Study on the Enhancement of Hypoglycemic and Antioxidant Activities of Compound Herbal Tea through Solid-State Fermentation

This study utilized Aspergillus niger KY2295 for the Solid-State Fermentation (SSF) of a compound tea made from Cinnamomum cassia bark, Glycyrrhiza glabra, Morus abla L. leaf, and Crataegus oxyacantha L. to enhance its hypoglycemic effects. The fermentation process was optimized using single-factor experiments and a Central Composite Design (CCD), with α-amylase and α-glucosidase inhibitory activities as evaluation indices. Following fermentation, increases were observed in active compounds, including total phenolics, flavonoids, polysaccharides, proteins, and free amino acids. In vitro antioxidant activities—2,2-Diphenyl-1-Picrylhydrazyl (DPPH), 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and hydroxyl radical scavenging—were enhanced, contributing to increased enzyme inhibition. The optimal conditions (3.88% inoculum, 30.01℃, 73.50 h) yielded these two enzymes inhibition rates of 62.21±1.94 and 72.39±1.18%, respectively. DPPH, ABTS, and hydroxyl radical scavenging increased by 18.47, 47.55, and 20.22%, respectively.  Furthermore, the inhibition rates of α-amylase and α-glucosidase rose by 43.37 and 54.84%. These results demonstrate that SSF significantly enhances the bioactive content, hypoglycemic and antioxidant activities of the herbal tea, suggesting potential for its development as a functional food.