4.5.2. Assay for Radical Scavenging with ABTS+

The evaluation of the antioxidant activity of essential oils was examined by applying the ABTS⁺ method [107]. The methodology relies on the percentage inhibition in the peroxidation of this radical, observable at a wavelength of 734 nm, in an alkaline medium as a darkening of a blue-green solution. The stock solution was prepared by adding equal volumes (25 mL) of potassium persulfate solution (2.45 mM) and ABTS⁺ (7.4 mM) ([2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (98%), Alfa Aesar, Karlsruhe, Germany, J65535). The resulting solution was then left in the dark (12 h) at room temperature to react. Following, the solution was diluted by adding 60 mL of methanol to 1 mL of ABTS⁺ solution until an absorbance of 1.1 ± 0.02 units was reached. The essential oil solutions (75 µL) were mixed with 75 µL methanol (Chempur, Piekary, Slavkie, Polonia) and 2850 µL of the ABTS⁺ solution in the dark for 2 h. Afterwards, the absorbance was measured at 734 nm. The standard Trolox [(R)-(+)-6-hydroxy-2,5,7,8-tetramethyl-chromal-2-carboxylic acid (98%), Sigma-Aldrich Chemie GmbH, Steinheim, Switzerland-391913] calibration was used. Results were expressed as µM Trolox equivalents (TE) per mL of sample.