Antioxidant Capacity Determination by DPPH

The methodology reported by Erpel et al. (2021) [17 (link)] was followed with some modifications. First, a 39.4 mg/L DPPH in a methanol solution was prepared and stored at 4 °C until use. Subsequently, five methanolic dilutions of the juice samples at different concentrations were prepared. Aliquots of 0.1 mL of each diluted sample were taken, and each was mixed with 3.9 mL of the DPPH solution. The samples were homogenized with a vortex shaker at medium speed and left to rest for 30 min at room temperature in dark conditions. Then, the absorbance of each sample was measured at 517 nm in a Genesys 150 UV–Vis spectrophotometer (Thermo Fisher Scientific, Waltham, MA, USA). The results were expressed in IC50 of mg gallic acid equivalents (GAE) per mL of juice, and the percentage of inhibition of DPPH radicals was calculated according to
$$\mathrm{\%}Inhibition=\left(1-\frac{Ab{s}_{blank}}{Ab{s}_{sample}}\right)·100$$
A 3.9 mL pure methanol sample was used as a blank, and 3.9 mL of the methanolic DPPH solution was used as a negative control.