Different extracts and standard (1 mg/mL) in 1 mL of distilled water was mixed with phosphate buffer (2.5 mL, 0.2 mol/L, pH 6.6) and potassium ferricyanide (2.5 mL, 1% w/v) was added to the mixture, which was then centrifuged for 10 min at 3 000 r/ min.