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Tannins are widely used in winemaking and food and beverage preparation for the many different contributions they can give to the overall characteristics of the product (e.g., colour stability, mouthfeel and aromatic composition). Varietal thiols and their precursors are one of the most interesting research areas in food science and a lot of effort has been put to further the current understanding on their formation and on the impact of different production strategies on their concentration in the final product. This paper reports the identification of two important thiol precursors (Cys-3MH and GSH-3MH) in commercial grape oenological tannins and, to the best of our knowledge, this information is reported here for the first time. This finding allows potential new perspectives in the winemaking and the food industry, offering the possibility of controlled additions of thiol precursors in pre-fermentative stages in order to tune the aroma profile of fermented products., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Background and Aims Grape 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 Results Müller- Thurgau ( n = 19) and Sauvignon Blanc (32) grapes from Trentino ( Italy) were hand harvested and processed under the following conditions: reductive (air protected; 80 mg/kg sulfur dioxide, 80 mg/kg L-ascorbic acid, and 200 mg/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. Conclusions Both GSH- 3MH and Cys- 3MH were identified for the first time in Müller- Thurgau juices. Oxidative maceration increased the GSH- 3MH concentration in 16 out of 19 Müller- 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 Müller- Thurgau increased GSH- 3MH concentration significantly ( P < 0.01). Significance of the Study This work highlights the complexity of the mechanisms involved in the potential de novo formation of thiol precursors. [ABSTRACT FROM AUTHOR]

We evaluated the impact of a number of clarifying agents on the concentration of S-3- (hexan-1-ol)-L-cysteine (Cys-3SH) and S-3-(hexan-1-ol)-L-glutathione (GSH-3SH). 19 clear grape juices were spiked with a grape skin tannin rich in Cys-3SH and GSH-3SH. Juices were then treated with Na-bentonite, PVPP or charcoal (1 g/L) and cold settled. The concentration of precursors was measured and compared to the corresponding untreated control juices in the devatted samples. Cys-3SH and GSH-3SH were analysed using UHPLC-MS/MS and accuracy was guaranteed with deuterated internal standards. Only charcoal caused a statistically significant depletion of both precursors, quantitatively limited even at the highest dose adopted. Technologically, the clarifiers used in juice affected the thiol precursors in a marginal manner. [ABSTRACT FROM AUTHOR]