Studies on the Acetaldehyde-Induced Condensation of (−)-Epicatechin and Malvidin 3-O-Glucoside in a Model Solution System

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Abstract
The reaction between (−)-epicatechin, malvidin 3-O-glucoside, and acetaldehyde was studied in a model solution system. Ethyl-linked flavanol oligomers and anthocyanin−flavanol derivatives were observed, showing that the two polyphenols competed in the condensation process. Among the anthocyanin−ethyl−flavanol adducts, dimeric compounds in which the flavanol was linked to the anthocyanin with CH3−CH bridges were observed. In addition, trimeric and tetrameric products containing one anthocyanin and one, two, or three flavanols units were detected. A tetrameric product containing two anthocyanin and two flavanol units was also found as a doubly charged ion. No compound containing more than two malvidin 3-O-glucosides was detected, suggesting that only one anthocyanin A ring summit can be included in the polymerization process, which thus stops when both ends are occupied by an anthocyanin moiety. Thioacidolysis of the two isolated anthocyanin−ethyl−flavanol dimeric derivatives showed that anthocyanin−ethyl linkage was not sensitive to such reactants, whereas the flavanol−ethyl one was. In addition, flavanol−ethyl linkages involved in anthocyanin−ethyl−flavanol adducts were found to be less sensitive to those involved in flavan−ethyl dimers. Keywords: (−)-Epicatechin; malvidin 3-O-glucoside; acetaldehyde; condensation; thiolysis; LC/DAD; LC/MS