Three new flavour‐active mercapto‐alcohols have been identified in Sauvignon blanc wines: 4‐mercapto‐4‐methylpentan‐2‐ol, 3‐mercaptohexan‐1‐ol and 3‐mercapto‐3‐methylbutan‐1‐ol. The first two have a perception threshold of the order of 60 ng/l in an aqueous alcohol solution and their respective odours are reminiscent of citrus zest and grapefruit. The perception threshold of 3‐mercapto‐3‐methylbutan‐1‐ol, with its odour of cooked leeks, is higher (1500 ng/l in the same solution). These three compounds may contribute towards the typical aroma of Sauvignon blanc wines. © 1998 John Wiley & Sons, Ltd.

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 β-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. Gas-phase 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. Keywords: Cysteine conjugate β-lyase; Eubacterium limosum; flavor precursor; metal ion chelated column; Sauvignon blanc; S-cysteine conjugate; varietal aroma

p-Hydroxymercuribenzoic acid (pHMB), reacts reversibly with thiols. Using this principle, an extraction method of the thiols present in wines has been established. Injecting the extracts from Vitis viniferu L. var. Sauvignon wines on to a gas-chromatographic column using the purge and trap technique and a flame photometric detector enabled us to discover some sulphur compounds present in wines from this cultivar. On several capillary columns of different polarities, one of the peaks possesses the same retention time as the potent odourant, 4-mercapto-4-methylpentan-2-one, which evokes odours of box tree and cat urine. The identification of this compound in Sauvignon wines was confirmed by mass spectrometry. These results confirm previous work obtained by coupling gas chromatography and olfactometry, and show that this thiol is present in Sauvignon wines. The perception threshold of this compound in water and in wine is very low (close to 0.1 ng/l and 3 ng/l respectively) and despite its low concentration in Sauvignon wines, 4-mercapto-4-methylpentan-2-one seems to play a major role in the varietal aroma of the wines from this cultivar.

Volatile thiols were purified from a dichloromethane extract of Sauvignon blanc wine by the reversible combination of the thiols with p-hydroxymercuribenzoate, fixation of the resulting complex in an anion exchange column, and finally release of the thiols with cysteine. By analyzing the purified thiol extract from 500 mL of wine, using gas chromatography coupled with mass spectrometry, it was possible to measure the concentrations of five volatile compounds at once:  4-mercapto-4-methylpentan-2-one, 3-mercaptohexyl acetate, 3-mercaptohexan-1-ol, 4-mercapto-4-methylpentan-2-ol, and 3-mercapto-3-methylbutan-1-ol. Analysis of 10 typical Sauvignon Blanc wines (Bordeaux, Sancerre) showed that the first three compounds listed above are expected to be involved in varietal aroma, as they may be present at concentrations greatly in excess of their respective perception thresholds. Keywords: Volatile thiol; aroma; Sauvignon blanc wine; Vitis vinifera; p-hydroxymercuribenzoate