Occurrence of Astringent Oligomeric Proanthocyanidins in Legume Seeds

The distribution of oligomeric proanthocyanidins in legume seeds was investigated in connection with organoleptic astringency. The seeds contained various kinds of oligomers (dimers˜hexamers). The total oligomer contents were at least 0.040% in azuki beans, 0.017% in black soybeans, 0.005% in mung beans and a trace amount in regular soybeans. Each aliquot of aqueous solution of partially purified proanthocyanidin oligomers tasted astringent even at a concentration of 0.001% (w/v). The possible contribution of oligomeric proanthocyanidins and polymeric proanthocyanidins to the astringent off-taste of legume seeds is discussed.