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.

Partridge tea (Mallotus oblongifolius Muell-Arg), an important and widely consumed substitute tea in Hainan, China, possessed multi-biological activities. This study investigated the composition and content of phenolics-rich extracts purified from partridge tea, and then explored the effect of partridge tea polyphenol extract (PTE) on glucose and lipid metabolism disorders in type 2 diabetes mellitus (T2DM) mice. The results showed that the dominant components in PTE included rutin ((63.78 ± 1.86) mg/g), 3-chlorogenic acid ((85.81 ± 3.48) mg/g), caffeic acid ((152.78 ± 2.93) mg/g), catechin ((12.10 ± 1.41) mg/g), gallic acid ((5.24 ± 0.12) mg/g), kaempferitrin, ellagic acid, ferulic acid, caffeic acid methylester, and geraniin. After 6 weeks of PTE intervention, glucose tolerance, insulin resistance, and pancreatic β-cell function in T2DM mice had significantly improved. This improvement was corroborated by an increase in glucagon-like peptide-1 (GLP-1) to homeostasis model assessment of β-cell function (HOMA-β), glycogen, insulin protein expression, and reduction in insulin levels, glycosylated serum protein (GSP), homeostasis model assessment-insulin resistance index (HOMA-IR), glucagon protein expression. The supplementation of PTE also seems to alleviate the inflammatory response, as evidenced by a decrease in endotoxin and inflammatory cytokine levels. Hyperglycemia-induced mitochondrial damage is alleviated by PTE intervention. Hematoxylin-eosin staining (H&E staining) and lipid profile analysis indicate that PTE intervention can help regulate lipid metabolism disorders. In addition, the integration of metabolomics and transcriptomic analysis indicates that PTE intervention could regulate glycolipid metabolism pathways related to T2DM, including insulin, AMPK, bile acid metabolism and glutathione metabolism signaling pathways. More importantly, the validation results from reverse transcription-polymerase chain reaction (RT-PCR) confirmed that the expressions of Scd1, Fasn, Hmgcr, and Slc2a4 (related to glycolipid metabolism) were consistent with the transcriptomics data. In conclusion, these results suggested that PTE may exhibit significant health promoting effects for T2DM mice.