Objective: To investigate DPPH radical scavenging activities of 31 flavonoids and phenolic acids and 10 extracts of Chinese materia medica.
Method: The 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.
Result: The 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.
Conclusion: The 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.