The hydrogen atoms or electrons donation ability of the plant
extracts and some pure compounds were measured from the
bleaching of a purple-coloured methanol solution of DPPH[13].
Briefly, 1 mL of a 0.01 mmol/L solution of DPPH radical in methanol
was added to 4 mL of the extract at different concentrations. The
absorbance of the resulting solution was measured after 30 min
in dark at 514 nm with a spectrophotometer (Selecta, E.U.). The
percentage inhibition of activity was calculated as:
%Inhibition=
Ablank-Asample
Ablank
×100
BHT and ascorbic acid was used as positive control and the
concentration providing 50% inhibition (IC50) was calculated
from the graph of inhibition percentage plotted against the extract
concentration.