Studies On The Extraction And Modification Of Rice Protein

The quantity of sulfhydryl of rice protein increased during the rice storage because of the transformation of–SH to -S-S-, which led to the changes of protein conformation and increases of protein sedimentation coefficient and average molecular weight, also led the decrease of the protein extractability. Moreover, the major storage protein of rice is glutelin (about 80%). The insolubility of it restricted the further application of rice protein.Based on properties of aged indica rice, this thesis systematically studied the extraction of rice protein using reductant-alkali solution and its enzymatic and chemical modification. The aim is to obtain higher extractability and improved solubility, and expand the applications of rice proteins on various types of food.This thesis used reductant-alkali solution to extract rice protein in order to obtain higher extractability. Sodium sulfite and dithiothreitol, which reduced the disulfide to sulfhydryl, were used during the extraction. The best extraction process and condion were: 0.05 mol/L NaOH, 0.50% Na2SO3, 2.5% dithiothreitol. The solid-liquid ratio was 1: 12 at 35℃for 4h. The rice protein extraction rate was 95.26%. Compared to the traditional alkali extraction process, the present method increased the extraction rate, protected the rice starch, and reduced the alkali concentration i.e. reduced the damage to the environment.Enzymatic modification and reducing agent-acid methods were used to improve the solubility of rice protein. Trypsin was selected. This thesis investigated the concentration of trpsin, concentration of rice protein and enzymatic reaction time on the solubility and degree of dydrolysis, and determined the optimum enzymatic process and condition: 5.00% trypsin, 3.00% rice protein, at 50℃, pH 8.0 for 2.5h. The solubility of rice protein hydrolysates was 83.65 %, and degree of hydrolysis was 2.87% under such a condition. The results of HPLC showed that relative molecular weight of rice protein decreased significantly after trypsin modification. Rice protein was dissociated to some small peptides, thus the solubility of rice protein was improved.Reducing agent (dithiothreitol, DTT)-acid (hydrochloric acid) modification was also used for rice protein modification. The concentration of hydrochloric acid, rice protein and DTT, reaction temperature and time affected the solubility of rice protein hydrolysates and degree of hydrolysis. The optimum process and conditions of reducing agent-acid modification were as follows: 0.60 mol/L hydrochloric acid, 2.50 % rice protein, 0.60% dithiothreitols, at 90℃for 2.0 h. The solubility of rice protein hydrolysates was 95.37%, and degree of hydrolysis was 5.21% under such a condition. Compared to the traditional acid modification, the present method improved the solubility of hydrolysates of rice protein under neutral aqueous solution, enhanced efficiency of rice protein modification, reduced the acid concentration, decreased the cost of production and protected the environment. The results of HPLC showed that the degree of hydrolysis was lower after reducing agent-acid modification compared to trypsin modification, and the resultant systems were composed of some subunits of rice protein and some small peptides.