A new type of flavor precursors in Vitis vinifera L cv Sauvignon blanc:: S-cysteine conjugates

Three flavor-active volatile thiols (4-mercapto-4-methylpentan-2-one, 4-mercapto-4-methylpentan-2-ol and 3-mercaptohexan-1-ol) involved in Vitis vinifera L. var. Sauvignon blanc wine aroma can be generated in vitro from nonvolatile must extracts by the enzyme action of a cell-free extract obtained from the gastrointestinal bacterium Eubacterium limosum. The specificity of a cysteine conjugate beta-lyase (EC 4.4.1.13) which is contained in the cell-free extract, strongly suggested the existence of precursor for these volatile thiols having a structure of S-cysteine conjugate. Gasphase chromatography analysis coupled with mass spectrometry of must extract in the form of trimethylsilylated derivatives, verified this hypothesis. The release of flavor-active volatile thiols during alcoholic fermentation of the must is shown to be due to the degradation, by yeast, of the corresponding S-cysteine conjugates. This mechanism explains the amplification of the typical Sauvignon blanc grape aroma during alcoholic fermentation.