Research On The Phase Separation Of Soluble Rice Protein-non-adsorbed Polysaccharide Composite System

Rice is a major staple grain in the world, and its protein content is about 8～13%. It has high nutrition, hypoallergenic, healthy edible and other traits. However, the low solubility of rice and it cannot form visco-elastic network-like structure after gel process limits its application in industrial and food products. The interaction of proteins and polysaccharides relate to the uniformity, texture and oral feel of products. Many food scientists studied the interaction of protein and polysaccharide in order to obtain the appropriate control and design of the new products with good quality and structure. In present study, phase diagram, confocal laser scanning microscopy and dynamic modulus test were used to systematically study phase behavior, rheological properties and microscopic changes of soluble rice protein-polysaccharide mixed systems.The main conclusions were as follows:(1) The structures of soluble rice protein were characterized. Two kinds of soluble rice protein were produced by enzymatic deamidation. Size-exclusion high-performance liquid chromatography (SEC-HPLC) tests showed that the deamidated process made the depolymerization of rice protein. Intermediate aggregate was reduced and small molecules did not produce. The dynamic and static laser light scattering technique investigated the hydrodynamics radius of soluble rice protein A and B, which were 182.7 and 131.0, respectively. Zeta potential of rice protein A was-26.2, and that of protein B was-12.6. The results showed that deamidation was helpful for the improvement of the increase of protein solubility and functional properties. After modification the viscosity of rice protein was significantly decreased, and the viscosity of rice protein A and B were 10.5 and 8.0, respectively. Scanning electron microscope(SEM) results revealed the microstructures of rice proteins. Native protein network structure was filled with carbohydrate. While the skeleton structure of deamidated protein samples was exposed, and the network structure of protein A was combined closely.(2) The phase separation of soluble rice protein-carrageenan mixed system were studied. Phase diagrams of mixed system showed the formation of homogeneous, phase separation and gel area. And the results indicated that for two different kinds of soluble protein, the smaller the size of biopolymer was, the higher concentration of phase boundary it had. The microstructures of three kinds of composite system were observed by Confocal laser scanning microscope (CLSM). The difference of size of protein led to the differences of phase diagrams and microstructures of the composite system. The test of the dynamic modulus of three kinds of hybrid system further validated the phase diagram and CLSM observation. The study proved that the larger size of the soluble rice protein promoted the phase separation with carrageenan, and demonstrated that rice protein and carrageenan phase separation was mainly due to the depletion interactions.(3) The phase separation of soluble rice protein-dextran mixed system were studied. Within the scope of experimental concentration, only the homogeneous area and phase separation area of the composite system were investigated. Compared to the interaction of protein with carrageenan, thermodynamic incompatibility of carrageenan with soluble rice protein was stronger and incompatibility areas were larger. The CLSM observation found the visibly differences of microstructures for two kinds of rice protein/dextran composite system. The results of microstructure proved the phase separation occurred and further demonstrated that the phase separation of rice protein and soluble neutral polysaccharide-dextran was due to the effect of emptying of the dextran chains, made effective and uneven cross-linking in protein-rich areas. The increase of size of rice protein particle promoted the phase separation between them. Dynamic modulus of the mixed system were determined:the viscous modulus and elastic modulus of system were increased with the increasing of frequency. The above results indicated that when rice protein and soluble dextran concentrations were low, composite system was flow; and the increase of concentration of protein or dextran revealed the formation of gel network structure.