Analysis of Ethylidene-Bridged Flavan-3-ols in Wine

Abstract

A method was developed to determine the amount of ethylidene-bridged flavan-3-ols in wine. The method was based upon the analysis of 2,2‘-ethylidenediphloroglucinol (EDP), a product formed after acid-catalyzed cleavage of wine flavan-3-ols in the presence of excess phloroglucinol. In the developed analytical method, the wine was purified and concentrated using C₁₈ solid-phase extraction before the phloroglucinolysis reaction was carried out. This procedure was used to quantify ethylidene-bridged flavan-3-ols in wine and the molar ratio between ethylidene-bridged linkages and native interflavan linkages. The method validation showed 9.2% repeatability. The recovery of the ethylidene-bridged flavanols in wine was 90% for concentrations up to 4.5 mg·L^-1 of ethylidene-bridged linkages, and it decreases to 83% above and until the concentration reached 7.6 mg·L^-1. Initial results showed that the concentration of ethylidene-bridged flavan-3-ols measured in wines was very low (less than 1.3 mg·L^-1) and that they represented less than 1.3% of the total interflavonoid linkages on a molar ratio. Keywords: Tannins; flavan-3-ol; ethylidene bridge; red wine; aging; 2,2‘-ethylidenediphloroglucinol; EDP; phloroglucinolysis