Isolation and identification of an -glucosidase inhibitory peptide from extruded soybean protein and its hypoglycemic activity in T2DM mice

Although extruded soybean protein (ESPro) is currently used during the production of plant-based meats, studies involving its hypoglycemic activity in vitro and in vivo are minimal. In this study, the alpha-glucosidase inhibitory activity of ESPro with different extrusion parameters was compared and ESPro1 (160 degrees C, 30 rpm) was found to have the highest inhibitory activity. Then, simulated digestion and ultrafiltration of ESPro1 were carried out in vitro and an ESPro1 digestion product (<1 kDa) with the highest inhibitory activity was obtained. Gel filtration chromatography separation was further performed to obtain an ESPro1 F3 fraction with the highest inhibitory activity. Finally, six peptides with alpha-glucosidase inhibitory activity were screened from the ESPro1 F3 fraction and synthesized using solid-phase synthesis, among which LLRPPK showed the highest inhibitory activity (46.98 +/- 0.63%). During a four-week dietary intervention in type 2 diabetes mellitus (T2DM) mice, ESPro attenuated the trend of weight loss, reduced blood glucose, alleviated insulin resistance, and improved glucose tolerance, while ESPro1 reduced blood glucose levels by 22.33% at 28 d. Furthermore, ESPro1 significantly increased the serum high-density lipoprotein cholesterol (HDL-C) levels, decreased the low-density lipoprotein cholesterol (LDL-C) levels, up-regulated the superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activity, reduced the malondialdehyde (MDA) content, down-regulated the alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activity, and alleviated liver and pancreatic injury in T2DM mice. Overall, ESPro1 (160 degrees C, 30 rpm) displayed a superior hypoglycemic effect in vivo and in vitro and may have a beneficial impact on T2DM treatment.