This was determined according to the method of Oyaizu (1986).
The extract or standard (100 µg/ml) was mixed with phosphate
buffer and potassium ferricyanide. The mixture was incubated at
50˚C for 20 min. Tricloroacetic acid (10%, 2.5 ml) was added to the
mixture. A portion of the resulting mixture was mixed with FeCl3
(0.1%, 0.5 ml) and the absorbance was measured at 700 nm in a
spectrophotometer. Higher absorbance of the reaction mixture
indicates higher reductive potential.