| Rice resources is abundant in China and protein in rice is rich.The rice protein has the advantages of reasonable amino acid composition and high nutritional value.But in the processing of rice,these proteins resources were often been wasted.The low solubility of rice protein is the main reason,which affected the other functional properties and has been restricted in the production and processing of food.Therefore,it is necessary to modify the rice protein,improve its functional properties,and make it used in food.In this paper,firstly,rice protein was modified by high pressure homogenization process,and the changes of functional properties and structural characteristics of rice protein in high pressure homogenization process were studied;Secondly,the process of enzymatic hydrolysis of rice protein by alkaline protease was studied;Finally,on the basis of enzymatic hydrolysis,the functional properties and structural characteristics of rice protein hydrolysate were studied by high pressure homogenization and enzyme modified rice protein,and the specific results were as follows:(1)The effects of high pressure homogenization treatment on the functional properties of rice protein was studied.Choose the concentration of rice protein:2%,4% and 6%,and the homogenization pressure:5MPa,40 MPa,80MPa,120 MPa,which studied that different pressure had an effect on the functional properties of different concentration of rice protein.The results showed that high pressure homogenization can improve the solubility of rice protein,and the low concentration which was 2% solubility was best,and solubility can reach 75.26?g/mL in 120 MPa,compared to the sample without the homogenization,it increased by 154%;Foaming activity did not have very obvious improvement by high pressure homogenization,only the concentration of 4% and 6% whose foaming activity reached the highest at 5MPa and 80 MPa,respectively,154% and 167%,and,compared to the sample without homogenization treatment,it increased by 4.76% and 9.15%,respectively;But foaming stability of rice protein solution of each concentration was improved,and foaming stability of low concentration of 2% was the most significant;Emulsifying activity index of the rice protein whose concentration of 2% increased first and then decreased,and reached maximum in 5MPa,that was 11.31m2/g,compared to the samples without homogenization treatment,increased by 27%;When the concentration of4% and 6%,emulsifying activity increased,respectively in 80 MPa and 120 MPa reached maximum,that were 14.82m2/g and 13.35m2/g,compared to the samples without thehomogenization,and increased by 26% and 27%;Emulsifying stability index that the concentration of 2% and 6% increased first and then decreased,and reached maximum,95.83 min and 45.40 min in 40 MPa and 80 MPa,compared to control sample,it increased by122% and 120%,respectively,but emulsion stability index decreased when the concentration was 4%;The viscosity of rice protein solution in each concentration reached the maximum in 120 MPa.(2)The effects of high pressure homogenization treatment on the structural properties of rice protein was studied.Selected the intermediate concentration of rice protein was 4% as the research object,the changes of the particle size,the chemical reaction,the content of the sulfhydryl and the disulfide bond,the surface hydrophobicity index and the subunit structure were studied.The results showed that with the increasing of pressure,the specific surface area inceased,surface area average particle size decreased,chemical interaction(ionic bonds,hydrogen bonds,hydrophobic interactions)changed;The content of sulfhydryl decreased and the content of disulfide bond increased;the surface hydrophobicity index increased.These suggested that the three dimensionalstructure of rice protein was affected by high pressure homogenization.But the subunits of rice protein was not affected by high pressure homogenization.(3)Rice protein was modified by Alkaline protease which improved its dissolution rate.On the basis of single factor experiment,the value of pH about enzymatic hydrolysis was 8.0,the rice protein dissolution rate was used as the index.The effect factors of enzymatic hydrolysis time,enzymatic hydrolysis temperature,substrate concentration and enzyme addition amount on the dissolution rate of rice protein were investigated,and the test of four factors and three levels-L9(34)orthogonal was designed.The best combination was that the enzymatic hydrolysis time was 45 min,the enzymatic hydrolysis temperature was 55?,the substrate concentration was 6% and the enzyme concentration was 1500U/g,the results showed the rice protein dissolution rate was 11.40%±0.13%,verified as 11.47%±0.13%.Meanwhile established Michaelis Menten equation,the maximum reaction rate was got and the value was 0.345mg/min·ml;when the substrate concentration is 114.92mg/mL meaned 11.49%,the reaction rate was the half of the maximum reaction rate.(4)Under the best combination of the enzymatic hydrolysis,compared enzymatic hydrolysis with high pressure homogenization combined with enzymatic hydrolysis to modify dissolution rate of rice protein,the properties of functional and the structure of hydrolysates of rice protein were studied.The results showed that the solubility and foaming stability,emulsibility,water holding capacity and oil holding capacity wereimproved,while the foaming activity was not improved.(5)The effects of Enzymatic hydrolysis process on structure properties of rice protein.compared to the protein without enzymatic hydrolysis,the content of sulfhydryl of enzymatic hydrolysates decreased,surface hydrophobicity index decreased.SDS-PAGE analysis showed that enzymatic hydrolysis made rice protein dissociated. |
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