The effect of ascorbic acid on total antioxidant activity of black and green teas
Author: Dorota Majchrzak and Sabine Mitter and Ibrahim Elmadfa
The beneficial effects of green and black tea are generally attributed to the antioxidant activity of their phenolic compounds. Tea is commonly used with milk or lemon. Milk proteins might complex with tea polyphenols and reduce their antioxidant activity. Lemon contains vitamin C (ascorbic acid) which has antioxidative properties and can positively influence the antioxidant potential of tea. The present study aimed to compare, in vitro, the antioxidant activities of different commercially available types of tea, prepared by commonly used domestic methods and to evaluate the possible effects of different doses (5–40 mg/100 ml) of vitamin C (ascorbic acid) on the total antioxidant capacity (TAC) of tea. The antioxidant activity of tea extracts was determined by the photometric method, according to Rice-Evans and Miller [Methods Enzymol. 234 (1994) 279], measuring the formation of the radical cation ABTS. The values of antioxidant activity of teas prepared in the same way as when consumed were in similar ranges, from 13.3 to 21.6 mmol TE (TE = Trolox equivalents) in green tea and 10.4–17.6 mmol TE in black tea. The experiment in which ascorbic acid was added to teas showed that TAC in black tea extracts increased in a linear manner between 5 and 20 mg ascorbic acid/100 ml tea solution (r=0.984; p<0.01) and in green tea extracts up to 30 mg ascorbic acid/100 ml tea solution (r=0.959; p<0.01).