Studies On Mechanism Of Soy Protein Isolate-Chitosan Interaction And Complex Formation

The formation mechanism and application of protein-polysaccharide complexes has received considerable attention in food research field.Soy protein isolate is one kind of high quality vegetable protein with rich nutrition which can be used as substitute for animal proteins.As the second most abundant natural polysaccharide which is inferior to cellulose,chitosan(CS)has been widely applied in food,medicine,chemical industry and so on.In this study,soy protein isolate(SPI)-chitosan(CS)mixture was extensively investigated to study the influence of different pH value and the ratio of protein/polysaccharides on the properties of composite system.Then the type of interaction between soy protein isolate and chitosan in solution was studied with spectroscopy.The main research contents and results are as follows:(1)In pH3,the complex turbidity changes little with the addition of chitosan because there are considerable positive charge on the two macromoleculars so that there are eletrostatic repulsion between the two compounds.In pH4 and pH5,low concentration of chitosan solution will not change the turbidity value while a high concentration of chitosan can reduce turbidity value of the composite solution.This is because the chitosan with positive charge could generate electrostatic force with part of the negative charge on the surface of soy protein isolate near the isoelectric point.In pH6,a high concentration of chitosan can obviously increase the turbidity value of compound solution,due to the electrostatic force is strongest so that it produce larger complexes.In pH7,low concentration of chitosan had weak effects on the turbidity value of compound solution while a high concentration of chitosan can reduce the turbidity value of compound solution.(2)In pH3,adding the chitosan didn't make the average particle of compound solution bigger,when the proportion is 1:30,a peak of chitosan appeared and solution potential value is positive.In pH4 and pH5,due to the solubility,the average particle is too big,the addition of chitosan make average particle size increases slightly,and potential value is always positive.In pH6 and pH7,the average particle size also has a tendency to increase,potential value increased from-10.0 mV and-11.9 mV to 34.3 mV and 33.6 mV,respectively.(3)In pH 3-7,with the increase of chitosan,the viscosity of compound solution are increasing,This is mainly because the largest contribution of chitosan to the viscosity of the whole solution,But by comparing the different pH of composite solution viscosity under same proportion we can find that in pH6,compound solution have the greatest viscosity because electrostatic force is the strongest between soy protein isolate and chitosan.(4)By Isothermal Titration Calorimetry(ITC)technology we can get the thermodynamic properties of soy protein isolate and that of chitosan under different pH.In pH3,the heat change between the two in the process of titration basically is zero,this is because both the soy protein isolate and chitosan had a lot of positive charge so that their interaction force is very weak,In pH6,however,the first drop of heat change is 787.99 J/mol,titration end point appeared about in the 16th drop,and the heat change at this time is 16.66 J/mol,probably due the soy protein isolate during pH6 appeared with negative charged while chitosan with positive charge,and they get together due to electrostatic forces.(5)Spectroscopy analysis on the interaction of soy protein isolate and chitosan,to study the interaction between soy protein isolate and chitosan by using fluorescence spectroscopy,ultraviolet-visible absorption spectroscopy and Fourier transform infrared spectroscopy(FT-IR),the paper mainly discusses the chitosan impact on the fluorescence spectrum of soy protein isolate.The fluorescence quenching of soy protein isolate by chitosan discussed to study the types of interaction between the two.Through the fluorescence spectrometry analysis,it turned out that fluorescence quenching of soy protein isolate by chitosan is static quenching,and the main force between the two is the electrostatic force,the ultraviolet-visible absorption spectrum of soy protein isolate by chitosan also produced some influence,but the position of ultraviolet absorption peak has not changed,but the absorption value is increased,through the Fourier transform infrared(FT-IR)spectrum analysis on the composite condensation of soy protein isolate and chitosan,the interaction between the two is also the electrostatic force.