title: High enantiomeric excess of the flavor relevant 4-alkyl-branched Fatty acids in milk fat and subcutaneous adipose tissue of sheep and goat.
abstract: Volatile 4-alkyl-branched fatty acids are characteristic flavor compounds of sheep and goat. Due to the methyl branch, the carbon C-4 represents a stereogenic center with the possible presence of one or both enantiomers in the respective samples. In this study, we used enantioselective gas chromatography to study the enantiomeric composition of 4-methyloctanoic acid (4-Me-8:0) and 4-ethyloctanoic acid (4-Et-8:0) in milk and dairy products from sheep and goat as well as in goat subcutaneous tissue. Different columns coated with modified cyclodextrins were tested to resolve racemic 4-alkyl-branched fatty acid methyl ester standards. The best enantiomer resolution was obtained on 25% octakis(2,3,6-tri-O-ethyl)-γ-cyclodextrin (γ-TECD) diluted in OV-1701. For analysis of the food samples, the lipids were extracted and fatty acids in the extracts were converted into fatty acid methyl esters. Non-aqueous reversed-phase high-performance liquid chromatography was used to fractionate the samples in order to gain one solution enriched in 4-Me-8:0 methyl ester and one solution enriched with 4-Et-8:0 methyl ester. Subsequent analysis by enantioselective gas chromatography with mass spectrometry allowed only the detection of one enantiomer of 4-Me-8:0 and 4-Et-8:0 in the samples. By means of a non-racemic standard of 4-Me-8:0, it was found that the predominant enantiomer was (R)-4-Me-8:0.
authors.affiliation: University of Hohenheim , Institute of Food Chemistry (170b), Garbenstraße 28, 70593 Stuttgart, Germany.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Kaffarnik
authors.forename: Carolina
authors.initials: C
authors.lastname: Heid
authors.forename: Yasemin
authors.initials: Y
authors.lastname: Kayademir
authors.forename: Dorothee
authors.initials: D
authors.lastname: Eibler
authors.forename: Walter
authors.initials: W
authors.lastname: Vetter
mesh_terms: D000273:Adipose Tissue / Q000737:chemistry*; D000818:Animals; D005223:Fats / Q000737:chemistry*; D005227:Fatty Acids / Q000737:chemistry*; D005421:Flavoring Agents / Q000737:chemistry*; D006041:Goats; D008892:Milk / Q000737:chemistry*; D012756:Sheep; D013237:Stereoisomerism
chemical_list: D005223:Fats; D005227:Fatty Acids; D005421:Flavoring Agents
keywords: alkyl-branched-chain fatty acids; enantioselective analysis; goat; milk; modified cyclodextrins; sheep