Ethylidene-bridged flavan-3-ols in red wine and correlation with wine age

Condensed tannins are responsible for astringency and bitterness and participate in the color stability of red wines. During wine making and aging, they undergo chemical changes including, for example, acetaldehyde-induced polymerization. Following this study, the ethylidene-bridged flavan-3-ols were monitored in different vintage wines made from grapes collected in the same vineyard in three wineries in Bordeaux, Pauillac, and Saint Julien. Flavan-3-ol ethylidene bridges were quantified by wine 2,2'-ethylidenediphloroglucinol (EDP) phloroglucinolysis. This method was based upon the analysis of EDP, a product formed after acid-catalyzed cleavage of wine flavan-3-ols in the presence of excess phloroglucinol. The flavan-3-ol ethylidene bridges were then compared to flavan-3-ol contents (phloroglucinolysis), phenolic contents, and color measurements. Low amounts of flavan-3-ol ethylidene bridges (0.8-2.5 mg L-1) were quantified in wines. Flavan-3-ol ethylidene bridges represent less than 4% of flavan-3-ol bonds, but the proportion of these linkages relative to native interflavan bonds increased with wine age. This proportion correlated with pigmented polymers.