Study On Gelation Of Soy Protein And Preparation And Properties Of EDTAD Modified Soy Protein Gels

Gelation is one of the most important functionality of soy protein. Gelation and hydration of soy protein are improved by chemical modification. In the thesis, a soy protein gel is prepared and and a modified soy protein gel is synthesized by first acylating the soy protein isolate with ethylenediaminetetraacetic dianhydride(EDTAD), followed by crosslinking with glutaraldehyde. The swelling ratio, texture, structure of soy protein-based gels and main affecting factors of which are researched;the swelling behavior, biodegradability and rheology properties at crosslinking process of modified soy protein gels are discussed. The main contents and related original achievements are as follows:1. A soy protein gel is prepared and the main factors which affecting the swelling ratio of soy protein gels are researched. The experimental results have shown that the swelling ratio change with the increasing of concentration of protein, the optimal concentration of protein is 13% at which the largest swelling ratio is got;the swelling ratio increases by adding appropriate K⁺ or Ca²⁺, but further increase of content of ions causes decrease of the swelling ratio because of decrease of the osmotic pressure of gels network;the effect of solvent ethanol on the swelling ratio is not obvious, but which of crossling agent glutaraldehyde is obvious;the texture analysis results show that addiotion of appropriate amount of K⁺ or Ca²⁺ causes increase of the hardness and cohesiveness of gels, crosslinking of glutaraldehyde causes increase of the hardness, cohesiveness and springiness of gels obviously. The scanning electron microscope(SEM) pictures show that the microstructure of soy protein gelcrosslinked by glutaraldehyde is clearer than that without glutaraldehyde.2. The modified soy protein gel is synthesized by heating soy protein at 65°C/pH12 for 30 min, then acylating wih EDTAD at 25°C/pH12 , followed by crosslinking with glutaraldehyde. Through determining content of lysyl residue and carboxyl moities of modified soy protein , acylation reaction mode is analyzed. The experiment data have shown that acylation reaction is carried out according to such a ratio: about 3 carboxyl moieties per lysyl residue are incorporated into soy protein when mEDTAD:nispi is 0.1 or 0.3;partial crosslinking may occur when niEDTAi>nispi is UP t0 0-5- The swelling properties and effect of mass ratio of reagents are investigated, the results show that the optimal swelling ratio is 95.87 at mEDTAr>nispi = 0.2 and mSpi:mGiu = 90:2. The microstructure of gels is scanned by scanning electron microscope(SEM), it appears that modified soy protein gels have highly ordered microstructure.3. Through differential scanning calorimetry(DSC) and thermogravimetry(TG), the state and content of water in soy protein gels are analyzed, the results are as follows: the water in soy protein gels includes non-freezing water and freezing water;the content of nonfreezing water in soy protein gels decreases with growth of K+ percentage, and increases with growth of Ca2+ percentage;the content of non-freezing water in modified soy protein gels increases with iriEDTAi>nispi. The content of different states of water in soy protein gels is affected by additive ion or incorporated functional group.4. The equilibrium swelling ratio and swelling behavior of soy protein gels are studied. The resuts show that the swelling ratio of modified soy protein gels decreases with growth of protein concentration during crosslinking step, but lower protein concentration makes softer gels, which means that gels are prepared at a proper protein concentration;theeffect of pH on the swelling ratio of modified soy protein gels is obvious, gels have appeared pH-sensitivity;ionic strength and gel particle size have a little effect on swelling ratio of gels. The swelling data are analyzed by mathematical method, the results are as follows: modified soy protein gels with mEDTAD:mSpi as 0, 0.05, 0.1 or 0.2 appear Fickian's diffusion behavior in water;at alkaline pH, gels have appeared the same behavior , but appeared non-Fickian's diffusion behavior at acid pH because of shrinking of gel network.5. The biodegradability of modified soy protein gels is demonstrated by enzyme hydrolysis and a fungal overgrowth test. After 60 hr proteolysis, modified soy protein gels are completely hydrolyzed by trypsin. SDS-PAGE picture shows that 7S and US subunit of enzymatic hydrolyzed products disappeared;GPC diagrams show the molecular weight range of enzymatic hydrolyzed products are from 100 to 9000. After a 28 days incubation with fungal spores the gel particles are dissolved completely and covered by growing fungal. The results have proved fully biodegradability of modified soy protein gels.6. The change of reological parameters in crosslinking process of modified soy protein with glutaraldehyde are investigated. The storage modulus(G') of modified soy protein system increases pronouncedly and the loss modulus(G") of it increased to a lesser extent, so tangent of phase angle(tan 8 ) decreased. This indicates that increasing of elasticity in the system has become a main trend , and increasing extent of adhesion in system is not enough to counteract that of elasticity. A more elastic gel matrix with three-dimensional network is formed at the process. A larger niEDTAi>nispi value causes a larger G' in gels, and a larger amount of glutaraldehyde causes a larger G' and initial crosslinking velocity which result from different effect of EDTAD and glutaraldehyde.