3.5.3. Ferric Reducing Antioxidant Power (FRAP) Assay

In this study, FRAP assays were performed according to the described method [55]. The antioxidants could restore ferric tripyridyl triazine (Fe³⁺-TPTZ) to blue Fe²⁺-TPTZ under acidic conditions. A FRAP solution was prepared by mixing acetate buffer (300 mM, pH 3.6), TPTZ (10 mM), and FeCl₃ solution (20 mM) in a ratio of 10:1:1 (v/v/v). A sample solution (0.15 mL) was mixed with the FRAP solution (2.85 mL) and incubated at 37 °C for 30 min. The total antioxidant activity of the samples could be measured by the absorbance of Fe²⁺-TPTZ at 593 nm. The results of the FRAP assay were reported in mM FeSO₄. All measurements were performed in triplicate.