Glutathione and Its Application in Winemaking

Glutathione (GSH) is important in wine because it has the ability to scavenge ortho-quinones, main protagonists of color browning and aroma loss due to oxidation mechanisms. Because it has a very low oxydoreduction potential (E’o=-250 mV at pH 7.0 ; E’o=-40 mV at pH 3.0), it can act as a strong buffer in many cellular oxydoreduction reactions. It has been known for years that it is a more potent anti-oxidant than ascorbic acid (E’o=+60 mV at pH 7.0 ; E’o=+267 mV at pH 3.0). It then plays a critical role in preventing the oxidation of must phenols as it can react via its –SH group with caftaric acid – one of the most susceptible phenols to oxidation in musts and generate Grape Reaction Product (GRP) which is a stable and colorless compound (Moutounet et al, 2001). Notably, this mechanism has been shown for GSH and not for the other compounds present in must or in yeast, and possessing SH-group (such as cystein or glutamyl-cystein for instance).