DPPH decolorization was measured after the reaction of sample with the free stable radical DPPH' according to Molyneux (2004). Fresh methanolic solution (2.5 ml) DPPH' were transferred into plastic cuvettes, 10 mm in length,and absobance at a time t0 ranged between 0.200 and 1.000depending no the nature of the sample assayed. Then 5 µl of the sample were added and,after stirring with a hand stirrer in cuvettes, the reaction mixture was left to stand for 5 min. The absorbance was again measured and the percent of inactivation calculated from the decrease of absorbance according to the relationship;
% of inactivation = 100 – [(A15 /A10) x 100] (1)
The calibration curves of ascorbic acid (diluted in 13% ethanol v/v) were made for each DPPH absorbance at t0 (one of the calibration curves, e.g. Fig 1).