Determination of the effects of adding milk and sugar on the antioxidant capacity of oolong tea by chemical and cell culture-based antioxidant assays

The effect of sugars and/or milk on the antioxidant capacity of Oolong tea was evaluated using 2,2′-azino-bis 3-ethylbenzothiazoline-6-sulfonic acid diammonium salt (ABTS), ferrous ion-chelating (FIC) and cellular antioxidant activity (CAA) assays. The addition of sugar did not alter the antioxidant capacity of tea (p < 0.05), however with the addition of sweetener an 18% and 14% increase was observed using ABTS and FIC assays respectively. In contrast, using the CAA method, the sweetener decreased the tea antioxidant capacity by 8%. Milks and milks and sugars decreased the antioxidant capacity of tea by 30% and 45% respectively determined by ABTS and CAA assays, with an opposite result using the FIC method. The chemical and cellular based methods showed poorly correlated values.