2.6. Ferric Reducing Antioxidant Power (FRAP), DPPH Free Radical Scavenging, and Antioxidant Capacity

FRAP was carried out according to Benzie and Strain (1996) [38], where extract was mixed with FRAP reagent (2.7 mL) and topped of to 3 mL with distilled water. The mixture was allowed to react in the dark for 30 min at 37 °C. The absorbance of the solution was recorded at 593 nm, and the results are expressed in terms of mM FeSO₄ g⁻¹ or mL⁻¹ of the sample, whereas DPPH free radical scavenging activity of pomelo fruit was determined as per the method of Blois (1958) [39]. In brief, the extracts (0.5 mL) were mixed with 3 mL of DPPH solution in methanol (0.1 mM). The prepared mixture was allowed to react in the dark at 37 °C for 30 min, and absorbance was measured at 517 nm. Ascorbic acid was used as a positive control.

where A_c = Absorbance of control; A_s = Absorbance of sample

The antioxidant capacity by the phosphomolybdenum method of pomelo fruit was evaluated according to the method described by Jayaprakasha et al. (2002) [40]. Briefly, extract (100 μL) was mixed with 1 mL of freshly prepared reagent solution (0.6 mol L⁻¹ sulfuric acid, 28 mM L⁻¹ sodium phosphate, and 4 mmol L⁻¹ ammonium molybdate). Extract solution (80% methanol and 20% water) was used as blank. The mixture was vortexed and screw capped. The tubes were incubated for 90 min at 95 °C in a boiling water bath. The tubes were allowed to cool at room temperature and the developed green color of the solution was read at 695 nm against a blank. Total antioxidant capacities of the pomelo fruit extract were expressed in terms of ascorbic acid equivalents (mM g⁻¹ or mL⁻¹ of sample).