Dual effect of milk on the antioxidant capacity of green, Darjeeling, and English breakfast teas

Past studies present contradictory results regarding the effect of milk on the antioxidant capacities of teas, possibly because of the different methods used. Here, we re-address the question by using three complementary assays, ABTS' free radical scavenging, voltammetry, and lipid peroxidation inhibition, to estimate how milk affects the antioxidant capacities of green, Darjeeling, and English breakfast teas. We observed that milk decreased the antioxidant capacities of Darjeeling (-8.3%), green (-6.0%), and English breakfast (-19.6%) teas, estimated with the ABTS' method. These inhibitions were four times larger using voltammetry. In contrast, milk enhanced the chain-breaking antioxidant capacity of teas in the lipid peroxidation method by 19%, 12%, and 10%, for green, English breakfast, and Darjeeling teas, respectively. Therefore, milk can have dual effects on the tea antioxidant capacity, an inhibitory effect for reactions occurring in solution or at a solid-liquid interface and an enhancing effect for those in oil-in-water emulsion. The mechanisms responsible for these different milk-tea interactions are discussed. (C) 2010 Elsevier Ltd. All rights reserved.