Evolution of polyfunctional mercaptans and their precursors during Merlot alcoholic fermentation

Polyfunctional mercaptans and their cysteinilated and glutathionilated precursors were analysed in samples taken at different densities during the alcoholic fermentation of five tanks in a two-year study. The aim was to determine when these compounds are extracted, released and degraded during this process. At the beginning of the fermentation, an increase in the concentration of cysteine-3-mercaptohexan-1-ol (CYSMH) and glutathione-3-mercaptohexan-1-ol (GLUMH) was observed, due to the extraction of these precursors from skin to must. Later on a decrease in the concentration was perceived as CYSMH and GLUMH broke up to release the polyfunctional mercaptans and other non-identified compounds. The concentration of polyfunctional mercaptans increased during alcoholic fermentation. There are significant differences in the concentration of all the volatile thiols and its precursors, between samples taken at different moments of the fermentation in each tank. However, even if a large concentration of CYS/GLU precursors in must was released, only a small concentration of polyfunctional mercaptans liberated from them were found in wine. Probably, these compounds are labile and parts of them were degraded during the fermentation process. (C) 2015 Elsevier Ltd. All rights reserved.