Sauvignon blanc metabolomics: grape juice metabolites affecting the development of varietal thiols and other aroma compounds in wines

The pathway for the biogenesis of varietal thiols, such as 3-mercaptohexanol (3MH), 3-mercaptohexyl acetate (3MHA) and 4-mercapto-4-methylpentan-2-one (4MMP) in Sauvignon blanc (SB) wines is still an open question. Varietal thiol development requires yeast activity, but poor correlation has been found between thiols and their putative respective precursors. This research is the first application of metabolomics to unravel metabolites in the grape juice that affect the production of varietal thiols in wines. Comprehensive metabolite profiling of 63 commercially harvested SB juices were performed by combining gas chromatography–mass spectrometry and nuclear magnetic resonance spectroscopy. These juices were fermented under controlled laboratory conditions using a commercial yeast strain (EC1118) at 15 °C. Correlation of thiol concentration in the wines with initial metabolite profiles identified 24 metabolites that showed positive correlation (R > 0.3) with both 3MH and 3MHA, while only glutamine had positive correlation with 4MMP. Subsequently, we carried out juice manipulation experiments by adding subsets of these 24 metabolites in a 2011 SB grape juice in order to validate the hypotheses generated by metabolomics. The juice manipulation results confirmed metabolomics hypotheses and revealed grape juice metabolites that significantly impact on the development of three major varietal thiols and other aroma compounds of SB wines.