Studies On Extraction Of Rice Bran Protein And Its Antioxidative Peptides

Fresh rice bran, expanded rice bran and defatted rice bran were used to extractrice bran protein by three kinds of chemical methods. The yield of protein in rice branextracted was a key index. The material-liquid ratio, pH value, extraction time,temperature, salt concentration for each steps of three methods were determined byorthogonal experiments. Then, the rice bran peptides were prepared, isolated andpurified, and the effect of their antioxidant activities were determined. The resultsshowed as follow:1. The results from the alkali method indicated that the optimal technologies offresh rice bran extracted were2.5h, pH11,45℃and material-liquid ratio of1:11,and the yield of protein was34.49%; the optimal parameters of expanded rice branextracted were2.5h, pH12,50℃and material-liquid ratio of1:9, the yield ofprotein was25.44%; the optimal parameters of defatted rice bran extracted were3h,pH13,35℃and material-liquid ratio of1:9, and the yield of protein was24.3%. Forthe acid method used, the optimal extraction parameters of fresh rice bran were3h,pH0.5,35℃and material-liquid ratio of1:11, and the yield of protein was25.88％;the best extraction technologies of expanded rice bran were3.5h, pH0.5,35℃andmaterial-liquid ratio of1:10, and the best yield of protein was23.64%, the bestextraction parameters of defatted rice bran were3.5h, pH0.5,40℃andmaterial-liquid ratio of1:8, and the best yield of protein was18.18％. For the saltextraction method used, the optimal NaCl level, temperature, material-liquid ratio offresh rice bran were respectively0.6mol/L,35℃and1:11, and the extraction ratewas15.66%; the best NaCl level, temperature, material-liquid ratio of expanded ricebran were respectively0.4mol/L,40℃and1:11, and the extraction rate was15.55%;the optimal NaCl level, temperature, material-liquid ratio of defatted rice bran wererespectively0.6mol/L,40℃and1:8, and the yield of protein was7.86%. For the totalyield of protein in rice bran extracted, the extraction yields of fresh rice bran,expanded rice bran and defatted rice bran were60.12%,56.57%,48.23%,respectively.2. The pepides from the protein of fresh rice bran, expanded rice bran anddefatted rice bran were respectively prepared by hydrolyzing for rice bran proteinwith Trypsin，Pepsin, Neutrase, Alcalase, Papain, and the best protease and rice branprotein were chosen according to the character of hydrolysis and the antioxidativeeffect of hydrolysates against ABTS radical. The optimum conditions to achieve the maximum antioxidative ability from defatted rice bran protein with Alcalase weredetermined by response surface methodology. The results showed that Alcalase anddefatted rice bran protein were the best. The optimum hydrolytic condition forpreparation of rice antioxidant peptide were4.6,50℃,[E]/[S]1.8%,[S]5%, pH9. Therice bran antioxidant peptide produced under this condition exhibited strongscavenging activity to ABTS radical, which was up to71.85%.3. Defatted rice bran protein was used as the object. The antioxidant properties ofdefatted rice bran protein hydrolystates（DRBPHs） at various DH and differentconcen-tration were evaluated through using three kinds of antioxidant assays in vitro.The results showed that the antioxidant activities of DRBPHs were related with itsDH, and they have their own best DH in different assays, respectively. In addition, theantioxidant activities increased with the concentrations increased. DPPHradical-scavenging activities showed better effect, the EC50value was found to be0.52mg/mL, merely.4. Fraction G₄with higher antioxidant activities was separated by FibroDEAE-52and Sephadex G-15, respectively. The effect of purification was initiallyidentified by thin-layer chromatography. The amino composition of the purified G₄determined by the analysis of amino acids were Asp, Glu, Leu, Phe, Arg and Pro. Themolecular weight distribution profile of G₄determined by HPLC exhibited that themolecular weight was90.83%for low than1000, and14.38%for lower500,respectivily.