Optimal synergy and pH-switch: Tea polyphenol-polysaccharide combination and modulated theabrownin activity against α-glucosidase.

This study systematically evaluated the individual and combined inhibitory effects of components (polyphenols, polysaccharides, and theabrownins) derived from the same tea cultivar on α-glucosidase. Among individual components, polyphenols from fermented tea exhibited relatively potent enzyme inhibitory activity. The inhibitory activity of theabrownins was highly pH-dependent, demonstrating significantly greater efficacy at pH 4 compared to pH 9. Structural analyses revealed that while pH alterations modified the higher-order structure and morphology of theabrownins, their core phenolic polymer composition remained unchanged. A pronounced synergistic effect was identified between tea polyphenols and polysaccharides, with optimal enzyme inhibition observed at a 5:5 ratio (interaction index γ = 0.067). Further metabolomic and quantitative analyses indicated that acidic conditions modulated the encapsulation and release of active small molecules (e.g., gallic acid, catechins, theaflavin) by regulating the material composition and molecular structure of theabrownins, thereby influencing their inhibitory activity. This study reveals an efficient synergistic combination mechanism and elucidates the pH-dependent relationship between theabrownin structure and activity, providing a foundational basis for the development of precision-engineered tea-derived functional ingredients for glycemic management.