Study On Purification And Modification Of Rice Protein From Rice Dreg

In this paper, the preparation of rice protein from rice dreg, the reason of insolubility, structure characteristics and modification of protein were systematically investigated so as to obtain high purity protein and improve its applicable properties.The preparation condition were systematically investigated. The result showed that defatting with sugar ester was feasible and the protein content of the product manufactured by amylase and cellulose hydrolysis after defatting was 86%.The fat content of the product was 2.64%, closed to that defatted with hexane.Based on the problem in the progress of protein preparation, the character between protein and sugar was investigated. The research by Gel chromatography proved rice dreg and rice protein from rice dreg to be sugar-protein complex. The result of SDS-PAGE showed that 36KDa was the complex. But sugar quantity in rice dreg protein was higher than that in rice dreg and rice protein.β-elimination reaction revealed that glycoprotein was not O-glycoside peptide bond. The existence of complex was the reason why we can not remove all the sugar in rice dreg.The effect of liquefaction treatment on starch at high temperature on rice protein was investigated. Results demonstrated that at the beginning of liquefying at high temperature leaded to the evident loss of albumin, globulin, prolamin and glutelin, the increase of insoluble protein,content of amino acid and hydrophobic value.As the time went on, albumin, globulin and prolamin decreased relatively slowly。The content of amino acid reduced . Amino acid analysis showed that some protein nitrogen transformed into nonprotein nitrogen during the progress of liguefaction. All the result above showed that protein degenerated seriously.Gel chromatography and UV spectra showed the differences in whole molecular, but homology in their sub-compositions between rice dreg protein and rice protein .The subunit composition of the protein was researched with SDS-PAGE, Four subunit ( mainly 13KDa and 36KDa) were found in rice dreg protein and five in rice protein. The amino acid analysis showed that there were more Cys and less Lys in rice dreg protein than that in rice protein. CD spectra also indicated the evident differences between rice dreg protein and rice protein. The carbonyl levels in rice dreg protein are significantly higher than that in the rice protein. It indicated that amino acid residue side chains of rice dreg protein had been oxidated.In order to dissolve the rice protein and improve its physicochemical properties, the method of enzymatic hydrolysis pretreated with hot-press was investigated. The result showed that the efficiency of hydrolysis pretreated with hot-press was better than that unpretreated. After treated for 5min on the condition of 120℃and 0.1MPa and then hydrolyzed with Trypsin ,the soluble protein was 62% and the purity was 90%.The solubility, emulsification and foam activity were improved after modification.