Effect of Gansu starter cultures on the hypoglycemic mechanism of black bean bread

The hypoglycemic mechanism of black bean bread fermented by Gansu Jiaozi (a natural mixed starter cultures) was investigated in this study. Gansu Jiaozi was dominated by Lactobacillus plantarum, Lactobacillus brevis, and Saccharomyces cerevisiae, during the fermentation of which a significant increase in total acidity and peptide content was observed. SEM analysis revealed that black bean addition (UD groups) disrupted the gluten network of bread, while Gansu Jiaozi fermentation (SD groups) reconstructed a uniform porous structure. Notably, the formation of starch-protein/lipid complexes in black bean bread created a physical barrier that masked digestive enzyme binding sites and reduced glucose release during in vitro digestion. In diabetic zebrafish, the fermented black bean bread (SD-40 group) significantly decreased the levels of glucose (46.34%), TC (58.28%), TG (34.17%), and LDL-C (53.61%) compared with diabetic model groups (MCG), while restoring insulin and GLP-1 to normal levels. Meanwhile, fermentation-derived metabolites like organic acids and peptides might activated the AMPK and PI3K/Akt signaling pathways, significantly inhibiting the expression of phosphoenolpyruvate carboxykinase (pck-1) and pro-inflammatory factors (GLUT2 expression restored to 70.45%). These findings elucidate that fermented black bean bread exerts hypoglycemic effects through a synergistic mechanism of physical barrier and metabolism, providing novel insights and technical support for developing functional whole grain fermented foods.