Abstract: The effect of Mg2+ in brewing water on the taste quality and chemical ingredients of black tea infusion was investigated. The underlying mechanism was inferred from the interaction among the main taste substances of black tea infusion in the presence of Mg2+. The results showed that the quality of tea infusion with high Mg2+ concentration (≥ 16 mg/L) was fairly poor. As the concentration of Mg2+ increased, the umami taste, sweetness and bitterness of tea infusion decreased, while the astringency significantly increased. The contents of tea polyphenols, catechins, amino acids and caffeine, as well as Al3+, B3+, K+, Na+ and S6+ in tea infusion showed a downward trend, partially accounting for the decrease in the bitterness and umami taste of tea infusion. Furthermore, we found that Mg2+ not only enhanced the astringency of epiggallocatechin gallate (EGCG), caffeine and sodium glutamate solutions, but also weakened the bitterness of EGCG and caffeine solutions, the umami taste of sodium glutamate solution and the sweetness of sucrose solution, indicating a significant effect of Mg2+ on the taste components. With increasing concentration of Mg2+ in brewing water, the turbidity of EGCG-protein mixture solution increased significantly, which confirmed the conclusion that Mg2+ can strengthen the astringency intensity of tea infusion. The results of this study suggested that water that contain relatively low concentration of Mg2+ (≤ 4 mg/L) be used for brewing of black tea in daily life.

Key words: Mg2+; black tea infusion; taste quality; taste compounds