DPPH is a stable free-radical molecule widely used assay to
measure the free radical scavenging capacity of plant extracts.
Assay was initiated by adding 200 ll of 0.004% DPPH
methanolic solution into 96-well plate, followed by addition
of 20 ll of H. rhamnoides extract, or solvent or the blank.
The mixture was incubated at 30 C for 1 h and the absorbance
was measured at 515 nm in a microplate reader (Multiskan,
Thermo Scientific) (Kim et al., 2002; Bertrand et al., 2005).
The percentage of inhibition was calculated as:
Inhibition % ¼ 100 100ðAs AoÞ
where Ao is the absorbance of the blank and As is the absorbance
of the sample at 515 nm.