The ABTS+ cation radical method was used to determine the antioxidant activity of the extracts. A 2 mm ABTS+ stock solution containing 3.5 mM potassium sulfate (VI) was prepared by diluting the stock solution eight times in methanol and incubating it overnight at room temperature in the dark to allow radical stabilization. An Acquity UPLC liquid chromatography system (Waters, Milford, MA, USA) with a Waters Acquity PDA detector (Waters, Milford, MA, USA) and an Acquity UPLC® BEH C18 column (150 mm × 2.1 mm, particle size 1.9 μm) (Waters, Dublin, Ireland) were used. The gradient started with A—0.1% aqueous formic acid solution in acetonitrile and B—0.1% aqueous formic acid (10:90, %, v/v to 40:60, %, v/v) for 15 min. The chromatogram was recorded at a 280 nm wavelength. The injection volume of the sample was 10 µL, and the flow rate was 0.4 mL/min. After running through the column, the UPLC elution returned to baseline. The sample was then re-injected with ABTS+. This time, the chromatogram was recorded at a 734 nm wavelength. The antioxidant activity was calculated from the difference in peak areas of both chromatograms and compared with the standard curve for TROLOX. Each commercial compound standard was obtained from Sigma (St. Louis, MO, USA). The obtained results were converted into 1 g of extract [27 (link),28 (link),29 (link)].
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