2.7. Free radical scavenging activity
Radical scavenging activity of the seven extracts
was measured using the stable radical DPPH . The
procedure followed was according to Brand-Williams,
Cuvelier, and Berset (1995) with some variations.
For each extract, different concentrations were tested.
At least 5 dilutions of each extract were prepared in
methanol using a 10 ml volumetric flask (methanol
for the control). Concentrations ranged from 48 to
1.51 mg/ml for less active extracts and from 10 to
0.33 mg/ml for more active ones. An aliquot of methanol (0.1 ml) solution containing different concentrations of orange peel extracts was added to 3.9 ml of
DPPH (104 M). Absorbance was measured at 515
nm until the reaction reached a plateau (each measurement repeated twice). After preliminary experiments,
the plateau was fixed at 4 h for all the extracts due
to the slow kinetics of certain extracts. The absorbance
of the DPPH solution, was measured daily. The
DPPH concentration in the reaction medium was calculated from the following calibration curve, determined by linear regression: