Comparison of Structural Characteristics and Major Biological Activities of Polysaccharides from Soybean and Natto

In this study, crude polysaccharides from soybean and natto were prepared by water extraction followed by ethanol precipitation. The chemical compositions, structural characteristics, water solubility, water-holding capacity (WHC) and fat-binding capacity (FBC) of soybean and natto polysaccharides were analyzed. Their in vitro antioxidant, hypoglycemic, and lipid-lowering activities were compared and analyzed. The results showed that the content of uronic acid was significantly higher in natto polysaccharide than in soybean polysaccharide (P < 0.05). The molecular masses of soybean and natto polysaccharides were 5.256 and 33.532 ku, respectively, and the monosaccharide compositions of soybean and natto polysaccharides were similar in the types but different in the proportions of monosaccharide. The surface of soybean polysaccharide was rough, whereas the surface of natto polysaccharide was smooth and dense. The water solubility of natto polysaccharide was 2.04 times as high as that of soybean polysaccharide, and the FBC was 2.99 times as high as that of natto polysaccharide. Natto polysaccharide exhibited better antioxidant activity, with half maximal inhibitory concentration (IC₅₀) of (0.049 ± 0.015) and (2.640 ± 0.072) mg/mL for scavenging of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical, respectively. The IC₅₀ for the inhibition of α-amylase activity by natto polysaccharide was (3.297 ± 0.395) mg/mL. Natto polysaccharide had significantly higher in vitro hypoglycemic activity (P < 0.05), stronger cholate binding capacity and in vitro hypolipidemic activity than soybean polysaccharide. This study has provided an important theoretical basis for the structural analysis and biological activity evaluation of natto polysaccharide.