3.6. DPPH Radical Scavenging Assay

The DPPH free radical scavenging activity was determined by Yang’s method, with some modifications [38]. Each sample (PSPs, PSPs-EH20 and PSPs-EH80), at a different concentration (from 0 to 2.5 mg/mL) in 2 mL distilled water was mixed with 2 mL 1 mM DPPH solution (dissolved in methanol). The mixture was shaken vigorously and then left to stand in the dark for 30 min. The absorbance of the control sample was accomplished by replacing the test sample with methanol. The DPPH radical scavenging activity was determined by measuring the absorbance at 517 nm using a spectrophotometer (Hitachi U-3010). A control test was performed with distilled water, but without a test sample; the solution without DPPH added was used as a control. The DPPH radical scavenging activity was calculated as follows: