Conversion of Unsaturated Fatty Acids to Precursors of γ-Lactones by Lactic Acid Bacteria during the Production of Malt Whisky

Abstract

We have previously reported that γ-decalactone and γ-dodecalactone contribute to the sweet and fatty flavor and quality of malt whisky. The mechanism by which these lactones are formed in malt whisky was studied. These lactones were found to be formed via hydroxy fatty acids that were produced from unsaturated fatty acids by lactic acid bacteria. The precursors were isolated by high-performance liquid chromatography and examined by gas chromatography-mass spectrometry and Fourier transform infrared. 10-Hydroxystearic acid and 10-hydroxypalmitic acid were found to be produced from oleic acid and palmitoleic acid, respectively, and these were then converted to γ-decalactone and γ-dodecalactone by yeast. The hydroxy fatty acids were found in the wash in the presence of lactic acid bacteria, and larger amounts of the acids were formed in the presence of brewer's yeast as compared to distiller's yeast only. This suggests that an interaction between lactic acid bacteria and brewer's yeast contributes to the formation of flavors in malt whisky.