Structural And Functional Properties Of Water-soluble Polysaccharide From Soybean (glycine Max) And Mung Bean (vigna Radiata L.) Hull

The extraction, purification, physicochemical properties, structural analysis, in vitro antioxidant activity, of polysaccharide from soybean and mung bean hull, as well as in vitro bile acid binding capacity and hypolipemic effects were investigated in this study. The main contents and results are as follows:The main compounds in soybean hull are insoluble fiber, soluble fiber and protein. On the basis of single-factor experiments, the extraction technique of soybean hull polysaccharide was optimized by quadratic general rotary unitized design. The results showed that the optimum extraction conditions of soybean hull polysaccharide were pH of 5.5, ratio of water to solid of 25:1 (mL:g), extraction temperature of 90℃, extraction time of 68 min. Under these conditions, the yield of soybean hull crude polysaccharide (SCP) was 10.17% by two-time extraction. Similarly, the response surface analysis (RSA) was used to optimize the extraction conditions of mung bean hull crude polysaccharide (MCP). The best extraction conditions were pH value of 4.6, ultrasonic power of 155 W, extraction time of 40 min, and repeated 3 times. In this case, the yield of MCP was up to 8.54 %.After deproteinization by Sevag reagent and decoloration by macroporous absorbent resin, the pre-purified polysaccharide SHP and MHP were obtained. Subsequently, SHP and MHP were fractioned by DEAE-cellulose anion exchange column and purified by Sephadex G-100 gel permeation column. There were three fractions obtained from SHP marked SHP1, SHP2 and SHP3, and two from MHP marked MHP1 and MHP2. The yields of five fractions were 24.31%, 49.70%, 11.52%, 27.63%, and 59.21%, with molecule weights of 149342 Da, 72799 Da, 45554 Da, 83236 Da, 45012 Da, respectively.The evaluation of antioxidant activity of polysaccharide fractions was carried out. The results indicated that the antioxidant capacities of MHP, MHP1 and MHP2 increased with the concentration. Furthermore, The reducing power, antioxidant activity, scavenging activity of O ?2?, ? OH and DPPH free radical, as well as inhibition effects of self-oxidation of 1,2,3-phentriol of MHP, MHP1 and MHP2 were stronger than those of SHP, SHP1, SHP2 and SHP3. Besides, MHP1 exhibited the best antioxidant activity among these three substances. The comparison of the ability to bind bile acid in vitro of seven substances demonstrated that SCP and MCP could bind more bile acid than purified fractions. These results indicated that the ability to bind bile acid of polysaccharide was affected by the purification process, physical and chemical structures of purified fractions or active binding sites.The Fourier transformation infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR) analysis, gas chromatography (GC), partial acid hydrolysis, periodate oxidation– Smith degradation and methylation analysis were adopted to characterize the structures of SHP1, SHP2 and SHP3. The purified fractions were acid heteropolysaccharide without protein or nucleic acid. The content of uronic acid was 17.31%, 57.36%, 26.71%, respectively. Moreover, the neutral sugar of SHP1 mainly was mannose and galactose, while SHP2 consists of rhamnose, galactose and arabinose, SHP3 contains arabinose, mannose and rhamnose.Methylation analysis indicated that the main chain of SHP2 was the repeated units of→2)Rhap(1→4)GalA(1→2Rhap(1,4→, and the main branched chain of SHP2 was glycan composed by→1)Araf(3,5→)Araf(3→and→1)Galp(6→3)Araf(1→)Galp(6→.The polysaccharides from soybean and mung bean hull could adjust the blood lipid level of mice with high fat diet significantly. After lavage of fraction SHPb and fraction MHPa at the dose of 50 mg/kg·bw and 180 mg/kg·bw for 4 weeks, respectively, the excessive increase of body weight was inhibited. The levels of serum TC, TG, LDL-C and atherosclerotic index (AI) reduced while HDL-C increased significantly. And, the levels of hepatic TC, TG were effectively maintained in a healthy status. Additionally, MHPa could lower the serum and liver malondialdehyde (MDA) concentration of mice with high fat diet and increase activity of SOD and GSH-Px. Obviously, the polysaccharides from soybean and mung bean hull could promote the excretion of TC and bile acid, and lessen the risk of hyperlipoidemia.