Figure 1.

Examples of the chemical structures of tannins present in different tannin subgroups. Hydrolyzable tannins can be divided into simple gallic acid derivatives (A, pentagalloylglucose), gallotannins (B, decagalloylglucose), monomeric ellagitannins (C, tellimagrandin II), and oligomeric ellagitannins (D, oenothein A). Proanthocyanidins can be divided into oligomeric proanthocyanidins (E, PCPD dimer made of catechin and epigallocatechin) and polymeric proanthocyanidins (F, 28-meric PCPD polymer). The proanthocyanidins always contain one terminal unit at the bottom of the structure and one or more extension unit on the top of that.