Studies On The Extraction And Purification Of Rice Protein

China’s rice resource is the most rich in the world. The annual output is about 200million tons. The byproduct broken rice from rice processing account for 10% to 30% ismainly for the production of starch sugar, MSG and wine. The use of rice slag from thebyproduct of starch sugar production has been a major difficult problem to enterprises. In thepast, we failed to make full use of it reasonably, which was used as animal feed, so resulted inserious waste of resources. Rice slag is extremely good raw material for extraction of riceprotein, whose protein is more than 40%. We can recycle the protein from the rice and use itreasonable, this can not only bring plentiful protein for human being, eliminate the negativeinfluence of starch production, but also improve the level of rice processing and additionalvalue of the byproduct. All of this has important social and economic significance.Rice protein is recognized as high quality edible protein, its biological potency is high,the antigenicity is low, rice protein won’t bring allergic reaction. In all the grain, rice is theonly one free from allergy testing. So rice protein is considered to be a high developmentvalue plant proteins resources, get the attention of researchers around the world. The thoroughunderstanding of rice protein molecules composition, structure and nature will be the first stepto develop and utilize rice protein rationally, its structural analysis and evaluation functionneed to acquire high purity rice protein. So separation and purification of rice protein becamethe necessary link of further development.Using long-shaped rice as material, my research studies the components of rice protein indetail. We apply Osborne classic methods to purify four kinds of protein including albumin,globulin, glutenin and gliadin. As a result, the content of glutenin(84.09%) is much higherthan albumin(3.04%), globulin(9.38%) and gliadin(3.49%). Using SDS-PAGE to analyzethese four proteins, the result of the study show that: the molecular weight (MW) of albuminis around 59.8 kDa, 42.4 kDa, 16.2 kDa. The MW of globulin is 55.2~53.8 kDa, 25.9~23.4kDa, 20.2~17.9 kDa, 16.5 kDa. The mainly MW of gliadin is 16.8~14.5 kDa. According tothe distribution scope of MW, the glutenin can be divided into six regions obviously: 54.6kDa, 38.4~37.1 kDa, 36.3~34.2 kDa, 25.9~24.1 kDa, 22.2~21.4 kDa, 16.3~14.9 kDa. Soglutenin is relatively complex. According to the distribution characteristics of four protein components in rice, wedecide to use the method of alkali extraction and acid precipitation to prepare the protein forfollowing study. Based on earlier study, the method of extraction is as follows: the rice passthrough 120 mesh sieve is extracted for 2 hours at normal temperature with 0.05 M alkalisolution which is 10 times as the rice powder weighs. In this condition, the extraction ratio ofprotein is about 73.89%. The extraction contains 87.90% protein. The solubility of the proteinis less than as 5% when pH is between 5 and 8, when the pH is around 11, the solubility ofrice protein rapidly increased, when is 12.5, the solubility becomes 85.17%. In this paper,high performance liquid chromatographic was used to determine the molecular weightdistribution of homemade rice protein in the different dissolution conditions, we found thatrice protein were not completely dissolved in various solvents, there are differences indissolved part. Change of the pH (pH<3，pH>10) or adding SDS to improve the solubility ofrice protein was beneficial to the dissolution of the high molecular weight protein.In order to translate lab achievements into real productive forces, based on the previousstudies, we set up a pilot production line. Using the method of alkali extraction and acidprecipitation, we had produced rice protein products meeting the enterprise standard, Thepilot-plant Enlargem of the rice protein extraction has completed. At present, we already canproduce the protein powder whose protein content is 85% or more, achieving the expectedtest.After preliminary separation of alkali extraction and acid precipitation we can getglutelin, which is still complex and need further separation and purification. Through researchthe solubility of the lab homemade rice protein, we found that: when pH between 3 and 10,the solubility of glutelin is all under 10%, so protein’s bad solubility become the maindifficulty for its separation and purification. This paper have explored IEC and GFC toseparate and purify the rice protein, alkali mention rice protein was dissolved inNa2HPO4-NaOH (pH12.50, 0.05 mol/L), by using DEAE Sepharose Fast Flow ion exchangechromatography for rice protein separation with stepwise elution, 0.10 mol/L, 0.25 mol/L,0.40 mol/L and 0.55 mol/L salt buffer was used to elute the medium. Alkaline extraction ofrice protein was separated primarily. Three elution peaks F1, F2, and F3 were obtained. Inthis system, proteins dissolved more completely. The use of salt solutions of different concentrations, initial separation and purification of rice protein by the electric chargestrength from small to large is feasible. F3 is collected for the gel filtrationchromatography.Four elution peaks F3-a,F3-b,F3-c,F3-d were obtained.The HPLC of F3-dcomponent showed its relative molecular mass is 38 048 Da, its purity is 91.14%.