Effect of gamma irradiation on the pigments and the biological activities of methanolic extracts from leaves of centipedegrass (Eremochloa ophiuroides Munro)

Extracts from centipedegrass (Eremochloa ophiuroides Munro) have been previously identified as having beneficial effects medically and cosmetically. In this study, the effects of gamma irradiation on pigment removal and biological activities of centipedegrass extracts to promote industrial application were investigated. The methanolic extracts were exposed to gamma irradiation at dose ranging from 2 to 20 kGy. The major pigments of centipedegrass extracts, cyanidin-3-O-glucoside and cyanidin-3-O-(6″-malonyl-)glucoside, were found to be effectively removed by gamma irradiation above 10 kGy. Although the reddish-orange color of the cyanidins was markedly decreased by gamma irradiation, the biological activities were relatively unaffected. The biological activities such as 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging activity, inhibition of tyrosinase activity, and inhibition of elastase activity in methanolic extracts were modulated from 50.5% to 70.2%, from 50.9% to 65.8% and from 65.6% to 94.0%, respectively. Surprisingly, the biological activities have the highest activities after 6-8 kGy of gamma irradiation. These results indicate that despite pigment degradation, biological activities were maintained or increased by gamma irradiation. Based on these results, gamma irradiation may be a useful tool to remove the undesirable reddish-orange color present in centipedegrass without any loss of biological activities, thereby promoting its utility in industrial applications such as manufacturing of cosmetic products.