Glutathione is a tripeptide formed by three amino-acidic units: glutamic acid, cysteine and glycine. It is normally found in equilibrium between the reduced (GSH) and the oxidized form (GSSH, as a Bisulphide). It is present in plants and foods, such as fruits like grapes.
Glutathione is a very delicate component though, and it can be strongly reduced in concentration by some procedures on the field or in the cellar, such as pressing and clarification. On the field it is necessary to keep in grapes an optimal concentration of nitrites and to reduce the copper concentration.
Typically, as shown by Fracassetti and Tirelli of the Department of Food and Microbiology Science and Technology of the Milan University, the concentration of GSH in wine is a lot lower than the grape one because of the pressing, even if inert pressing procedures are employed. Following yeast administration, GSH concentration increases to 35 mg/l circa, given a ready assimilable nitrogen concentration for the yeast of 200 mg/l. The GSH concentration in the must can be decreased by the presence of copper in the grapes and can be increased by the availability of oxygen during the processing. However, the strain of yeast employed seems not to affect the GSH concentration in wine.
In the context of sulfur dioxide-free winemaking in white these information are extremely important since the employment of glutathione-rich coadjutants, such as inactivated yeasts, should respect some preconditions.
According to a research by the San Michele all’Adige Institute in Italy, glutathione is able to ameliorate the aromatic profile of Sauvignon Blanc, preserving citrus aromas, such as grapefruit, that represent the fruity notes of fresh wines. By employing compounds such as glutathione, the undesirable molecules decreases, while the compounds typical of Sauvignon are increased. The study demonstrated that adding 10 mg/l of glutathione during wine maturation allows the fruity notes to be maintained until three years of ageing in white wines. Moreover, the adding of 20 mg/l of glutathione to red wines strongly reduces oxidation, which is detrimental to a proper aging process.