Analysis of precursors to wine odorant 3-mercaptohexan-1-ol using HPLC-MS/MS: resolution and quantitation of diastereomers of 3-S-cysteinylhexan-1-ol and 3-S-glutathionylhexan-1-ol.

A method has been developed and validated for the analysis of the individual diastereomers of 3-S-cysteinylhexan-1-ol (Cys-3-MH) and 3-S-glutathionylhexan-1-ol (Glut-3-MH) extracted from grape juice and wine. The method uses stable isotope dilution analysis (SIDA) combined with solid-phase extraction (SPE) and reversed-phase high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) for quantitation. These compounds have been considered as potential precursors to the important wine odorant 3-mercaptohexan-1-ol (3-MH). This constitutes the first analytical method where (1) Glut-3-MH has been accurately quantified in grape juice and wine and (2) the individual Cys- and Glut-3-MH diastereomers were separated and quantified by a single HPLC-MS/MS method. The use of deuterium-labeled internal standards has resulted in an accurate and precise method that can achieve quantitation limits of <0.5 microg/L for the individual Cys- and Glut-3-MH diastereomers in grape juice and white wine. The method has been applied to the determination of 3-MH precursor diastereomers in various white juice and wine samples. Overall, Glut-3-MH was always more abundant than Cys-3-MH in the juices and wines examined, regardless of grape variety. Stereochemically, (S)-Glut-3-MH generally dominated over the (R)-diastereomer in the juices and wines, but there was not such a marked difference between the distribution of Cys-3-MH diastereomers. These results have important implications for understanding the formation of wine flavor, and the application of this method will allow further exploration of precursors to the varietal thiol 3-MH.