFA-biohydrogenation is to create healthier ruminant products with low saturated fatty acid and high n-3 fatty acid contents (Scollan et al 2001;Jenkins et al 2008), and with potentially health-promoting CLA, mainly cis-9,trans-11-CLA. Considerable progress has been made in tracing intermediates of linoleic acid biohydrogenation.…”

“…Conjugated 18:3 is regarded as an intermediate of PUFA-biohydrogenation occurring in the rumen, which affects the fatty acid compositions of dairy products. Understanding of the PUFA-biohydrogenation process in the rumen is important for improving the fatty acid profiles of diary products so as to be rich in n-3 polyunsaturated fatty acids and CLA (Scollan et al 2001;Jenkins et al 2008). With respect to this, α-linolenic acid transformation by rumen bacteria was investigated and it was found that cis-9, trans-11,cis-15-18:3 is an initial intermediate, which is further transformed into trans-11,cis-15-octadecadienoic acid (18:2) and then to trans-11-octadecenoic acid (18:1).…”

Milk fat depression and energy balance in stall-fed dairy goats supplemented with increasing doses of conjugated linoleic acid methyl esters

“…In addition, a rumen biohydrogenation of 95% for CLA-ME was assumed to occur (Jenkins et al, 2008). The nutrient requirements were calculated according to the National Research Council (NRC) (2007) and the diet formulations were carried out using the Small Ruminant Nutrition System (Tedeschi et al, 2010).…”