Updated insights into esterified Flavan-3-ols in grapevine and wine: Origin, transformation, and taste response of epicatechin-3-O-vanillate and -3-O-gallate.

Esterified flavan-3-ols, prevalent in grapes and wine as monomers or subunits within condensed tannins, significantly influence the mouthfeel of wine. However, comprehensive knowledge of their molecular structures and transformations during vinification is still limited. This study investigated tannin derivatives, specifically vanillate and gallate forms, using UHPLC-Q-TOF to elucidate their distribution across four Vitis vinifera L. cultivars, their transformations during vinification, and their metabolic fate mediated by Oenococcus oeni and β-glucosidase activity. The taste responses of epicatechin-3-O-vanillate (ECV) and -3-O-gallate (ECG) were evaluated using an electronic tongue. The results indicated that ECV was predominantly found as monomers and terminal units within the condensed tannins across all examined grape varieties. During early malolactic fermentation (MLF), ECV and ECG are hydrolyzed into epicatechin (EC), vanillic acid (VA), and gallic acid (GA) by O. oeni and β-glucosidase enzymes. This enzymatic cleavage is potentially correlated with reduction of esterified flavan-3-ols contentand perceptible bitterness in wine.