Abstract: Commelina communis L. (CCL) was extracted with methanol-chloroform (2:1), and then the extract was partitioned with petroleum ether, EtOAc and BuOH successively. Antioxidant activities (AA) of different end extracts were evaluated by three different methods, namely, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay, deoxyribose assay and potassium ferricyanide reduction method, and compared with those of butylated hydroxytoluene (BHT) and gallic acid (GA). The results showed that the ethyl acetate-soluble fraction exhibits the highest AA at four concentration levels (0.4, 2, 10 and 50 μg/ml). It can be further fractionated into six subfractions EAF1～EAF6 by silica gel vacuum liquid chromatography. Among them EAF4 is found to be the most effective subfraction by the three assays, which has stronger AA than BHT at the four concentration levels and greater AA than GA at the concentration of 10μg/ml and 50μg/ml by the DPPH assay. While, by the deoxyribose assay the EAF4 exhibits higher AA than BHT and GA at all of the four concentration levels and by the potassium ferricyanide reduction methods it exhibits higher AA than BHT and lower AA than GA.

Key words: natural antioxidant, Commelina communis L., DPPH, hydroxyl radical, reducing power