Characterisation of proanthocyanidins from black soybeans: Isolation and characterisation of proanthocyanidin oligomers from black soybean seed coats

Proanthocyanidin oligomers (dimers to tetramers) were isolated from black soybean seed coats, using Sephadex LH-20 column chromatography and reversed-phase preparative HPLC. The isolated oligomers consisted of only (−)-epicatechin units, which were linked through either 4β→8 or 4β→6 (B-type) bonds. Procyanidin B2, procyanidin C1, and cinnamtannin A2 were identified as the main compounds of the proanthocyanidin dimers, trimers, and tetramers, respectively.