Identification of γ-nonalactone precusor in Merlot and Cabernet-Sauvignon grapes

Abstract

Wine flavor results on complexes interactions of odorous components, which come from different aromatic families like esters, thiols, aldehydes, pyrazines or lactones. Varietal lactones identified in red wines contribute to cooked fruity flavors such as dried peach, apricot, figs and dried prune. Recent studies have demonstrated the key impact of the harvest date on the lactone content in wine. The influence of the temperature during grape ripening was also underlined. Many lactones have been detected in wines, but one of them, gamma-nonalactone, possesses a low detection threshold (Dth 27 µg/L), and has been detected at high concentration in wine (up to 200 µg/L). Thus, it contributes directly to the cooked peach flavors in red wines. All these observation led us to investigate the chemical and biochemical mechanisms associated with gamma-nonalactone formation in must from Merlot and Cabernet-Sauvignon grapes, a LC-MS/MS method was developed and validated. 4-oxononanoic acid is identified for the first time in must sample whereas its concentration was ranged from some µg/L to more than 60 µg/L. Additionally, in order to demonstrate the impact of alcoholic fermentation on the formation of gamma-nonalactone, we synthesized labeled d6-4-oxononanoic acid and observed a positive correlation between d6-4-oxononanoic acid concentration added and d6-gamma-nonalactone formed in spiked samples.In conclusion, our results demonstrated the presence of 4-oxononanoic acid in must and its biotransformation to gamma-nonalactone during alcoholic fermentation of red grape varieties. We validate for the first time its role of precursor of the odorous gamma-nonalactone in wine