Varietal thiol precursors in Gewürztraminer: effect of clone and grape ripening.

Much research has been carried out since the discovery of glutathionyl- (GSH-) and cysteinyl (Cys-) precursors of 3-mercaptohexan-1-ol (3MH) in grapes and juices (Tominaga et al.,1998; Peyrot des Gachons et al., 2002) in order to understand the origin of these precursors and optimize the technological options useful to liberate and maintain the free forms and the related fermentative compounds characterised by interesting tropical, passion fruit and grapefruit-like aroma. As few data are available about the role of these precursors in the case of Gewürztraminer (GWT; Roland Dubordieu and Tominaga 2009; Roland et al., 2010a & b; Concejero et al., 2014), an international variety native to Tramin (South-Tyrol, Italy) we investigated the effect of clone and ripening in grape samples of GWT grown in Trentino (Italy). The juices of 7 GWT clones - ISMA-AVIT 904, 906, 916, 918 and 920R, as well as LB14 and 1101 - grown in 4 plots and harvested at the technological ripeness allowed by the very hot 2015 vintage were analysed. Moreover, GWT grapes from 6 different non-clonal vineyards sited at a altitude between 120 and 525 m a.s.l. in Trentino were analysed during the last month before harvest. Thiol precursors were measured using an UHPLC approach with triple quadrupole mass detection according Larcher et al., (2013). Significant differences were found between clones as regards thiol precursors concentration in 2015 grape, the 906 and 920R clones showing a higher molar concentration of the sum of GSH-3MH and Cys-3MH compared to 916. A clear and statistically significant increasing trend during ripening was observed for the cited precursors, confirming for GWT previous results observed by Kobayashi et al (2010) for Koshu.