Comparative study on physicochemical properties and hypoglycemic activities of intracellular and extracellular polysaccharides from submerged fermentation of Morchella esculenta

The structural characteristic, physicochemical properties and structure-hypoglycemic activity relationship of intracellular (IPS) and extracellular (EPS) from submerged fermentation of Morchella esculenta were systematically compared and assessed. Both IPS and EPS were neutral, with a triple-helical conformation, and composed of galactose, glucose and mannose monosaccharides in different molar ratios. The molecular weight and particle size of IPS were higher than those of EPS. FTIR and SEM showed that the main functional group absorption peak intensity, glycosidic bond type and surface morphology of the two polysaccharides differed. Analysis of rheological and thermal properties revealed that the viscosity of IPS was higher than that of EPS, while thermal stability of EPS was greater than that of IPS. Hypoglycemic activity analysis in vitro showed that both IPS and EPS were non-competitive inhibitors of alpha-amylase and alpha-glucosidase. EPS showed strong digestive enzyme inhibitory activity due to its higher sulphate content and molar ratio of galactose, lower Mw and particle size. Meanwhile, with its higher Mw and apparent viscosity, IPS showed stronger glucose adsorption capacity and glucose diffusion retardation. These results indicate that IPS and EPS differed considerably in structure and physicochemical properties, which ultimately led to differences in hypoglycemic activity. These results not only suggested that IPS and EPS has the potential to be functional foods or hypoglycemic drugs, but also provided a new target for the prevention and treatment of diabetes with natural polysaccharides.