Fig. 1. Chemical structure of the studied monomers (a) and condensed tannins linked by the C4–C8 (b) or C4–C6 (c) interflavanol bonds. Apple condensed tannins are made of
epicatechin units linked by C4–C6 or C4–C8 interflavanol bonds, whereas grape seed tannins are made of catechin, epicatechin, and epicatechin gallate.