A popular non-alcoholic beverage worldwide, tea can regulate blood glucose levels, lipid levels, and blood pressure, and may even prevent type 2 diabetes mellitus (T2DM). Different tea fermentation levels impact these effects. Tea products with different fermentation degrees containing different functional ingredients can lower post-meal blood glucose levels and may prevent T2DM. There are seven critical factors that shed light on how teas with different fermentation levels affect blood glucose regulation in humans. These factors include the inhibition of digestive enzymes, enhancement of cellular glucose uptake, suppression of gluconeogenesis-related enzymes, reduction in the formation of advanced glycation end products (AGEs), inhibition of dipeptidyl peptidase-4 (DPP-4) activity, modulation of gut flora, and the alleviation of inflammation associated with oxidative stress. Fermented teas can be used to lower post-meal blood glucose levels and can help consumers make more informed tea selections.

Fermentation significantly influences the chemical composition of black tea, yet the effects of different fermentation temperatures on non-volatile components and their in vitro hypoglycemic activity are insufficiently studied. This research investigates how varying temperatures (20, 25, and 30°C) affect the bioactive profile and the inhibitory activity of Jinxuan black tea against α-glucosidase and α-amylase. Our results show that lower fermentation temperatures (20°C) lead to elevated levels of key bioactive compounds, including tea polyphenols (9.24%), soluble sugars (8.24%), thearubigins (7.17%), and theasinesin A (0.15%). These compounds correlate strongly with enhanced α-glucosidase inhibition (R = 0.76–0.97). Non-targeted metabolomic analysis revealed that 36 differential metabolites, including catechins, exhibited altered levels with increasing fermentation temperature. Notably, tea fermented at 20°C exhibited superior hypoglycemic activity, with α-glucosidase inhibition (IC₅₀ = 14.00 ± 1.00 μg/ml) significantly outperforming α-amylase inhibition (IC₅₀ = 2.48 ± 0.28 mg/ml). The findings of this research underscore the importance of fermentation temperature in optimizing the bioactive profile of black tea. It is proposed that recommendations for future processing or formulation should emphasize the use of lower fermentation temperatures, aimed at augmenting the health benefits linked to higher polyphenol content and stronger hypoglycemic activity.

Single-source Jinxuan (Camellia sinensis) tea leaves were processed into teas with varying fermentation degrees to minimize genetic and environmental interference. Non-volatile component differences between fermented and non-fermented teas were identified, with fermented teas showing reduced tea polyphenols and soluble sugars but elevated theaflavins and theasinensin A(TSA). Fermented teas exhibited stronger in vitro digestive enzyme inhibition, particularly α-glucosidase (α-Glu), with TSA (R = 0.97) and theaflavin-3-gallate (R = 0.93) showing the strongest correlations (p < 0.001). In vivo, TSA's hypoglycemic effect in diabetic mice was mediated by enhanced insulin secretion, linked to lipid, amino acid, and fatty acid metabolism. These findings elucidate fermented tea's superior digestive enzyme inhibition and provide a foundation for optimizing hypoglycemic effects through processing.