Glutathione content evolution during spontaneous alcoholic fermentations of Sangiovese grapes
Abstract
Glutathione is a tripeptide (γ-Glu-Cys-Gly), which can occur in grapes, in must and in wine prevalently in the reduced form as well as in the oxidized form as glutathione disulfide. The importance of the reduced form of glutathione lies in its antioxidant activity. In must, it limits browning by reducing o-quinones produced by polyphenol oxidase activity on hydroxycinnamic acids; in wine, it exerts a protective effect on various aromatic compounds. Glutathione concentration in wine is lower than in grape juice and variable as it depends on several factors, ranging from the native content of grapes to winemaking technique. During alcoholic fermentation, Saccharomyces cerevisiae metabolism modifies to different extent the native concentration of glutathione in must, depending on the strain. In this study, the evolution of the glutathione content during three spontaneous alcoholic fermentations of Sangiovese grapes (vintage 2015), carried out at commercial-scale in a winery located in Val d’Orcia (Tuscany), was monitored. From a microbiological point of view, S. cerevisiae dominated all the fermentation phases, since non-Saccharomyces yeast did not reach significant population densities. However, a great intraspecific genetic diversity was found within the S. cerevisiae populations. In freshly pressed musts, glutathione concentration ranged from 4 to 7mg/L, and consisted predominantly of the oxidized form. During alcoholic fermentation, glutathione concentration resulted highly variable: in the first days, in correspondence of yeast exponential growth phase, it decreased, possibly due to the consumption of glutathione by yeast cells in the active growth phase; successively, glutathione content increased until the end of alcoholic fermentation, suggesting a glutathione release from yeast cells in correspondence to cell autolysis into the wine; at the end of alcoholic fermentation, glutathione contents of wines ranged from 19 to 23mg/L, and the reduced form represented about 60% of the total. The results suggest that the final glutathione concentration in wine is mostly dependent on the amount of glutathione released by yeast cells rather than on that derived from grapes at the vintage.
Issue: Macrowine 2016
Type: Poster
Authors
*Food Micro Team