Preparation And Characterization Of Soybean Protein/Polysaccharide Composite Gels Slow-release System

In recent years,the application of encapsulation,protection and delivery of water-soluble bioactive compounds and drugs has attracted widespread attention in the food and pharmaceutical industries.It is necessary to develop an economical and efficient delivery system for water-soluble substances.In this thesis,?-carrageenan(KC),soy protein isolate(SPI),and konjac glucomannan(KGM)were used as raw materials to prepare hydrogels,which was effective in slowing down the release rate of water-soluble substances during in-vitro digestion.The properties of composite gels,the release mechanism of the core material in gels,and the interaction between protein and polysaccharide were investigated.Firstly,SPI/KC composite gels were prepared with KC and SPI as raw materials.Monascus yellow is a water-soluble pigment with high stability,bright color and easy detectability.Therefore,the digestion and slow-release properties of the composite hydrogels were tested using monascus yellow.The results of texture and rheology showed that the hardness and cohesiveness of the composite gels were increased with the increase of SPI concentration.The addition of KCl could accelerate the gels' formation and the hardness of gels was increased,but the cohesiveness and stability of the formed gels were decreased.The lowfield NMR analysis results showed that the bound stability of water molecules was increased enhanced with the increase of SPI concentration.The microstructure was observed using atomic force microscopy,which revealed that the addition of SPI made the gel structure more uniform and compact,and the addition of KCl promoted the formation of gels but the compactness of gels was slightly reduced.The in-vitro digestion results showed that the initial release ratio of monascus yellow in the pure KC gel was about 30%,and the cumulative release ratio at the end of the simulated gastric juice digestion was close to 90%.The SPI/KC composite gels could effectively slow down the release of monascus yellow,and the optimum concentration of SPI and KCl were 6% and 0%,respectively.Under this condition,the initial release ratio of monascus yellow was only 5.65%,and the cumulative release ratio in the gastric and intestinal digestion stages were 37.09% and 97.18%,respectively.In order to further improve the properties and slow-release effect of the composite gels,KGM was used to prepare the SPI/KC/KGM composite gel.The texture results showed that the addition of KGM increased the hardness of the composite gels,but the springiness and cohesiveness were decreased.The results of rheology and scanning electron microscopy showed that proper addition of KGM could improve the rigidity and compactness of the gels,but it would have an adverse effect when the proportion of KGM was too large.The in-vitro digestion results showed that when the ratio of KC/KGM was 9:1,the composite hydrogel had the best slow-release effect on glucose.Under this condition,the initial release rate was 10.38%.In addition,the cumulative release rates in simulated gastric and intestinal juices were 36.17%and 85.79%,respectively,which were reduced by about 3% and 6% respectively compared with SPI/KC composite hydrogel.Ritger-Peppas model was used to simulate the release rate of the core material in the digestion process and the release mechanism of the core material in the composite gels was elucidated.The analysis results showed that during the process of simulated gastric digestion,the release mechanism of core materials in the composite gels was Fickian diffusion.However,the release of core materials in the simulated intestinal fluid followed irregular diffusion pattern.The interactions between KC,SPI and KGM were investigated by electrophoresis analysis and Fourier transform infrared spectroscopy(FTIR).Electrophoresis results showed that the composition of SPI did not change,and there was no chemical crosslinking between proteins and polysaccharides.FTIR results showed that the characteristic absorption peaks of the freezedried composite gels powder and the physical mixture powder were similar,and no specific absorption peaks appeared or disappeared,which indicated that the composite gels were physical gels and the interactions between proteins and polysaccharides were mainly noncovalent interactions.Furthermore,the main aggregation forces among gel molecules were analyzed by measuring the change of the hardness of gels before and after adding denaturing agents(Na Cl,urea and SDS).The molecular aggregation force of the composite gel system was mainly electrostatic interaction,while hydrophobic interaction and hydrogen bond interaction were relatively weak.