Objective Chemicals related to the bitter taste of brewed selenium-rich Ziyang tea were identified for improving the drink palatability.

Method An analytical method applying HPLC was established to simultaneously detect 7 key bitter-taste compounds, namely gallic acid, EGC, caffeine, EC, EGCG, rutin, and ECG, in dried tea leaves and brewed tea of 5 selenium-rich Ziyang tea samples on the market.

Result The optimized HPLC methodology used the GL Sciences InertSustain C₁₈ (250×4.6 mm, 5 μm) column for the stationary phase to elute samples with 50 mmol·L⁻¹ potassiumdihydrogen phosphate solution and acetonitrile at a flow rate of 1.0 mL·min⁻¹ and the column temperature of 35 ℃ to obtain chromatograms at the wavelength of 278 nm. The method was validated with determination coefficients exceeding 0.999 on all 7 target compounds within their respective linear ranges. The assay met the analytical requirements with a detection limit of 10-50 mg·kg⁻¹, a quantification limit of 20-100 mg·kg⁻¹, a spike recover rate of 89.5%-95.6%, and a relative standard deviation of 0.1%-3.3%. The analysis on the 5 specimens showed that the ester-type catechins EGCG and ECG to be the predominant bitter substances, accounting for over 70% of the total. The contents of the 7 bitter compounds were EGCG > ECG > EGC > caffeine > EC > rutin > gallic acid. And there were significant variations in ECG and EGCG between samples, indicating substantial heterogeneity among the 5 samples of the same product category.

Conclusion The HPLC assay adequately differentiated the bitter chemicals in the 5 selenium-rich Ziyang tea products on the market. Hot water steeping effectively extracted EGC, caffeine, EC, and rutin from the tea, as the contents in the dried leaves and brewed teas were basically identical. On the other hand, EGCG and ECG were extracted less than 50% of what was contained in the dried tea leaves. As a result, the low solubility rendered weak transfer of these precursors into umami and sweet aftertaste in the brewed tea.