Formation of novel GSH-tannin adducts during red wine aging: Detection and identification using targeted...

Astringency in red wine is primarily caused by condensed tannins interaction with salivary proteins, thus contributing to wine mouthfeel. Condensed tannin cleaves in the presence of acid, and the reactive electrophilic intermediates react largely with tannin, the most abundant nucleophiles, re-forming tannin, but may react with others. Here we hypothesize that glutathione (GSH) interacts with the C4-carbocations formed during acid-catalyzed depolymerization of tannins in red wine, forming glutathionyl-flavan-3-ol adducts. Using targeted LC-QToF-MS analysis, glutathionyl-flavan-3-ol adducts at the tannin linkage are reported in wine for the first time. Studying 24 Washington red wines aged between 1 and 20 years of age, the highest amounts for these adducts were observed in 1-year-old wines followed by losses as wines aged. The impact of glutathione supplementation on adduct formation was tested in experimental Cabernet Sauvignon wines, showing a five-fold increase in adduct concentration compared to controls after one year of bottle ageing. Additionally, a reduction in protein-precipitable tannins was observed for model solution and supplemented wines, suggesting that glutathionyl-flavan-3-ol adducts might contribute to reduced astringency perception in aged wine. Future studies are needed to confirm the stability of these adducts and explore their sensory effects on wine mouthfeel.