Evolution of Flavanol Glycosides during Red Grape Fermentation

Abstract

Monomeric and dimeric flavanol glycosides were quantified by UHPLC-MRM in Syrah (SYR) and Grenache (GRE) grapes and in their corresponding wines for the first time. Quantities were extremely variable depending on grape tissue (seeds or skins) and during fermentation. Overall, 22 monomeric and dimeric mono- and diglycosides were determined with concentrations ranging from 0.7 nanograms to 0.700 micrograms per gram of grape tissue, and 0 to 60 micrograms per liter for wines. The evolution of the glycosides’ composition during winemaking suggests that almost all these compounds originate in the grapes themselves and display different extraction kinetics during winemaking. One isomer of the monomeric (epi) flavanol monoglycosides seemed to be biosynthesized by yeasts during wine fermentation. The sharp decrease in concentration of some isomers at the late stages of fermentation or after pressing suggests that some grape glycosidase activities convert these compounds into non-glycosylated flavanols.

Flavanol Glycoside Content of Grape Seeds and Skins of Vitis vinifera Varieties Grown in Castilla-La Mancha, Spain

“…These types of compounds were previously reported for Merlot, Tannat, and Syrah grapes, where ten (epi)catechin monodiglycosides were identified in skins and seeds [19].…”

“…A total of nine MDG’s were previously reported in seeds of several grape varieties, [19]. However, in this study one of the four compounds previously identified was also detected in grape skins, i.e., peak 21 (20.7 min.).…”

“…This may be due to the effect of external factors such as environmental conditions which affect the biosynthesis of flavonoids [7]. Furthermore, previous studies reported that the MMG concentration depends on the degree of berry maturity, where the concentration of monomeric flavanol monoglycosides decreases during grape ripening [19].…”

“…Glycosylated hexoside forms of flavanols have been described in Merlot, Syrah, Tannat, and Cabernet Sauvignon grapes [17,18], of which a substantial number consisted of monoglycoside and diglycoside derivatives of flavanol monomers and dimers, highlighting the diversity of these compounds. The concentration of glycosylated flavanols in grapes depends on variety and maturity, and where they occur in the berries [18,19]. During ripening, the concentration of monomeric flavanol monoglycosides decreases and those of diglycoside forms increase until veraison is reached [19].…”

“…The concentration of glycosylated flavanols in grapes depends on variety and maturity, and where they occur in the berries [18,19]. During ripening, the concentration of monomeric flavanol monoglycosides decreases and those of diglycoside forms increase until veraison is reached [19]. The role of flavanol glycosides in plant metabolism remains to be elucidated, but studies suggest they might contribute to the formation of proanthocyanidins [20,21] and behave as markers of seed or skin extraction during fermentation [18].…”