2.2.6. Radical Scavenging Assay

Antioxidant activity was determined on the basis of curcumin ability to act as radical scavengers toward the 2,2-diphenyl-1-picrylhydrazyl free radical, (DPPH•) (Sigma) [23]. Solutions of GEL-02, GEL-05 and GEL-1 were prepared by dissolving the solid samples in MilliQ water/EtOH and thereafter they were diluted, based on their known curcumin contents, in order to get 10 µM, 30 µM and 50 µM of curcumin concentrations. Dilutions of pure curcumin (Merck), 10 µM, 30 µM and 50 µM, were prepared and used as reference samples. For the assay, 6 mL of each solution (samples and references) were added to 0.2 mL of 1mM DPPH• solution in ethanol, previously clarified by centrifugation (10,000 rpm for 10 min). After an incubation for 30 min at room temperature in darkness, absorbance values (A) were spectrophotometrically measured at 517 nm.

The radical scavenging activity (RSA) was determined through the following equation:

where A₀ is the absorbance of the control (containing DPPH• solution without curcumin), and A_x is the absorbance in the presence of curcumin (as reference) or of curcumin-containing samples.