3.10. Oxygen Radical Absorbance Capacity (ORAC) Assay

The ORAC method is widely used for assessing antioxidant capacity in biological samples and food [53]. The assay consists of measuring the decreased fluorescence of a protein as a result of loss of its conformation when it suffers oxidative damage caused by a source of peroxyl radicals; hence, the method is capable of measuring the antioxidant ability of the sample to protect the protein (fluorescein) from oxidative damage [54]. Currently, the assay is able to measure the hydrophilic and lipophilic antioxidants through the use of different solvents with different polarities as acetone/water/acid acetic in a gradient [55].

ORAC assays were performed for samples of AOE. ORAC values were determined using the method described by [56], which in turn is based on the method of [57] with a few modifications. The area under the fluorescence decomposition curve (AUC) was used in the calculations through a linear regression equation in trolox standards. The net area under the curve was obtained by subtracting the area below the curve for the blank values of the sample curves and standards. Finally, the ORAC value was expressed in µmol of trolox equivalents per gram (µmol of TE/g).