Gamma-Nonalactone in Beer: Biosynthesis by Yeast

Abstract

Gamma-Nonalactone is known as an aroma active and chiral compound in beer and other fermented products. Labeling experiments with tetra deuterated (9,10,12,13-²H₄)-linoleic acid, single deuterated 13- and 9- hydroxyoctadecadienoic acids (HODE) and its corresponding oxygen-18 labeled oxidation product [¹⁸O₁]- 13- and 9- HODE elucidated two different biosynthetic routes from linoleic oxidation products (HODE) to gamma-nonalactone in brewers yeast Saccharomyces cerevisiae and a model yeast Sporobolomyces odorus.

I)13-Peroxidation of linoleic acid into 13-HODE in barley or during malting and beta-oxidation followed by one alpha-oxidation type step finally resulting in gamma-nonalactone with (S)-stereospecificity ( (S) ~ 60 % e.e.).

II)9-Peroxidation of linoleic acid into 9-HODE in barley or during malting and Baeyer-Villiger type oxidation resulting in 2E,4E-nonadien-1-ol and azelaic acid. 2E,4E-nonadien-1-ol was further transformed to gamma-nonalactone with (R)-stereo-specificity( (R) ~ 46 % e.e.).