Evaluation of individual phenolic compounds and antioxidant properties of black, green, herbal and fruit tea infusions consumed in Serbia: spectrophotometrical and electrochemical approaches

The aim of this study was evaluation of individual phenolic compounds and antioxidant activity of commercially consumed black, green, fruit and herbal tea infusions in Serbia in order to characterize the quantity and quality of teas. The most abundant compound was gallic acid, followed by caffeic acid, rutin, (+)-catechin and (-)-epicatechin. The main procyanidin was procyanidin B1. The antioxidant activity was measured using five in vitro methods: determination of 1,1-dipheny1-2-picrylhydrazyl radical-scavenging activity (DPPH), 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) radical cation-scavenging activity (ABTS), ferric reducing antioxidant power (FRAP), reduction power (RP) Fe(III) to Fe(II) and cyclic voltammetry (CV). Obtained results of FRAP and of the Fe(III)/Fe(III) method correlated strongly with the total phenolics content (R-2 = 0.92246, R-2 = 0.88084, p lt 0.0001). Antioxidant power of green tea and bearberry tea was considerably higher than that of black tea. Raspberry and cherry showed the highest antioxidant power among fruit tea infusions. Contribution of phenolic compounds to tea antioxidant activity was also quantified in this study. Stepwise linear regression demonstrated that quantification of different phenolic compounds responsible for tea antioxidant activity was dependent on the method used. Gallic acid, caffeic acid (+)-catechin, (-)-epicatechin, (-)-epigallocatechin, procyanidin B1, procyanidin B2 together made up 43.6-99.9% of the antioxidant activity of tea