An aliquot of each antioxidant (50 μl) was added to 2 ml of DPPH radical methanolic solution (3.6 × 10−5M), shaken vigorously in a vortex and left to stand
in the dark at room temperature. The absorbance was measured at
515 nm in a spectrophotometer, after 16 min at room temperature. All
determinations were made in triplicate. The decrease in absorbance
was converted to percentage of DPPH inhibition (IP), according to the
following equation: