Degradation of cyanidin-3-rutinoside and formation of protocatechuic acid methyl ester in methanol solution by gamma irradiation

Abstract Anthocyanins are naturally occurring phenolic compounds having broad biological activities including anti-mutagenesis and anti-carcinogenesis. We studied the effects and the degradation mechanisms of the most common type of anthocyanins, cyanidin-3-rutinoside (cya-3-rut), by using gamma ray. Cya-3-rut in methanol (1 mg/ml) was exposed to gamma-rays from 1 to 10 kGy. We found that the reddish colour of cya-3-rut in methanol disappeared gradually in a dose-dependent manner and effectively disappeared (>97%) at 10 kGy of gamma ray. Concomitantly, a new phenolic compound was generated and identified as a protocatechuic acid methyl ester by liquid chromatography, 1 H, and 13 C NMR. The formation of protocatechuic acid methyl ester increased with increasing irradiation and the amount of protocatechuic acid methyl ester formed by decomposition of cya-3-rut (20 μg) at 10 kGy of gamma ray was 1.95 μg. In addition, the radical-scavenging activities were not affected by gamma irradiation.