Research On The Gel Properties And Microstructure Of Soybean Protein-polysaccharide Composite System

Polysaccharide and protein are the main functional food ingredients, they have crucial effect on texture and taste of food. When protein and polysaccharides in the same system, phase separation occurred because of the thermodynamics incompatible between two kinds of biological macromolecules. In this paper, the phase behavior, rheological properties, texture, microstructure, the gelation kinetics and mechanism of soybean protein/polysaccharides were studied systemically by combination use with phase diagram analysis, dynamic rheolog, texture analysis, scanning electron microscope and confocal laser scanning image analysis methods. The main results are as follows:1. The rheological and thermal properties ofβ-conglycinin/dextran mixed gels were investigated. As results showed,the increase in molecular weight and concentration of dextran can improve the gel strength greatly. High molecular weight and high concentrations of dextran significantly increased occupy effect so as to promote the phase separation.With the concentraion of NaCl increased,the gel strength ofβ-conglycinin/dextran mixed gels were improved.2. The gel properties and microstructure of GDL-induced soy protein gel were studied.The results showed the pH and gel strength of glycinin are depend on the total acidification rate.With the increasing acidification rate, the gel strength increased and then decreased.In the condition of low acidification rate,the microstructure is homogeneous.In the condition of high acidification rate,the microstructure is rough and large porosity.3. The reology and texture properties of cold-set soybean SPI/dextran mixed gel were investigated.The results showed the gel point showed later and the final gel strength depend on the total acidification rate. The elastic moduli of gel increased and then decreased with the increase of the dextran concentration. Increasing the molecular weight of dextran results in the elastic moduli of gels changed dramatically.4. The phase behaviour,reology properties and microstructure of GDL-induced 11S/LBG mixed gel were investigated systematically. The results showed the reology properties,texture properties and microstructure of mixed gels depend on the competition between the phase separation and gelation. Phase separation occurred at the gel point and become more obviously in the process of gelation. The presence of a lower LBG led to a large enhancement of viscoelastic moduli of mixed gels. But higher polysaccharide concentrations could lead to phase separation in the mixed systems due to their thermodynamic incompatibility. Gels microstructure with low polysaccharide concentration showed morphologies with LBG microphase separated into a protein continuous network and discontinuous serum phase with sharp phase boundaries.With appropriate protein concentration increase, ratio for GDL / protein becomes smaller, result elasticity increased.Further increasing the protein concentration gel structure gets weaker. Phase separation of high protein concentration is significant. With appropriate acidification rate during mixed gels gelation process causes a dramatic increase in storage modulus and gel strength. However, with increasing acidification rate by excessive GDL addition would weaken gel network structure. In addition ionic strength enhancement accelerates phase separation occurred in glycinin/LBG system due to addition of NaCl reduces the electrostatic repulsion between charged protein molecules.However, it also can be found that continuing adding sodium ions would weakening of glycinin/LBG gel strength and cause gel structure collapse.5. The transparent cold 11S gels were formed by the addition of Dextran sulfate.The research results showed gels become weaker but transparency with DS concentration increases.Dextran sulfate has inhibitory effect of the 11S aggregate.With the increase of the DS concentration,the inhibition effect is remarkable.The effect of DS on inhibition aggregate is decreased attribute to the electrostatic shielding effect of salt ions.The effects of DS in inhibiting are primarily by the changes in charge, that is mainly rely on the electrostatic interactions between 11S and DS. DS gathered and formed 11S crosslinking soluble aggregates. But the salt ions reduced the formation of soluble aggregates and created more non-soluble aggregates.