Flavonoid

Flavonoid is a class of plant secondary metabolites that have two benzene rings (each called A-ring and B-ring) connected by a chain of three carbons (Figure 1). The carbon chain, corresponding to the numbers 2,3,4 in Figure 1, can link to a hydroxyl group in the A-ring to form the C-ring. Flavonoid is structurally classified by the modification pattern of this C-ring.

Aurones and Chalcones	Flavanone	Flavone
Dihydroflavonol	Flavonol	Flavan
Anthocyanin	Isoflavonoid	Neoflavonoid

Flavonoid is synthesized through the phenylpropanoid-acetate pathway in all higher plants. It is responsible for many biological activities including pigments, anti-oxidative or anti-allergic agents, and signaling elements in nodule formation. Some of them are quite familiar in our daily life.

Familiar examples. anthocyanin (blueberry), isoflavone (soybean), rutin (soba noodle), catechin (tea), flavan-diol (tea), naringeninchalcone (tomato), polyphenol (wine, cacao)