Extraction Characteristics and the Correlation of Bioactive Compounds in Black Tea Considering the Mineral Composition of Brewing Water

This study investigates the effects from mineral composition in the brewing water on the extraction characteristics and correlations of bioactive compounds in black tea. Eight types of water with varying mineral compositions were used to prepare black tea, and the concentrations of key functional compounds—including caffeine, catechins [(+)-gallocatechin (GC), (-)-epigallocatechin (EGC), (+)-catechin (C), (-)-epicatechin (EC), (-)-epigallocatechin gallate (EGCG), (-)-epicatechin gallate (ECG), (-)-catechin 3-gallate (C3G)], and theaflavins [(theaflavin (TF), theaflavin-3-gallate (TF3G), theaflavin-3'-gallate (TF3'G), theaflavin-3,3'-digallate (TF3,3'DG)] —were quantified using HPLC. Correlation analysis between compounds and major mineral ions (Na, Mg, Ca, K, Si, SiO2, SO4²⁻) in the water was conducted using Spearman’s rank correlation. The results revealed significant positive correlations between EGC, C, and caffeine with Mg2+ and Ca2+, indicating that hardness ions may enhance the solubility and stability of water-soluble compounds. In contrast, theaflavin derivatives such as TF3G and TF3,3′ DG showed significant negative correlations with Mg2+ and Ca2+, suggesting potential suppression or precipitation effects under high ionic conditions. Additionally, SO4²⁻ showed a positive correlation with GC, implying its selective role in extraction facilitation. These findings highlight the critical role of water mineral composition in modulating the extraction behavior of functional compounds in black tea and suggest that water design is a strategic variable in optimizing tea quality and developing functional tea beverages.