Antioxidant capacity assays

The antioxidant capacity assay was determined by DPPH, ABTS and FRAP methods. The DPPH was performed according to the method descripted previously (Barreca et al. 2011). For each sample (50 μL), 63 μM of DPPH was added, and the a final volume was adjusted to 4.0 mL with methanol. After 25 min, the absorbance was detected at wavelength of 517 nm. The inhibition percentage of radical scavenging capacity was the DPPH value.

ABTS values were measured according to the previous method (Barreca et al. 2011). 5 mL aqueous ABTS solution (7 mM) was added to 88 µL of 140 mM of a potassium per sulfate solution. The mixture was kept in dark at 29 °C for 14 h before being used. The decrease of absorbance was measured in 6 min at 734 nm.

The FRAP assay was conducted by the previous method described (Jang et al. 2010). 1.8 mL of FRAP reagent was added to 20 μL of fruit extract and mixed with 1.8 mL deionised water. After 30 min, the absorbance was detected at wavelength of 593 nm. Aqueous solutions of 0–5 mM ferrous sulphate heptahydrate were used for calibration and reducing power was expressed as mM. All absorbance values were determined by using the above spectrophotometer. All tests were run in triplicate. DPPH, FRAP and ABTS were expressed as μM rutin equivalents (TE)/g FW.