Identification and quantification by LC-MS/MS of a new precursor of 3-mercaptohexan-1-ol (3MH) using stable isotope dilution assay: Elements for understanding the 3MH production in wine

The isotopically labelled S-3-(hexan-1-ol)-glutathione d(2)/d(3) (G(3)MHd(2)/d(3)) was synthesized with a strategy based on acid-labile protecting groups. The natural analogue of this compound could be a precursor of 3-mercaptohexanol, a varietal thiol reminiscent of grape fruit, released during alcoholic fermentation. In a first time, deuterated glutathione conjugate was used to perform identification and quantification by stable isotope dilution assay of G3MH in musts from several varieties: Sauvignon, Riesling and Gewurztraminer. In a second time, synthetic and natural musts (Sauvignon Blanc) were spiked by G(3)MHd(2)/d(3) at different levels from 12 to 150 mu g L(-1) to demonstrate the relationship between 3-mercaptohexan-1-ol (3MH) and G3MH. GC-ITMS/MS analysis of the resulting wines clearly showed the formation of the corresponding deuterated 3MH, that proves the direct connection with G3MH under enological conditions. in Sauvignon Blanc grape juice, a conversion yield of 4.4% was found in duplicate for an initial spiking of G3MH d(2)/d(3) equivalent to 12 mu g L(-1). (C) 2010 Elsevier Ltd. All rights reserved.