FRAP was assayed according to the method of Benzie and Strain (1996) as described by Maqsood and Benjakul (2010). The stock solution included 300 mM acetate buffer (pH 3.6), 10 mM TPTZ solution in 40 mM HCl, and 20 mM FeCl3•
6H2O solution. A working solution was prepared freshly by mixing 25 mL of acetate buffer, 2.5 mL of TPTZ solution and 2.5 mL of FeCl3•6H2O solution. The mixture was incubated at 37 °C for 30 min and was referred to as FRAP solution. Sample (0.2 mg/mL; 150 μL) was mixed with 2850 μL of FRAP solution and kept at room temperature (26–28 °C) for 30 min in the dark. The ferrous tripyridyltriazine complex (colored product) was measured by reading the absorbance at 593 nm using a spectrophotometer. The control was prepared in the same manner, except that distilled water was used instead of the sample. The standard curve was prepared using tannic acid ranging from 0 to 100 ppm. The activity was expressed as mg of tannic acid equivalents (TA)/g sample.