Assessments of antioxidant effect of black tea extract and its rationals by erythrocyte haemolysis assay, plasma oxidation assay and cellular antioxidant activity (CAA) assay

• Black tea extract (BTE) played an antioxidant role against oxidative stress.
• The antioxidant rationals included suppressing the formation of ROS.
• The antioxidant rationals included inhibiting copper-induced lipid peroxidation.
• The antioxidant rationals included suppressing AAPH-generated peroxyl radicals.
• TP, especially thearubigins (TR) and theabrownins (TB) were the main contributors.

Fresh tea leaves were processed into black tea and cell-based assays (erythrocyte haemolysis assay and cellular antioxidant activity (CAA) assay) and plasma oxidation assay were used to study the total antioxidant activity of black tea extract (BTE). The results indicated that BTE showed a dose-dependent protection against the 2, 2'-Azobis (2-amidinopropane) (AAPH)-induced erythrocytes oxidative haemolysis and copper-induced plasma oxidation. The CAA value of BTE was 16.4 µmol quercetin equivalents (QE)/100 mg solid. The antioxidant rational of BTE in biological systems included suppressing the formation of ROS by preserving the activities of the antioxidant enzymes as well as inhibiting the formation of thiobarbituric acid reactive substances (TBARS), inhibiting the copper-induced lipid peroxidation of LDL and HDL, suppressing AAPH-generated peroxyl radicals by preventing the oxidation of DCFH and membrane lipid and the decrease of DCF formation. Tea polyphenols, especially thearubigins and theabrownins, were the main contributors to antioxidant activity of BTE.