| Rice protein was grafted with dextran by microwave radiation through Maillard reaction. In order to improve the value of the rice protein for application, the conditions for grafting, the structure and functional properties of the rice protein-dextran grafts were studied in system. It was tried to use spay drying to prepare the powder of the grafts.The raw material of rice protein was extracted by alkali (purification about 90%). The conditions affecting the degree of graft reaction were studied, such as the power of the microwave, the temperature of the reaction, pH of the solution, the concentration of protein and the ratio of protein to dextran. Response surface design and analysis were finished by SAS software to optimize the technique. When the maximum degree reached 48.1%, the optimized condition was as follows: the ratio of protein to dextran was 1:6, the concentration of protein was 4.03mg/mL and the reaction time was 22min.The functionalities such as solubility, emulsifying ability, foaming ability and heating stability were determined at different degree of graft (DG) which showed that the functionality of the grafts can be greatly changed by the reaction. And the optimize DG of each functionality was various. When the DG ranges from 0 to 46.4%, the solubility of the grafts was gradually improved with the DG, and also in the pH range of 3 to 11, the grafts were markedly better than that of the rice protein. The most suitable DG for emulsifying ability was 26.7% but18.0% for foaming ability, while the higher the DG was, the more stable the emulsifying stability became, which the same as foaming stability. The rice protein and grafts were heated for 30min from 60 to 95oC in solution at pH5,7 and 9, respectively, and the heating stability kept well.The structure of the rice protein and its grafts was analysed, and the mechanism was primarily discussed also. After graft reaction, argine and lysine were apparently decreased, especially argine. It was agreed with the Maillard reaction mechanism. The free amino groups in side chains of protein took part in the reaction and form the covalent band. According to the analysis of SDS-PAGE, the new bands of the grafts subunits were closer to the upper of separating gel, and the bands about 15,000 and 20,000 disappeared. The HPLC and gel chromatography in Sepharose-CL-6B of the grafts both illustrated that after grafting the molecular weight of the grafts became larger. The FTIR analysis of the pure sample showed the same conclusion that dextran was grafted to rice protein by covalent band, leading to increase the molecular weight of the protein subunit, but not protein aggregation.The rice protein aggregation was dispersed after grafting and clung on the pieces formed by the dextran on the photos from scanning electron microscope (SEM). The result of dynamic light scattering (DLS) showed the state of grafts in solution that the particle size distribution was narrower than that of the rice protein and the average size was larger.Spray-drying cost less and was more suitable for continous production process when compared with freeze-drying. The results showed that the buff powder made by spray drying was small and well-proportioned, but the functionalities such as solubility and foaming ability were a little lower.
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