Determination of potential α-glucosidase inhibitors in Jinxuan black tea based on bioaffinity ultrafiltration...

The search for natural α-glucosidase (α-Glu) inhibitors has gained significant attention in developing novel antidiabetic agents or functional foods. Low-temperature fermented Jinxuan black tea represents a promising source of such bioactive compounds. Sixteen potential α-Glu inhibitors were identified from the tea using 10 kDa affinity ultrafiltration. Key compounds, including theaflavin (TF), theasinensin A (TSA), epicatechin gallate (ECG), epigallocatechin gallate (EGCG), and gallocatechin gallate (GCG), were identified. The inhibitory activity was assessed via IC₅₀ determination, with TSA showing the highest potency. Structural mechanisms were investigated through fluorescence spectroscopy, circular dichroism, and molecular docking. TSA exhibited remarkable α-Glu inhibition (IC₅₀ = 5.53 ± 0.10 μM) and was the abundant active constituent (3.03 ± 0.17 mg/g). Oxidative dimerization of EGCG to form TSA enhanced inhibitory effects, primarily mediated by hydrophobic interactions and hydrogen bonding, with the 7-OH group on the A ring playing a critical role. The hypoglycemic effect of low-temperature fermented Jinxuan black tea is largely attributed to TSA's potent α-Glu inhibition. These findings provide mechanistic insights into black tea's antidiabetic properties and support its potential application in functional food development.