Abstract: In this study,the methanol extract of Pteroxygonum giraldii root and its ethyl acetate fraction,butanol fraction and water fraction were used to investigate the DPPH radicals scavenging activity,reducing power,metal chelating and angiotensin converting enzyme (ACE) inhibition activity.The total phenol content of four extracts were 147.97,228.31,162.99,168.16 mg gallic acid/g,the total flavonoid content of four extracts were 19.45,21.57,13.89,14.80 mg quercetin/g respectively,the four extract exhibited strong DPPH free radical scavenging activity with the EC₅₀ of 52.37,11.43,46.45,50.32 μg/mL respectively.The reducing power of all samples showed a dose-dependent manner.The reducing power was even stronger than the standard BHA at concentration level of 100 μg/mL.The ethyl acetate fraction showed 37.79% metal chelating ability at 100 μg/mL.The methanol extract and ethyl acetate fraction exhibited the 39.45% and 39.76% ACE inhibition activity at 100 μg/mL.These results showed that the antioxidant activities of P.giraldii extract were correlated with its total phenolic and flavonoid contents.In addition,there was a positive correlation between the antioxidant activity and ACE inhibition activity.

Key words: Pteroxygonum giraldii, total phenol, flavonoids, antioxidant activity, ACE