Ferric reducing antioxidant power (FRAP) assay

In this reaction, the color changed from yellow to green, based on the reducing capacity of the sample. Fe³⁺/ferricyanide complex was reduced to the ferrous form by reductants in the solution. Thus, Fe²⁺ can be traced as the reducing power index by measuring the absorbance [48]. The FRAP study was conducted with modifications [49,50]. The FRAP reagent was prepared daily by incubating a mixture of 10 mL of ferric trichloride hexahydrate (20 mM) solution, 10 mL of TPTZ (10 mM in 40 mM hydrochloric acid) solution and 100 mL of 0.3 M acetate buffer (pH 3.6) at 37°C. For each analysis, 400 μL of sample (0.1 mM) were mixed with 3 mL of FRAP solution. The increase in the absorbance at 593 nm was monitored at 15 s intervals over 30 min at 37°C. The FRAP profiles were displayed as micromoles of Trolox equivalent per gram of dry samples (μmol equiv. Trolox g⁻¹). All tests were conducted in triplicate.