2.8. Ferric Reducing Antioxidant Power (FRAP) Assay

A FRAP assay was performed following a previously reported method with modifications [24]. Briefly, 190 µL of freshly prepared FRAP working solution, which was composed of 300 mM of acetate buffer (pH 3.6), 20 mM of FeCl₃·6H₂O solution, and 10 mM of TPTZ solution at a ratio of 10:1:1 (v/v/v), was pre-warmed at 37 °C, and 10 µL of the sample solutions of various concentrations were mixed in a 96-well plate and incubated for 10 min at 37 °C. Then, the absorbance of the mixture was monitored by a microplate reader at 593 nm. A standard curve was established by FeSO₄·7H₂O, and the total antioxidant capacities of these tested compounds were calculated accordingly and expressed in terms of the FeSO₄ values. Vitamin C was used as a positive control, and all of the tests were repeated three times independently.