Modification And Thermal Aggregation Of Rice Glutelin And Its Gel Properties And Applications

Broken rice is a by-product produced during the rice milling process.Its nutrients are similar to whole rice,but its price is less than half of that of whole rice.Broken rice is mostly used for animal feed,which not only reduces the value of goods,but also causes a waste of rice resources.The protein in broken rice is high,and it has the advantages of high nutritional value and low allergy,but its low solubility limits its application in the food industry.In this thesis,rice glutelin(RG)is prepared by using alkaline extraction and acid precipitation method with broken rice as the raw material.Sodium tripolyphosphate was selected as a phosphorylation agent to phosphorylate rice glutelin(PPRG),and the structural,functional and thermal characteristics of phosphorylated rice glutelin were studied.In addition,rice glutelin before and after phosphorylation modification were heated for different time to study the structural,physicochemical properties and interactions of the protein during heating.Then the effects of phosphorylation modification and thermal pre-aggregation on the gelation properties of rice glutelin were explored.Finally,riboflavin was encapsulated with phosphorylated rice glutelin gel as an encapsulant,and the encapsulation efficiency,storage stability and simulated release in the gastrointestinal tract of riboflavin were investigated.Firstly,the effects of sodium tripolyphosphate modification on the structural,functional and rheological properties of rice glutelin were studied.The results showed that the phosphorylated rice glutelin samples had a smaller particle size and a higher absolute value of zeta potential.Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy proved that the-OH and-NH₂groups of rice glutelin and the sodium tripolyphosphate were connected through C-O-P and C-N-P groups.The microstructure results showed that the surface of the phosphorylated rice glutelin sample became very rough.In addition,the solubility,emulsification,foaming,thermal stability,and apparent viscosity of the phosphorylated rice glutelin samples were significantly improved.The rheological properties showed that phosphorylation modification can improve the viscoelasticity of rice glutelin.Secondly,native rice glutelin and phosphorylated rice glutelin were heated for 15,30and 45 min,respectively,and the effects of different heating time on the structural,interaction and rheological properties of phosphorylated rice glutelin were studied.The results showed that the turbidity of the PPRG samples after heating is higher than that of the RG samples.The particle size distribution results showed that after heating for 45min,protein aggregates of 1000-1500 nm were formed.The changes in protein structure indicated that the protein would unfold after a short time of heating,and aggregation occurred when the heating time was extended to 45 min.In addition,after heating for 45min,the microstructure of the PPRG samples became dense and compact.Rheological analysis showed that phosphorylation modification and heat treatment can improve the viscoelasticity of RG.In addition,the effects of phosphorylation modification and thermal pre-aggregation on the structural,gelation and microstructural of rice glutelin gel were studied.Phosphorylation modification and thermal pre-aggregation treatment significantly improved the storage modulus(G')and loss modulus(G")of the RG gel,as well as the gel strength and water holding capacity.SDS-PAGE electrophoresis results showed that more protein was degraded in the gel formed by thermal pre-aggregation,indicating that more interactions occurred in the protein molecules;the molecular forces analysis showed that the major interactions involved in the formation of gels were hydrophobic interactions and disulfide bonds;Scanning electron microscopy and Confocal laser scanning microscopy showed that the gels formed by thermal pre-aggregation had stronger interactions and denser network structures,while the gels formed by direct heating were rougher.Finally,the application of phosphorylated rice glutelin gel embedding riboflavin was studied.The efficiency of gel-encapsulating riboflavin prepared by phosphorylated rice glutelin was>95%,and the riboflavin loss rate was<16%after 4 weeks of storage.In addition,the swelling properties of the gels prepared by phosphorylated rice glutelin decreased,and with the increase of the degree of phosphorylation,the release rate of riboflavin in rice glutelin gel in simulated gastrointestinal fluid was significantly reduced.Therefore,the gel prepared by phosphorylated rice glutelin had a sustained release effect on the controlled release of riboflavin.In this thesis,phosphorylation modification of rice glutelin was carried out,it was found that the modification of sodium tripolyphosphate significantly improved the functional properties and thermal aggregation of rice glutelin,and the gel properties of rice glutelin were also improved.Finally,the prepared rice glutelin gels were used to encapsulate riboflavin,and the results showed that the phosphorylated rice glutelin gel had better encapsulation efficiency.Therefore,phosphorylation modification is beneficial to improve the functional properties of rice glutelin,thereby broadening the application of rice glutelin in the food industry.