*3.1.3. Ferric Ion Reducing Antioxidant Power (FRAP) assay*

Analysis of antioxidant activity by performing a FRAP assay was proposed by Benzie and Strain [23]. It involves colorimetric determination of the reaction mixture in which the oxidants contained in the sample reduce Fe3+ ions to Fe2+. At low pH, Fe(III)-TPTZ (ferric-tripyridltria‐ zine) complex is reduced to the ferrous (Fe2+) form and intense blue colour at 593 nm can be observed. The FRAP reagent is prepared by mixing 2.5 ml of TPTZ (2,4,6-tris (1-pyridyl)-5 triazine) solution (10 mM in 40mM HCl), 25 ml acetate buffer, pH 3.6, and 2.5 ml FeCl3•H2O (20 mM). The colour of Fe(II)(TPTZ)2 which appears in the solution is measured colorimetri‐ cally after incubation at 37o C. The measurement results are compared to those of a blank sample, which contains deionised water instead of the analysed sample. The duration of the assay differs from one study to another: 4 min [23, 24], 10 min [25] to 15 min [26]. The analysis results are converted and expressed with reference to a standard substance, which can be ascorbic acid [26], FeSO4 [23, 25], Trolox [27,18].
