This assay detected scavenging of free radicals by the tested
compound through the scavenging activity of the stable DPPH
free radical. This assay was performed using a previously
described method (Sumner et al., 1981) with slight modifications.
Briefly, 2 mL sample solutions with different concentrations
were mixed with 2 mL DPPH solution (0.2 mg/L) in
95% ethanol, reacted for 30 min, and then the absorbance of
the sample was measured at 517 nm by a spectrophotometer.
The result of antiradical activity was expressed as a percentage
clearance rate calculated by the following equation:
Clearance rateð%Þ ¼ ½ðA0 A1Þ=A0 100%;
where A0 was the absorbance of control and A1 was the absorbance
of the protein, respectively.