Isolation of Dopamine and Browning of Tubers of Chinese Yam (Dioscorea batatas)

Abstract

In the methanol extract from aerial tubers of chinese yam, dopamine (3, 4-dihydroxyphenylethylamine), catechins and associated tannins were detected by two dimensional paper chromatography.
The polyphenolic substances were adsorbed on Amberlite C G 120 resin and followed by the successive elution with pH 7 phosphate buffer solution and 3 N hydrochloric acid. From the latter effluent, a colorless crystal was isolated. The isolated crystal was identified as dopamine hydrochloride, since it had the same melting point, values of the elementary analysis, U V and I R spectrum as the latter compound.
Polyphenol oxidase prepared from the tubers of chinese yam showed high activity for the isolated dopamine. Therefore, it is likely that dopamine is a principal browning compound of the yam tubers. Other polyphenols also may take parts in the browning of the tubers.