The Enzymatic Preparation, Properties And Application Of Water-soluble Dietary Fiber From Corn Bran

This study uses a two-step enzymatic method to prepare water-soluble dietary fiber(SDF)from corn bran. Optimization experiments were adopted to explore the best technologicalconditions of enzymolysis process. At the same time, take research of the SDF properties,structure and applications in beverages. This study provide a theoretical basis and technicalsupport for deep processing of corn resources, have a good application prospect.Firstly, enzymatic process to prepare corn bran SDF was simplified. The method wasdifferent with the existing enzymolysis technology, which had three enzymolysis steps.Thestudy prepared SDF by a two-step enzymatic method, the first step was using fractionatedadding enzyme, segmented control, a one-time separation method to remove protein andstarch on the surface of corn bran, the second step was using enzyme to restrictive modifiedinsoluble dietary. The results of first step indicated that the optimal enzymolysis conditions ofneutral protease were as follows: addition amount0.6%, temperature42°C, pH7.5,enzymolysis time3.5h. Then the temperatured was adjusted to65°C and complex enzymeswere added. Enzymolysis conditions were as follows: addition amount0.3%, pH5.5,enzymolysis time1h. After separation, the surface protein and starch of corn bran wereremoved almost completely，post-processing raw protein content decreased from9.21%to0.76%, starch content decreased from12.34%to0.58%. The second enzymolysis conditionswere as follows: addition amount0.8%, temperature58°C, pH5.5，enzymolysis time8h.Under this condition, SDF yield was13.82%, the purity was95%or more. Color, state andsolubility of spray drying product and freeze drying product are very good, is a yellow-whitepowder with a faint scent. Compared to previous studies, this process obtained the targetproduct by only two steps. The technology had short production cycle and low energyconsumption, advoided waste of resources and energy caused by adding water and risingtemperature in the original process, which was suitable for industrial production.Secondly, the properties and structure of corn bran SDF were studied. Solubility study ofSDF showed that the solubility increases with the increasing temperature, at80°C, thesolubility reached55.20%; solubility under neutral condition is greater than the solubilityunder acidic and alkaline conditions. The rheological properties study of SDF showed that,the solution viscosity increased significantly with the increasing concentration, decreasedwith the increasing temperature,less affected with pH, and viscosity is minimum in weaklyacidic or neutral conditions, less changed in the high-salt and high-sugar solution. In certainconcentration range, viscosity of corn bran SDF solution decreased with shear rate increased,showing shear-thinning properties, and as the concentration increases, the shear-thinningproperties were more obvious. Compare with soybean polysaccharides, study found corn bran SDF had the higher solubility and the lower viscosity. The color stability study of SDFshowed it had good color stability and its transmittance impacted less by heat treatment,different pH and light. Therefore, corn bran SDF has a relatively wide range of applications.In vitro assay showed that the abilities of absorbing saturated fat of the dietary fiber isbetter than the abilities of absorbing unsaturated fat, abilities of absorbing bile sodium andcholesterol of the dietary fiber were affected by the reaction system pH, and the adsorptioncapacity under neutral conditions was higher than acidic conditions. Meanwhile, the abilitiesof absorbing fat, bile sodium and cholesterol of corn bran SDF were stronger than the IDF.Molecular weight analysis showed, SDF molecular weight is relatively small, molecularpolymerization degree is low, and the molecular weight of the main component is30611,content of54.85%. IR spectra analysis shows samples have the typical features ofpolysaccharides.Finally, the corn bran SDF was applied in different beverages. In the formulated milkbeverage, when the adding amount of SDF was1%-7%, the system was stable, uniform state,had no layering or no precipitation phenomenon, and SDF would not bring it thick taste, haveno bad effect on appearance and flavor of product. In the fermented milk drink, when theadding amount of SDF was1%-5%, precipitation rate was low, and had a uniform distributionsystem and no whey separation. SDF could slow the viscosity decrease in fermented milkbeverage during storage, and improve its taste, but promote the post-fermentation and resultedin rapid decline of pH, so the adding amount should be controlled in a certain range. In thejuice, when the adding amount of SDF was1%-8%, it had good stability and low viscosity.SDF could be added to improve the stability of juice during the later stage of storage,furthermore juice could maintain a fresh taste and transmittance.