Structures of proanthocyanidins and monomeric subunits. A generic structure of proanthocyanidin is shown and the possible configurations are highlighted in colour. "n" indicates the number of extension units, variable according to plant species and tissues. The general chemical structure of PA monomeric subunit includes a C6-C3-C6 skeleton which is called the A-C-B rings. The carbon nomenclature is indicated as numbers next to the corresponding carbon. The B-ring generally bears two or three hydroxyl groups. According to the stereochemistry of carbons 2 and 3 on the C-ring, the PA monomeric subunit could be in 2,3-trans (e.g. (+)-catechin) or in 2,3-cis configuration (e.g.(-)-epicatechin). The structure of galloyl is shown next to PA generic structure. The right column denotes the subunits studied in this work where "Ex" indicates "extension" units and "T", terminal subunits/monomers. n.d., not detected.