Preparation, Characterization And Antioxidation Study Of Different Molecular Weight Of Soluble Soybean Polysaccharides

Soybean soluble polysaccharide (SSPS) extracted from soybean cotyledons has a pectin-like structure. It has been suggested that SSPS could be used in flavor emulsions because of its high water solubility, pH stability, low bulk viscosity, emulsifying properties and its ability to form strong interfacial films. Besides, SSPS has the property of being able to disperse and stabilize milk proteins under acidic conditions at a pH lower than the isoelectric point of milk proteins and has been used in acidic beverages.SSPS is an acidic polysaccharide containing galacturonic acid and its chemical structure has been characterized. SSPS is composed of a main rhamnogaturonan backbone branched by β-1,4-galactan and α-1,3-or α-1,5-arabinan chains. The molecular weight were usually between 5000-1000000 kDa. The function characteristics and application properties of SSPS were closely related to its molecular parameters such as the molecular weight. In this thesis, different molecular weight soluble soybean polysaccharides were prepared using different methods, and their characters and properties were systematically studied. The main content and conclusions were as follows:Firstly, we compared the decolorization results of the soluble soybean polysaccharides extract by the powdered activated carbon and the granular activated carbon, then the best condition for decolorization of Soybean soluble polysaccharides (SSPS) by the powdered activated carbon was studied. The amounts of Carbon, temperature, the pH and decolorization duration were evaluated by single factor experiments. Subsequently, the four factors were optimized using orthogonal array design. The optimal activated carbon amount, pH, decolorization duration, and temperature were 2%, pH3,40℃ and 40 min, respectively. The gel exclusion chromatography (GPC) result showed the average molecular weight of SSPS was 550 kDa. The polysaccharide content of SSPS was 80.96%, the protein 4.48%, the ash 8.13%, the moisture 6.07%, respectively.The process of degrading macromolecular SSPS was investigated by three methods including ultrasonic, hydrogen peroxide oxidation and hydrogen peroxide with ultrasonic treatment. It was found that hydrogen peroxide with ultrasonic treatment had the best effect for preparing low molecular SSPS. Four different molecular-weight soybean soluble polysaccharides were prepared by controlling the degration condition, they were SSPS-Y、SSPS-C、SSPS-H、SSPS-CH, with the molecular weights 550 kDa,347 kDa,285 kDa,21 kDa, respectively.Fourier transform infrared spectrometer (FTIR), X ray diffraction (XRD) and thermogravimetric analysis (TGA) were used for identification and quantification of soybean soluble polysaccharides. The FT-IR spectra obtained for soybean soluble polysaccharides with different molecular weights revealed similar significatnt peaks; different polysaccharides had the similar XRD patterns that were typical for amorphous structure with a major crystalline reflection at 21°; the thermal stability and degradation behavior of SSPS-Y was evaluated by TGA under nitrogen atmosphere. The first mass loss was attributed to the loss of structural water and the second weight loss event with an onset of over 270℃ resulted from thermal decomposition. Different polysaccharides after degradation were similar to SSPS-Y besides the lower decomposition temperatures and weight losses.Several in vitro assays were applied to evaluate the antioxidant potential of SSPS, such as the scavenging ability on DPPH radical and hydroxyl radical, also we studied the reducing power of different polysaccharides determined at 700 nm. Results indicated that the four polysaccharides with different molecular weights showed different antioxidant activities with different evaluation system. The SSPS-H with molecular weight of 285 kDa had the strongest antioxidant activities in all antioxidant systems, while the SSPS-CH with molecular weight of 21 kDa performed the worst.