In Vitro Stability and Pharmacokinetic Evaluation of 12 Compounds in Qingzhuan Dark Tea in Rat Models

Objective This study aims to systematically evaluate the in vitro stability and pharmacokinetic behavior of representative polyphenols in Qingzhuan dark tea (QDT) and to explore the relationship between physicochemical stability and systemic exposure. Methods Twelve representative polyphenols, including eight catechins and four theaflavins, were evaluated using a three‐factor, three‐level L 9 orthogonal design to investigate the effects of pH, temperature, and time on stability. Based on stability and plasma detectability, seven catechins were further investigated in male Sprague–Dawley rats following oral administration of QDT extract at doses of 1, 2, and 3 g/kg. A validated liquid chromatography–mass spectrometry (LC‐MS) method was used for quantitative analysis and pharmacokinetic evaluation. Results The optimal preservation condition for the QDT extract and mixed standards was pH 5, 4°C, and 30 min. The analytical method showed satisfactory linearity ( r > 0.9908), precision (< 9.82%), accuracy (90.2%–109.8%), recovery (63.9%–90.8%), and matrix effects (87.64%–108.76%). Seven catechins were detected in rat plasma, whereas theaflavins were not detected under the present experimental conditions. C max and AUC generally increased with increasing dose, indicating dose‐dependent systemic exposure. Conclusion The integrated stability and pharmacokinetic evaluation establishes a link between physicochemical stability and biological disposition of QDT polyphenols, providing a scientific basis for QDT storage optimization, quality control, formulation development, and functional application.