Résumé
Saccharomyces cerevisiae can make use of a nonproteogenic amino acid, gamma-aminobutyric acid (GABA), one of the various nitrogen sources present in grape juice. The effect of this amino acid on yeast fermentation kinetics and by-product formation in winemaking was investigated. The GABA content of musts ranged from 2 to 580 mg/L as a function of variety, year, and geographic origin of the grapes. The gamma-amino acid content may account for up to 20% of the assimilable nitrogen in grape juice. The commercial wine yeast efficiently metabolized exogenous GABA during wine fermentation. The assimilation of this gamma-amino acid increased yeast growth, fermentation rate, and glycerol production, but only when nitrogen was limiting. Results demonstrate that GABA can act as a source of succinate in wine, regardless of the total nitrogen content of the Must. During fermentation, succinate is primarily produced from sugars via the reductive and oxidative branches of the tricarboxylic acid cycle. The yield Of succinate from GABA ranged from 0.75 to I mol succinate/mol GABA as a function of yeast genetic background. Up to 50% of succinate in wine may be derived from GABA, depending on the initial concentration in grape juice. These results provide new insight into GABA metabolism and offer an opportunity to improve the control of wine acidity.