Studies on the acetaldehyde-induced condensation of (-)-epicatechin and malvidin 3-O-glucoside in a model solution system

The reaction between (-)-epicatechin, malvidin 3-O-glucoside, and acetaldeh yde was studied in a model solution system. Ethyl-linked flavanol oligomers and anthocyanin-flavanol derivatives were observed, showing that the two p olyphenols competed in the condensation process. Among the anthocyanin-ethy l-flavanol adducts, dimeric compounds in which the flavanol was linked to t he anthocyanin with CH3-CH bridges were observed. In addition, trimeric and tetrameric products containing one anthocyanin and one, two, or three flav anols 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 t hat only one anthocyanin A ring summit can be included in the polymerizatio n process, which thus stops when both ends are occupied by an anthocyanin m oiety. Thioacidolysis of the two isolated anthocyanin-ethyl-flavanol dimeri c derivatives showed that anthocyanin-ethyl linkage was not sensitive to su ch reactants, whereas the flavanol-ethyl one was. In addition, flavanol-eth yl linkages involved in anthocyanin-ethyl-flavanol adducts were found to be less sensitive to those involved in flavan-ethyl dimers.