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Abstract
The content of selected flavonoids and phenolic acids of 12 commercial flavoured black tea infusions was determined by high-performance liquid chromatography with tandem mass spectrometry in the negative electrospray ionization mode. Assays for the evaluation of their antioxidant capacity were carried out by cupric ion reducing antioxidant capacity, Folin–Ciocalteu assay, cyclic voltammetry and potentiometry. Flavonoids were predominantly present as glycosides in the studied infusions. Only quercetin as a free aglycone was found at trace levels. Notable amount of naringin and hesperidin was determined in teas with citrus aromas or fruits. These compounds were not found in premium black tea. Two principal groups of the studied teas were found using cluster analysis in relation to the values of their antioxidant activities.