ORAC-Fluorescein Assay To Determine the Oxygen Radical Absorbance Capacity of Resveratrol Complexed in Cyclodextrins

The effect of the complexation of resveratrol with hydroxypropyl-β-cyclodextrins (HP-β-CDs) on the antioxidant capacity of the polyphenol is studied for the first time by means of the oxygen radical absorbance capacity (ORAC) method, using fluorescein (FL) as the fluorescent probe. The method is validated through its linearity, precision, and accuracy for measuring the ORAC of resveratrol in the absence or presence of cyclodextrins (CDs). The complexation of resveratrol in CDs increased the net area under the FL decay curve (net AUC) of resveratrol up to its saturation level, at which the polyphenol showed almost double the antioxidant activity it shows in the absence of CDs. The complexation constant (K c) between resveratrol and HP-β-CDs was calculated by linear regression of the phase solubility diagram (K c = 18048 M−1). The antioxidant activity of resveratrol was dependent on the complexed resveratrol because CDs acts as a controlled dosage reservoir that protects resveratrol against rapid oxidation by free radicals. In this way, its antioxidant activity is prolonged and only reaches its maximum when all the resveratrol is complexed.