Study On The Changes Of Structure And Functional Properties Of Rice Bran Protein During Storage And Stabilization Of Rice Bran

The rice bran resource is very abundant in China, the annual output reached 14 million tons in recent years. Rice bran with 14～24%oil,12～18% protein is a high quality resource for the preparation of rice bran oil (RBO) and rice bran protein (RBP). Rice bran contains strong activity lipase and lipoxygenase, and easy cause hydrolysis of lipid to form free fatty acids (FFA), leading to rice bran rancidity. FFA further oxidized to release free radicals and reactive oxidation products which resulted in RBP oxidation. The changes of structure, functional properties and enzymatic properties of RBP during storage and stabilization of rice bran were studied in this paper.Fresh rice bran which stored in a condition for different period were used as material to prepare RBP after defatting, and changes of oxidation degree and structure of RBP during rice bran storage were investigated by protein carbonyl content, free sulphydryl and total sulphydryl content, fourier transform infrared spectrometer, intrinsic fluorescence, surface hydrophobicity, size, Zeta potential, size exclusion chromatogram, and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The results indicated that acid value and peroxide value of rice bran curde oil, carbonyl content, disulfide content, β-turn and random content, size of RBP increased as storage time of rice bran increased, free sulphydryl content, α-helix and β-sheet content, intrinsic fluorescence intensity, surface hydrophobicity, and absolute value of Zeta potential of RBP decreased as storage time of rice bran increased, blue shift of wavelength of the maximum emission was accompanied by formation of oxidation aggregates which involved in disulphide bonds and non-disulphide covalent.Storage of rice bran had significantly changed the functional properties of RBP. The changes of functional properties of RBP during storage of rice bran were investigated by solubility, water holding capacity, oil holding capacity, foaming capacity, foaming stability, emulsion activity, emulsion stability, rheological property. The results indicated that solubility, gel strength of RBP decreased, water holding capacity, oil holding capacity, foaming capacity, foaming stability, emulsion activity, emulsion stability of RBP firstly increased and than decreased as storage time of rice bran increased.Twin screw extrusion stabilization for rice bran which stored in different period exacerbated the oxidation degree of RBP during rice bran storage. Fresh rice bran firstly stored in a condition for different period and then stabilized by twin screw extrusion technique were used to prepare RBP after defatting, changes of oxidation degree, structure and functional properties of RBP was also studied. The results indicated that oxidation degree of RBP were significantly exacerbated after stabilization, changes of structure and functional properties of RBP were more significant, depolymerization of subunit formation from RBP oxide aggregates as storage time increased.Storage of rice bran had significantly changed the enzymatic properties of rice bran protein hydrolystates (RBPHs). Properties of RBPHs by enzymolysis using alkaline protease for RBP which prepared by rice bran firstly stored and then stabilized were investigated, the results indicated that ABTS free radical scavenging activity, DPPH free radical scavenging activity, superoxide (O2-·) scavenging activity, radicals hydroxyl (·OH) scavenging activity and metal chelating ability of enzymatic product of RBP firstly increased and than decreased, and reduction ability still decreased as protein oxidation of RBP increased.