title: Unexpected Formation of Low Amounts of (R)-Configurated anteiso-Fatty Acids in Rumen Fluid Experiments.
abstract: Anteiso-fatty acids (aFA) with odd carbon number are a class of branched-chain fatty acids (BCFA) mainly produced by bacteria. Bacterial sources are also made responsible for their occurrence in the low percent-range in lipids of ruminants (meat and milk) and fish. aFAs are chiral molecules and typically occur predominantly in form of (S)-enantiomers, and their primary precursor has been noted to be isoleucine. Yet, low proportions of (R)-aFAs were also detected in fish and cheese samples. Here we investigated the potential formation of (R)-aFAs by means of incubation experiments with rumen fluid from fistulated cows. Supplementation of rumen fluid with both L- and DL-isoleucine, resulted in a significant (α <0.05) increase of the aFA concentrations but in both cases enantiopure (S)-aFAs were observed. By contrast, incubations without addition of any isoleucine lead to a significant (α <0.05) formation of small proportions of (R)-aFAs similarly to those previously observed in fish and cheese. These results were consistently reproduced in three different years with rumen fluid from different cows fed different diets. All findings point to the existence of a further biosynthesis pathway of aFAs with different stereospecificity than the classic one using isoleucine as primer.
authors.affiliation: University of Hohenheim, Institute of Food Chemistry (170b), Stuttgart, Germany.
authors.forename: Dorothee
authors.identifier: http://orcid.org/0000-0001-6838-8206
authors.initials: D
authors.lastname: Eibler
authors.affiliation: University of Hohenheim, Institute of Food Chemistry (170b), Stuttgart, Germany.
authors.forename: Halima
authors.initials: H
authors.lastname: Abdurahman
authors.affiliation: University of Hohenheim, Institute of Food Chemistry (170b), Stuttgart, Germany.
authors.forename: Tanja
authors.initials: T
authors.lastname: Ruoff
authors.affiliation: University of Hohenheim, Institute of Food Chemistry (170b), Stuttgart, Germany.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Kaffarnik
authors.affiliation: University of Hohenheim, Institute of Animal Science (460a), Stuttgart, Germany.
authors.forename: Herbert
authors.initials: H
authors.lastname: Steingass
authors.affiliation: University of Hohenheim, Institute of Food Chemistry (170b), Stuttgart, Germany.
authors.forename: Walter
authors.initials: W
authors.lastname: Vetter
mesh_terms: D000818:Animals; D001826:Body Fluids / Q000737:chemistry / Q000378:metabolism; D002244:Carbon / Q000737:chemistry; D002417:Cattle; D002611:Cheese; D005227:Fatty Acids / Q000737:chemistry* / Q000378:metabolism; D007532:Isoleucine / Q000737:chemistry / Q000494:pharmacology; D007774:Lactation; D008055:Lipids / Q000737:chemistry*; D008892:Milk / Q000737:chemistry; D012417:Rumen / Q000737:chemistry* / Q000378:metabolism
chemical_list: D005227:Fatty Acids; D008055:Lipids; D007532:Isoleucine; D002244:Carbon