Measuring the Aromatic Potential of Vitis vinifera L. Cv. Sauvignon Blanc Grapes by Assaying S-Cysteine Conjugates, Precursors of the Volatile Thiols Responsible for Their Varietal Aroma

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Abstract
The method presented for measuring the aromatic potential of Sauvignon blanc must is based on an assay of the S-cysteine conjugate precursors of three volatile thiols involved in the characteristic aroma of wines made from this grape variety: 4-mercapto-4-methylpentan-2-one, 4-mercapto-4-methylpentan-2-ol, and 3-mercaptohexan-1-ol. These compounds were released enzymatically from their precursors by percolating the must through an immobilized tryptophanase column (EC 4.1.99.1), catalyzing an α,β-elimination reaction on the S-cysteine conjugate. The volatile thiols were analyzed by GC-MS, as were the deuterated analogues that had been released from synthesized deuterated precursors and were added as internal standards. The quantities of volatile thiols released under these conditions were proportional to the S-cysteine conjugate content of the must. Keywords: Aroma potential; S-cysteine conjugate; flavor precursor; Sauvignon blanc; stable isotope dilution assay; tryptophanase; Vitis vinifera