Physicochemical characterizations, α-amylase inhibitory activities and inhibitory mechanisms of five bacterial exopolysaccharides.

Inhibiting pancreatic α-amylase activity can decrease the release rate of glucose, thereby delaying postprandial blood glucose. This study aimed to investigate the physicochemical properties and porcine pancreatic α-amylase (PPA) inhibitory activities of five bacterial exopolysaccharides (EPSs). We also aimed to analyze the differences of their inhibitory activities, exploring the inhibition mechanism between EPSs and PPA. Five EPSs had a low molecular weight (55-66 kDa), which were mainly composed of mannose and glucose with total content exceeding 86 %. The IC50 values of five EPSs (0.162-0.431 mg/mL) were significantly lower than that of acarbose (0.763 mg/mL), indicating that the inhibitory effects of five EPSs on PPA were stronger than acarbose, especially the EPS from Bacillus subtilis STB22 (BS-EPS). Moreover, BS-EPS was a mixed-type inhibitor, whereas other EPSs were noncompetitive inhibitors of PPA. Five EPSs quenched the fluorophore of PPA by the mixed quenching or apparent static quenching. Interestingly, BS-EPS showed stronger binding affinity to PPA than other EPSs. It can be speculated that EPSs with low molecular weight, high carboxylic acid content, and α-glycosidic bond exhibited high PPA inhibitory activity. These results suggest that BS-EPS can effectively inhibit PPA activity and has potential applications in reducing postprandial hyperglycemia.