Study on antioxidant and inhibition of α-glucosidase activities in vitro of different solvent extracts from onion skin(Allium cepa L.)

This study investigated extraction effect of different solvents on total polyphenols, total flavonoids and quercetin and the antioxidant and inhibition of α-glucosidase activities of extracts from onion skin (Allium cepa L.). The active ingredients of purple onion skin as raw material were extracted with water, 40%~100% ethanol solution, ethyl acetate and petroleum ether respectively. The effects of different solvents on total polyphenols, total flavonoids and quercetin were analyzed. The total reducing power, scavenging DPPH·, ABTS⁺·, O₂^-·and inhibition of α-glucosidase activities of different solvent extracts, which were compared with contents of total polyphenols, total flavonoids and quercetin were determined. Results showed that the highest extraction rate and contents or purity of total phenols, flavonoids and quercetin were determined in 60% ethanol extracts, which were respectively up to 5.5%, 9.87%, 3.25% and (33.12%±0.39%), (59.44%±0.38%), (19.56%±0.14%). The high reducing power, scavenging activities on DPPH·, ABTS⁺·, O₂^-·and inhibition of α-glucosidase activities were determined in 40% and 60% ethanol extracts. The correlation between total flavonoids and quercetin contents in onion skin extracts and antioxidant and inhibition of α-glucosidase activities all reached significant or extremely significant level. Actually, the correlation between quercetin contents in extracts and scavenging activities, inhibition of α-glucosidase activities reached the highest level.