Stereospecificity of 10-Hydroxystearic Acid and Formation of 10-Ketostearic Acid by Lactic Acid Bacteria

Abstract

We studied the variation in enantiomeric excess of 10-hydroxystearic acid (10-HSA) produced by several strains of lactic acid bacteria from oleic acid. Using 1H-nuclear magnetic resonance and chiral-phase HPLC to reveal the microorganisms involved and the mechanisms of the formation, we found that most strains produced nearly optically pure (R)-10-HSA. Among them, one strain of Lactobacillus hilgardii, isolated from a distillery in Scotland, produced 10-HSA with lower enantiomeric excess, and furthermore, the strain produced a large amount of 10-ketostearic acid along with the 10-HSA. In this strain, 10-ketostearic acid was found to be generated from 10-HSA supplied to the cells. Also, the enantiomeric excess of γ-dodecalactone, formed from 10-ketostearic acid by distiller's yeasts, was found to be within the range of −17 to 32%; these findings were consistent with the distribution of the enantiomers in malt whiskies. From these results, two conceivable pathways for the formation of lactones during the production of malt whisky were proposed: from 10-ketostearic acid with the involvement of distiller's yeast and from nondistiller's yeast with 10-HSA as an intermediate.