Anthocyanidins are common plant pigments. They are the sugar-free counterparts of anthocyanins based on the benzopyrylium (chromenylium) ion. They form a large group of polymethine dye. In particular anthocyanidins are salt derivatives of the 2-phenylchromenylium cation, also known as flavylium cation. As shown in the figure below, the phenyl group at the 2-position, can carry different substituents. The counterion of the flavylium cation is mostly chloride. With this positive charge, the anthocyanidins differ from other flavonoids.
Anthocyanidin can be extracted from Grape seed, Cranberry, Pine bark, Bilberry, and etc. In other words, Anthocyanidin is the active ingredient of Grape seed extract, Cranberry extract, Pine bark extract, and Bilberry extract and so on.