4.4.2. ABTS Radical Scavenging Assay

The procedure applied to evaluate the ABTS radical scavenging activity was described previously by Nowak et al., with modifications [38]. Shortly, a 7-mM solution of ABTS (2,2′-azino-bis(3-ethylbenzothiazoline-6sulfonic acid)) in a 2.45-mM aqueous solution of potassium persulfate was used as a stock solution. After dissolving the components, the solution was incubated for 24 h in the dark at room temperature, then diluted with 50% (v/v) methanol to obtain a working solution of absorbance of 1.00 ± 0.02 at 734 nm. The antioxidant activity was measured as follows: 2.5 mL of working ABTS solution and 0.25 mL of a studied sample at the concentrations range of 10–1000 µg/mL were introduced into the spectrophotometric cuvette. As with the DPPH method, kinetics of the absorbance changes was done (see Section 4.4.1). The ABTS scavenging was calculated from the equation:

where:

A_s—absorbance of the tested sample;

A_c—absorbance of the control sample.

Measurements were carried out in triplicate for each extract sample.