2.4 Evaluation of total antioxidant capacity (TAC) by Phosphomolybdenum method
The total antioxidant capacity of the methanol extract was evaluated by the
phosphomolybdenum method according to the procedure described by Prieto et al.
(1999[19]). The assay is based on the reduction of Mo (VI) to Mo (V) by the extract and
subsequent formation of green phosphate/Mo (V) complex at acid ρH. A 0.3 ml extract was
combined with 3 ml of reagent solution (0.6M sulfuric acid, 28 mM sodium phosphate and 4
mM ammonium molybdate). The absorbance of the reaction mixture was measured at 695 nm
using a spectrophotometer (Jenway 6025) against blank after cooling to room temperature.
Methanol (0.3 ml) in the place of extract was used as the blank. The antioxidant activity is
expressed as the number of gram equivalent of ascorbic acid. The calibration curve was
prepared by mixing ascorbic (1000, 500, 250, 125, 62.5 and 31.25 µg/ml) with methanol.