Enantioseparation and optical rotation of flavor-relevant 4-alkyl-branched fatty acids.

Short chain 4-alkyl-branched fatty acids are character impact compounds of the flavor of sheep and goat milk and meat. Due to their methyl or ethyl branches these volatile fatty acids are chiral, and both enantiomers are characterized by different aroma intensities. Recently, it was found that 4-methyloctanoic acid (4-Me-8:0), 4-ethyloctanoic acid (4-Et-8:0), and 4-methylnonanoic acid (4-Me-9:0) are enantiopure in goat and sheep samples, if present. Here we generated enantiopure or enantioenriched standards from racemates by means of (R)-selective esterification with lipase B and verified that 4-Me-8:0, 4-Et-8:0 and 4-Me-9:0 were (R)-enantiopure in these tissues. Determination of the optical rotation and [α]