ABTS Assay

The ABTS radical was prepared by mixing in equimolar amounts ABTS (Sigma-Aldrich Chemie GmbH, Darmstadt, Germany) (2,2-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid)) (7 mM in distilled water) and potassium persulphate (2.45 mM in water), which were then left for 16 h in the dark. Prior to the experiment, 2 mL of the solution was mixed with 60 mL methanol (Merck KGaA, Darmstadt, Germany) to obtain a final adsorption of 1.0 ÷ 1.1 at 734 nm by a VIS spectrophotometer Camspec M107 (Spectronic-Camspec Ltd., Leeds, the United Kingdom). For the analysis, 0.15 mL of the studied sample was mixed with 2.85 mL of freshly made ABTS radical solution. The reaction mixture was incubated in the dark for 15 min at 37 ◦C. The adsorption reduction was determined spectrophotometrically at a wavelength of 734 nm [20].
