Homogeneous Preparation Of Carboxymethyl Cellulose From Soybean Dregs And Application In Soybean Protein Isolate

Soybean dregs（SD）,as a by-product in the production of soy products,contains nutritional ingredients such as dietary fiber,which have certain utilization value.However,there are few deep processing researches of SD.In this study,synthesize sodium carboxymethyl cellulose（CMC）by one pot using soybean dregs as a raw material in the homogenous condition was developed.The structure and properties of CMC with different degrees of substitution（DS）were further studied.Based on this,the effects of CMC-3 on the properties of Ca SO₄and GDL-induced SPI gels were studied.The research results are as follows.Optimization of key parameters for the preparation of CMC from SD.Use 6%NaOH/4%urea aqueous solution to complete the purification and alkalization of cellulose,then reacting with sodium monochloroacetic acid as etherifying agent to synthesis carboxymethyl cellulose,and the degrees of substitution of CMC as research indicator.Optimized conditions for preparing CMC by single factor test and orthogonal test.The results can be summarized as follows:when the etherification time at 55℃for 3h and kept at 68℃for 1h,the soybean dregs concentration is 6.8g,the molar ratio of sodium monochloroacetic acid to cellulose is 4:1,and the concentration of NaOH is 1.5%,the pale yellow neutral product with the degree of substitution of 0.51 was obtained.The solubility of the product was 83.88%.The differences in structure and properties of CMC with different degrees of substitution prepared under three reaction conditions were discussed,the rheological properties were further studied to analyze the reaction mechanism.The FTIR spectra showed a new and strong absorption band at 1608.12cm^-1which indicated that carboxymethyl group successfully pull in.And as the degree of substitution increased,the peak area of the absorption peak increased.The changes in chemical shift in ¹H NMR indicated that hydroxy group was substituted by carboxymethyl group.In the XRD diffraction pattern,compared with the soybean dregs,the crystal form the cellulose skeleton of the prepared CMC changed from cellulose type I to cellulose type II.The diffraction peak at 2θ=22.2°shifted to the left,and the peak intensity increased.Scanning electron microscopy demonstrated that with the increase of the number of carboxymethyl substitutions,the molecular microstructure was transformed from a triangular block to a short rod,and the molecular surface gradually changed from flat and smooth to uneven honeycomb.The thermogravimetric analysis showed that as the degree of substitution of CMC increased,the high temperature resistance of the prepared CMC increased,and the thermal stability reduced.The rheological results showed that the CMC solution is a non-Newtonian fluid with shear thinning characteristics.As the concentration increased,the viscosity becomed stronger,and the viscosity increased with the degree of substitution.The effects of CMC-3 and soybean dregs on the texture and rheological of SPI gel induced by salt and acid at different concentrations were studied.The results showed that the gel strength of SPI gel prepared with Ca SO₄as coagulant and the addition of0.4g soybean dregs reached the maximum.The gradient adhesion of soybean dregs slowed down the release rate of Ca SO4,and the three-dimensional network structure was compact and water holding capacity increased.When CMC-3 was added at 0.1g,the gel strength reached the maximum,and the water holding capacity and microstructure improved.The dynamic rheological results showed that the storage modulus G’continued to increase during the cooling stage.As for the soybean protein gel induced by GDL,the strength and water retention of gel decreased after adding soybean dregs,and the network structure became loose.The microphase separation of CMC-3 and soy protein increased the concentration of gel protein,the gel strength,water holding capacity and gel microstructure were improved,and the storage modulus G’increased also.This paper is of great significance to realize the comprehensive application of soybean dregs,extend the source and application range of CMC,and improve the performance of protein gels.