Inhibitory Mechanism of Characteristic Polyphenols in Hainan Large-Leaf Tea against Carbohydrate Hydrolases

This study explored the inhibitory potential and mechanism of water extracts and characteristic polyphenols from green and black tea made from the Hainan large-leaf variety against carbohydrate-hydrolyzing enzymes (α-amylase and α-glucosidase). The results showed that green tea had significantly higher total phenolic (61.9 mg/g) and flavonoid (28.79 mg/g) contents and consequently exhibited stronger inhibition against α-glucosidase and α-amylase with half maximal inhibitory concentration (IC₅₀) of 59.10 μg/mL and 14.21 mg/mL than black tea, respectively. Nine characteristic polyphenols were identified, and five core active monomers including epigallocatechin (EGC), epigallocatechin gallate (EGCG), procyanidin B₂ (PB₂), kaempferol-3-O-rutinoside, and ellagic acid were screened out by molecular docking. These compounds demonstrated significant enzyme inhibitory effects and enhanced glucose consumption in 3T3-L1 cells. Mechanistic analysis revealed that the polyphenols inhibited the enzymes in competitive, non-competitive, and mixed-type manners. Fluorescence quenching and molecular simulations confirmed that the polyphenols could interact with the enzymes’ active sites (ASP-300/GLU-233 in α-amylase; GLU-296/ASP-269 in α-glucosidase) via a static quenching process, and stable complexes were formed through hydrogen bonding and van der Waals forces, with EGCG-α-amylase and PB₂-α-glucosidase complexes showing optimal stability. This study demonstrates that the characteristic polyphenols in Hainan large-leaf tea, particularly in green tea, regulate postprandial glucose through the dual pathways of enzyme inhibition and glucose consumption promotion. At their core, these polyphenols stably bind to the active sites of carbohydrate-hydrolyzing enzymes through multiple mechanisms.