Fruity/tropical sulfur aroma precursors in hybrid grapes

In the last century, several hybrid grape varieties were produced in order to overcome pest (phylloxera) and vine diseases, such as downy, powdery mildew. As they are not currently used to any significant extent either for wine-making in Europe, for technological and legal reasons (European Community Regulation, 1998) or for edible purposes, they are little studied and relegated to germplasm collections. However, there is a renewed interest for many of these varieties, due to their richness of secondary metabolites. As a matter of fact, the chemical metabolites of these grapes are often qualitatively and quantitatively superior to V. vinifera varieties. For instance, recent studies showed that several hybrids are very rich in monoglucoside and diglucoside anthocyanins [De Rosso et al., 2012], flavonol glycosides [De Rosso et al., 2014], and have relevant contents of trilinolein [De Marchi et al., 2012]. Varietal thiols (e.g. 3-mercaptohexan-1-ol; 3-mercaptohexyl acetate; 4-mercapto-4-methylpentan-2-one), belonging to an important class of aroma compounds characterized by extremely low sensory threshold, can impart strong tropical and citrus-like sensory notes to wine. Their occurrence in wine is related to the presence of non-volatile S-glutathionylated and S-cysteinylated precursors in grapes, even if other alternative pathways of synthesis have been proposed. Moreover, the cleavage of the S-cysteinylated precursors caused by mouth bacteria suggests a direct retronasal contribution of this precursors also in unfermented beverages [Starkenmann et al., 2008]. This study presents for the first time a detailed survey on the varietal thiol precursors in hybrid grapes with the aim of giving support to possible new uses in soft drinks and low-alcohol beverages production