Cork and Wine: interactions and newly formed compounds

When the cork is in direct contact with an alcoholic solution such as in case of a bottle wine, some cork components can migrate into the wine. Volatile and non-volatile compounds soluble in ethanol/water such as carbohydrates, alcohols, ketones, phenolic compounds including tannins that were already proved to pass from cork to wine, are of oenological importance due to their contribution to sensory properties (color, flavor, astringency and bitterness). There is an oenological interest regarding wood barrels since it has been demonstrated that they could also impact on wine organoleptic properties (aroma, color and taste) during oak ageing.Cork stoppers are believed to participate in the same interactions, as the nature of the compounds that are able to pass to wine are from the same families but depend on the contact time, the bottle position during storage and on the type of cork.This work has as main propose to study the interections between compounds extracted from cork by wine model solutions and the evaluation of the reactivity of these with two main classes of compounds present in red wines, namely flavan-3-ols ((+)-catechin) and anthocyanins (Malvidin-3-O-glucoside). With this information, the winemakers can choose varieties of cork stoppers to upgrade wine quality during storage and ageing.This work consisted on studying the reaction in wine model solution (12% ethanol, pH 3.2) of phenolic compounds like phenolic acids, aldehydes and tannins with (+)- catechin and malvidin-3-O-glucoside. From these reactions, different compounds were formed: 
i) Pinotins (Pyranomalvidin3glucoside- Catechol and Pyranomalvidin3glucoside- Guaiacol);ii) Xanthylium Salts (formed by two catechins units and vanillin);
iii) Dimer Catechin-Vanillin-Catechin;iv) Corklins (this new compound results from interaction between ellagitannins in alcoholic solutions, yielding an ethanolic derivate, and (+)-catechin;v) Acutissimin;vi) Catechin-Caffeic acid adduct. The newly found compound was detected and identified in these reactions with an ion mass in negative mode at m/z 467, with a fragmentation pattern compatible with the loss of -44 units (acid), -178 units (caffeic acid), -152 (Retro Diels Alder, characteristic of catechin).The struture of the (+)-catechin-caffeic acid adduct was determined by NMR (1H, COSY, HSQC and HMBC).

Authors: Azevedo Joana1, Oliveira Joana1, Lopes Paulo2, Mateus Nuno3 and De Freitas Victor3

1Faculty of Science the University of Porto, Rua Campo Alegre S/N, 4169-007 Porto, Portugal
2Amorim & Irmãos, Rua Corticeiros, 4536-904 S M Lamas, Portugal
3FCUP- Chemistry and Biochemistry Department of Faculty of Science University of Porto

*corresponding author: joana_c_azevedo@msn.com

keywords: Cork, Wine, Polyphenols, Reactivity, Catechin-Caffeic acid adduct

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