2.7. Antioxidant Assays DPPH and ABTS

The antioxidant capacity was evaluated in the 27 orange by-products extracts by two different methods. The first one was the developed by Re at al. [22] in which the monocation ABTS^•+ is generated by oxidation of the ABTS with potassium persulfate in the dark at room temperature for 12–24 h. For each extract, it was added 1 mL of this ABTS solution to 0.01 mL of extract and it was measured the detriment of absorbance during 10 min at 734 nm. The results were compared with a standard curve of Trolox (1, 10, 20, 50, 80, 100, 150, 200 ppm). DPPH radical scavenging activity was assayed with a method proposed by several authors [23,24]. Then, 100 µL of each extract was added of 2.9 mL of DPPH, and after rapid stirring, the bleaching power of the extract was observed in a time interval from 0 to 30 min at 517 nm. The results were compared with a standard curve of Trolox in methanol/water (4:1, v/v) (1, 10, 20, 50, 80, 100, 150, 200 ppm). Results for both assays are expressed as mg Trolox equivalents (TE)/g d.w.