DPPH radical scavenging activity

DPPH assay has been widely used for the determination of antioxidant activity of pure antioxidant compounds as well as of different plant extracts, a lower IC₅₀ representing stronger antioxidant capacity²⁴. IC₅₀ obtained by interpolation from linear regression analysis is the effective sample concentration at which DPPH radicals is scavenged by 50%. A slightly modified DPPH method was used to determine the radical scavenging property of P. fruticosa leaves⁵⁸. Amounts of 2 mL of the tested samples (1–100 μg/mL) and the positive controls (rutin, 1–70 μg/mL) were mixed with 2.0 mL of 0.1 mol/L DPPH in methanol. The mixture was vortexed thoroughly and allowed to stand in the dark for 30 min. The absorbance was measured at 517 nm spectrophotometrically against a blank. All measurements were performed in triplicate. DPPH free radical scavenging activity (SA) can be expressed with the following equation (6):

where A_i: absorbance of tested samples (2 mL) mixed with DPPH (2 mL); A_j: absorbance of tested samples (2 mL) mixed with methanol (2 mL); A₀: absorbance of methanol (2 mL) mixed with DPPH (2 mL).