Development And Research On High Oligosaccharides-Containing Okara Dietary Fiber

In this paper, okara was used as materials to determine the optimum parameters to improve the soluble dietary fiber (SDF) content in okara of the blasting extrusion technology and cellulase hydrolysis method. The physicochemical properties, monosaccharide composition and structure of the extracted okara SDF were determined. The optimum parameters of β-mannanase hydrolysis in improved the oligosaccharides content of okara SDF were also studied and main component of the oligosaccharides were separated.The optimum parameters of blasting extrusion were:diameter of mold hole4mm, temperature171℃, screw speed155r/min. In this condition, the okara SDF content was24.13±0.13%.This method improved the SDF content in okara while had no adverse effect on other components. In addition, the extruded okara had higher water retention capacity, water solubility, and swelling capacity than that of dietary fiber in raw okara. The extruded okara had a good thermal stability below200℃based on the analysis of a differential scanning calorimeter (DSC). The structure of extruded okara appeared degradation observed using the scanning electron microscopy (SEM) compared with raw okara.The optimum parameters of further improved the SDF content of extruded okara with cellulase enzymatic method were:enzymatic temperature50℃, enzymatic time3h, enzyme amount (the mass ratio of enzyme and the substrates)1:500. In this condition, the SDF content of enzymolysis okara was30.10±0.17%.The extracted okara SDF was pale yellow solid, soluble in water, insoluble in ethanol or other organic solvents. Water solubility was19.2g/100g, total sugar content65%, protein content1.9%, uronic acid content of24.2%, no starch or reducing sugar. HPLC results showed that the molecular weight of the main polysaccharide in okara SDF was117,096Da, the content was91.87%. Eight types of monosaccharides were identified by GC in the SDF, the concentrations of galactose and mannose (39.81%and31.78%, respectively) were at higher level. Macroporous resin AB-8can effectively bleached the SDF, after bleaching the SDF were white solid. IR result showed the SDF had a typical polysaccharide structure.The optimum parameters of preparation of high oligosaccharides content SDF according to β-mannanase enzymatic method were:enzymatic temperature60℃, enzymatic time4h, enzyme amount (the mass ratio of enzyme and the substrates)1:50. After enzymatic hydrolysis, the mixture was subjected to ultrafiltration by Hollow fiber ultrafiltration membrane. The filtrate was concentrated and lyophilized, the yield of crude oligosaccharide was37.67%. High performance liquid chromatography (HPLC) analyze showed that the crude oligosaccharide had four kinds of oligosaccharide with different degree of polymerization, total amount was27.65%. The degree of the oligosaccharide may be eight when speculated based on the molecular weight. A major oligosaccharide component was obtained when separated the oligosaccharide fractions with dextran gel Sephadex G25. The purity of the main component was verified by Sephadex G15, the results showed that the separated component was a single component oligosaccharide. After calculation, the okara oligosaccharides content obtained through this research was3.7g/100g dry okara.