Polyphenolic content and comparative antioxidant capacity of flavoured black teas ANNA PE ˛ KAL, PAULINA DRO ´ Z ˙ DZ ˙ , MAGDALENA BIESAGA, & KRYSTYNA PYRZYNSKA Department of Chemistry, University of Warsaw, Warsaw, Poland 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. Keywords: black flavoured teas, polyphenols, antioxidant capacity, FC assay, CUPRAC Introduction Tea infusions, consumed by two-thirds of the world’s population, are obtained from the leaves of one kind of plant named Camellia sinensis. Tea leaves are primarily manufactured as green, black or oolong, with black tea representing approximately 80% of tea products consumed. They differ in appearance, organoleptic taste, chemical content as well as flavour due to their respective oxidation process. The oxidation step of processing converts monomeric phenolic (mainly catechins) into dimeric/oligomeric compounds, such as theaflavins and thearubigins, which are responsible for the characteristic aroma and colour of black tea. In recent years, tea is extensively investigated mainly regarding its influence on human health (Sharangi 2009). The regular intake of tea is associated with an improved antioxidant status in vivo that may contrib- ute to lowering the risk of coronary heart disease, atherosclerosis, reduced mutagenicity and inflam- mation (Kris-Etherton and Keen 2002; Widlansky et al. 2005). Flavonoids and polyphenolic acids are the most abundant compounds in tea leaves and extracts and they are primarily responsible for the beneficial healthful properties of tea (Khan and Mykhtar 2007). The antioxidative properties of flavonoids are manifested particularly by their abilities to inhibit free radical generation, scavenge free radicals and chelate transition metal ions, mainly iron and copper, which are catalysts of free radical reactions (Wang et al. 2000; Heo et al. 2007). They also prevent free radical generation by inhibiting the activity of existing enzymes or by increasing the activity of enzymes with antioxidative properties, probably on the way of induction of protein molecule biosynthesis (Spencer et al. 2009). Because of the great number of different com- pounds with antioxidative properties in a certain product, it is more useful to determine the total antioxidative activity than the individual antioxidant contents (Prior et al. 2005; Karadag et al. 2009; Finley et al. 2011). Moreover, the cooperation among the different antioxidants provides greater protection against reactive oxygen species than any compound alone. The antioxidant capacity of natural products, ISSN 0963-7486 print/ISSN 1465-3478 online q 2012 Informa UK, Ltd. DOI: 10.3109/09637486.2011.653552 Correspondence: Krystyna Pyrzynska, Department of Chemistry, Universityof Warsaw, Pasteura 1, 02-093 Warsaw, Poland. Tel: ( þ 4822) 8220211. Fax: ( þ 4822) 8223532. E-mail: kryspyrz@chem.uw.edu.pl International Journal of Food Sciences and Nutrition, September 2012; 63(6): 742–748