OBJECTIVETo investigate DPPH radical scavenging activities of 31 flavonoids and phenolic acids and 10 extracts of Chinese materia medica.

METHODThe antioxidant activities of the above samples were evaluated by a DPPH method, the half-wave oxidation potentials (E1/2) of the 31 compounds were determined by an HPLC-CoulArray method, at the same time, phenolic contents of the the total compounds in the 10 extracts of Chinese materia medica were analyzed by Folin-Ciocalteu method.

RESULTThe 31 compounds showed a 50% inhibition of DPPH radical in the concentration range of 6.7-3 500 micromol x L(-1), in which (-) -EGCg demonstrated the strongest activity with the IC50 value of 6.7 micromol x L(-1). The E1/2 of 31 compounds spanned a wide potential range of more than 0.6 V. Myricetin had the lowest E1/2 value (20 mV) whereas apigenin and vitexin-2"-O-rhamnoside had the highest E1/2 value (620 mV). Among the 10 herb extracts, having 82% phenolic acid, tea extract showed the strongest DPPH radical scavenging activity with the IC50 value of 0.011 7 mg x mL(-1) whereas safflower demonstrated the weakest DPPH radical scavenging activity with the IC50 value of 1.250 mg x mL(-1), in which only 7% phenolic acids was tested.

CONCLUSIONThe DPPH radical scavenging activities of the 31 compounds were founded to be related to their chemical structures, such as the number and position of hydroxyl groups. And a qualitative relationship was found between DPPH radical scavenging activities and E1/2 values of the 31 compounds, the lower the E1/2 values, the higher the DPPH radical scavenging activities. A quantitative relationship was obtained to describe the DPPH radical scavenging activity of the herb extracts: Y = 7.779X(-0.48), r = 0.929 5, where Y stands for the concentration for 50% inhibition of DPPH radical, and X stands for the concentration of total phenolic compaunds, namely the extracts with higher content of flavonoids and phenolic acid exhibited the stronger DPPH radical scavenging activity.