Innovative analysis of 3-mercaptohexan-1-ol,3-mercaptohexylacetate and their corresponding disulfides in wine by stable isotope dilution assay and nano-liquid chromatography tandem mass spectrometry

Both 3-mercaptohexan-1-ol (3MH) and 3-mercaptohexyl acetate (3MHA) were largely studied for the last 20 years due to their pleasant olfactory notes conferred to wine. Until now, many analytical methods focused only on the free forms of both 3MH and 3MHA in wine that provided partial information in the wine aroma evolution. Our study proposes new analytical measurements which allow quantification of both free and disulfide forms of 3MH and 3MHA to better understand the redox phenomenon occurring in wines and further, to orientate wine aroma evolution. Free thiols were analyzed by an original method based on maleimide derivatization allowing in-situ disulfide reduction followed by SIDA-LC-MS/MS analyses exhibiting excellent performances. Indeed, the accuracy ranged from 95 to 110% in three different wine matrices and the repeatability and intermediate reproducibility were inferior to 15% (RSD measurements). Our method exhibited very low limits of detection, which are below to 0.5 ng/L and inferior to the perception thresholds of both compounds. Then, this method was applied to three different wines exposed to several oxidative conditions. On the one hand, it was demonstrated that copper sulfate treatment firstly destroyed the total amount of free 3MH to the benefit of thioether and disulfides compounds, with proportions that could be slightly modified by glutathione addition. On the other hand, oxygenation of wines resulted in partial free 3MH destruction to the benefit of thioether compounds. We proposed for the first time an innovative analysis that gives a complete picture of wine aroma, which can be really useful to winemakers to manage wine aroma evolution and to take advantage of the disulfide reservoir. (C) 2016 Elsevier B.V. All rights reserved.