Abstract: Chromogenic reaction level of catechins from the green tea and the black tea with hydrochloric acid(sulfuric acid-vanillin)-vanillin was determined in this paper. By determining and comparing the reaction coefficient, accuracy and precision, the color reaction ability of catechins reacted with acid vanillin was evaluated. The results showed that the reaction system was sensitive to catechins with a high linear correlation(R_HA²=0.997 6±0.001 4, R_SA²=0.997 8±0.001 8). It was also seen that the chromogenic reaction coefficients from both systems were less than the Roberts coefficient (145.68) obtained from the empirical formula for calculating catechins aggregates. The recoveries from both system were more than 94.22% and all the variation coefficient of precision were less than 0.08%. This showed that both systems could determinate tea catechins aggregates. The chromogenic capability of tea catechins from different sources with acid-Vanillin was very different from each other (F=37.434>F_0.01(1,5)=6.61). This results showed that two kinds of reaction systems could objectively reflect tea catechins aggregates. However, both recoveries and variation coefficient from the empirical formula were instable and the total catechins aggregates was higher than the reality.

Key words: tea catechins, colorimetric determination, acid-vanillin, chromogenic reaction ability