| Okara is the main by-product from soymilk and tofu preparation, contains more than 60% of dietary fiber. Although the resource of the okara is rich all over our country, most of them is used as feed, or even discarded as waste, which dietary fiber is not fully utilization. Therefore, a comprehensive development and utilization of okara, not only can reduce this resource waste, but also can create more values and bring new growth point in agriculture and economic development. In this study, we use the okara as raw material, okara dietary fiber was obtained from a reaction by protease alkaline hydrolysis process of okara and optimize the alkaline hydrolysis conditions, then studied on protein removal methods and particle sizes effects on chemical composition and functional properties of dietary fiber from okara, and studied chemical composition and in vitro antioxidant properties of three groups of soluble dietary fiber we obtained through different ethanol fractional precipitation.The protein removal as index, alkaline protease was chosen as the best enzyme in preparing okara dietary fiber from the tested six proteases. The optimal process parameters were obtainded through the typical analysis and ridge analysis as follows:pH 9.0, extraction temperature 55.47 ℃, extraction time 2.5 h, enzyme substrate ratio 4262.63U/g, the ratio of water 1:10. Okara protein removal was up to 78.56% under the condition.The combined effect of four protein removal methods(alkaline protease, neutral protease, flavor protease, alkaline extraction) and ultrafine grinding on the characteristics and physicochemical properties of dietary fiber(DF) from okara were investigated. The results showed that protein removal could effectively increase dietary fiber contents and functional properties(water holding capacity, water retention capacity, swelling capacity and oil holding capacity). As particle size decreased, the content of soluble dietary fiber was increased. However, the functional properties(WHC, SC, WRC) were significantly decreased, the OHC was decreasing firstly and then increasing with the particle size decreasing. The functional properties of okara DF prepared by alkaline enzyme treatment combined with ultrafine grinding were better.By cellulose and a-amylase enzyme extraction of okara soluble dietary fiber, and then we obtained three groups of soluble dietary fiber named SDF-1, SDF-3, SDF-5 through ethanol fractional precipitation(1, 3 and 5 volume ratios to the liquid medium), enzymatic combined with TCA removing protein and dialysis. Research on the composition and in vitro antioxidant capacity of three groups soluble dietary fiber. It turned out that SDF-1, SDF-3 were all white, SDF-5 was brown, the component content of was SDF-1, SDF-3, SDF-5 was significant differences. The ability of DPPH radical, capacity of ABTS radical and reducing power of SDF-5 is much higher than SDF-1, SDF-3, IC50 of free radicals is 0.4 mg/m L, 160 ug/m L, IC0.3 of reducing capacity was 150 ug/m L. Fourier infrared spectrum showed that three kinds of SDF extract had the typical characteristic absorption peaks(3400 cm-1, 2930 cm-1, 1662 cm-1, 1070 cm-1, 893 cm-1). Analysis of monosaccharide composition in the SDF by gas chromatography revealed that SDF-1 was composed of L-arabinose, D-mannose, D-Glucoseand D-galactose with mass mass ratio of 1.21: 1.60: 4.90: 1.33, but SDF-3 and SDF-5 were composed of L-rhamnose, D-arabinose, D-xylose, D-mannose, D-glucose and D-galactosewithmassratio of 2.00: 4.05: 0.98: 0.84: 0.96: 13.64 and 1.46: 4.75: 1.04: 2.10: 1.64: 23.92. By comparing the components and in vitro antioxidant capacity, infrared spectrum and ultraviolet spectrum, monosaccharide composition of three groups SDF, gets activity SDF in okara, this will provide theoretical and technical guidance to get highly active okara SDF. It is also of a great significance to deeply development of okara and highly value of utilization. |
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