About the impact of oak ellagitannins on wine odoriferous thiols under acidic and oxidation conditions. Issue 20 (20th May 2015) - Petit, Emilie
Abstract: The decrease of the level of characteristic odoriferous thiols in wines has been in part imputed to chemical transformations that take place during aging of wines in oak-made barrels and subsequent storage in bottles. Oxygen dissolved in wines certainly plays a role in such chemical transformations, such as the oxidation of catecholic catechins into thiol-trapping ortho -quinones. However, wines aged in barrels or supplemented with oak chips contain pyrogallolic C -glucosidic ellagitannins, which can also trap thiols in mildly acidic and oxygenated wine solutions by both nucleophilic substitution and oxidative addition reactions. The C -glucosidic ellagitannin vescalagin and methyl gallate were chosen as substrates to investigate these reactions in the presence of two well-known wine odoriferous thiols, 3-sulfanylhexan-1-ol (3SH) and 2-furanmethanethiol (2FMT). Three novel thio-vescalagin condensates were thus hemisynthesized under acidic conditions, and the FeCl3 -mediated oxidation of methyl gallate furnish different thiogallate adducts under conditions applicable to the oxidative hemisynthesis of thio-ellagitannin adducts. Graphical abstract: