| Tikitiki (rice bran) make up about 6% to 8%of rice. China is enriched with rice bran resources, but only 10%～15%of them are utilized efficiently. The Chinese food industry "twelfth five-year" development plan proposed that attention should be focused on the utilization of rice bran, by producing rice bran oil, rice bran protein, oryzanol, rice bran wax, inositol and some other productions. Rice bran contains about 12%～16% proteins. Due to the complexity of its solubility, the compositive utilization of rice bran is still non-fulfilled. In rice bran, as Osborae’s classified way, the account of albumin, globulin, prolamin, and glutelin are 37%,31%,2%, and 27% respectively, and this makes it difficult to find a proper extracting method for the four components. In the present research, a compound alkali-enzyme extracting method was used to extract rice bran protein, and then the proteins in the extractions were separated and purified. We got a high extraction and high purification rate of rice bran protein, which laied a theoretical foundation for industrialized production.In this research, we used the alkali method to extract most of the protein from defatted rice bran. After the single factor test and the orthogonal experiment method, we got the optimum conditions for the alkali extraction:pH 11, reaction temperature 60℃, the ratio of liquor to solid 12, and the reaction time 2.5 hour. Under this condition, the extraction rate could reach at 73.41%. Howere, after extracted by alkali method, there was still about one quarter of protein left in the residue. Then phytase, cellulase, and lipase were further used to extract residue protein. Our results showed that the extraction rates of these enzymes were 24.58%,42.68%, and 26.39%, respectively. Among them the lipase supplied the best extracting efficiency. Moreover, after the single factor and responding surface tests optimized the technological conditions of the lipase extraction, the optimal process conditions were found to be at pH 7.5, the reaction time 2.5 hour, and the amont of enzyme 597.35 U/g protein. Under this condition, the extraction rate of the rice bran residue protein was 45.58%. After extracted by alkali and lipase, the total extraction rate of rice bran protein was 84.80%, which increase by about 10%. The rice bran protein extracted by alkali-enzyme was tested for their basic properties and functional properties. As far as molecular weight of the proteins be concerned,60.20%was above 10,000 Da,9.75%was among 5,000～10,000 Da,13.46% was among 180-5,000 Da, and 16.59% was below 180 Da. The solubility, emulsiflcation, emulsion stability, and foaming ability of it increased as the pH increased, and when the pH was lower or higher than its p, and the foam stability reached the highest point at its pi. When pH is 7, the volume denstity of the rice bran was 0.51, water-absorbing quality was 3.63, oil-absorbing quality was 2.46, solubility ability was 61.93%, emulsification was 0.46, emulsion stability was 39.32%, foaming ability was 107.49%, and foam stability was 60.84%.Amylase and cellulase were then used to preliminarily purify the rice bran protein. Amylase showed fairly better purifying efficiency and it could increase the protein purification rate from 62.35% to 72.02%. After amylase treated, we got preliminary purification protein (PPRBP). Then IEC was explored to separate and purify the PPRBP, by using DEAE Sepharose Fast Flow ion exchange chromatography. The PPRBP was dissolved in 0.05 mol/L Tris-Hcl buffer, with gradient elution of 0 to 1 mol/L NaCl Tris-Hcl buffer, and three elution peaks A, B, and C were obtained. A was analyzed to be an alkalescence or neutral protein with positive charge, and B and C were acid-stage protein with negative charge. Finally, peaks B and C were collected and dried after dialyzed, the protein contents of them were verified to be 77.86% and 87.58% respectively. This help us to get the conclusion that purity of rice bran protein was improved by this two-step methods. |
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