Influence of oxygen availability during skin-contact maceration on the formation of precursors of 3-mercaptohexan-1-ol in Muller-Thurgau and Sauvignon Blanc grapes

Background and AimsGrape maceration plays an important role in the formation of precursors of 3-mercaptohexan-1-ol (3MH), 3-S-glutathionyl mercaptohexan-1-ol (GSH-3MH) and 3-S-cysteinyl mercaptohexan-1-ol (Cys-3MH), but its contribution is still not well understood. The aim of this paper was to study the effect of oxygen deprivation on the concentration of these 3MH precursors during skin-contact maceration in two grape cultivars. Methods and ResultsMuller-Thurgau (n=19) and Sauvignon Blanc (32) grapes from Trentino (Italy) were hand harvested and processed under the following conditions: reductive (air protected; 80mg/kg sulfur dioxide, 80mg/kg L-ascorbic acid, and 200mg/kg dimethyl dicarbonate) and oxidative (no addition of adjuvants and air contact). After maceration, GSH-3MH and Cys-3MH were analysed by liquid chromatography-mass spectrometry and isotopic dilution. ConclusionsBoth GSH-3MH and Cys-3MH were identified for the first time in Muller-Thurgau juices. Oxidative maceration increased the GSH-3MH concentration in 16 out of 19 Muller-Thurgau and in 23 out of 32 Sauvignon Blanc juices, while Cys-3MH was higher in 13 and 20 juices, respectively, of the two cultivars. Parametrical and non-parametrical statistical tests confirmed that oxidative maceration of Muller-Thurgau increased GSH-3MH concentration significantly (P<0.01). Significance of the StudyThis work highlights the complexity of the mechanisms involved in the potential de novo formation of thiol precursors.