Study On Extraction,Isolatin And Purification Of Proteins From Rapeseed Meal Defatted With High Temperature And Modification On Functional Properties Of Protein By Hydrolysis

The methods of Alkali-dissolution and Cellulase-hydrolysis were respectively used in the extraction of proteins from rapeseed meal, and the parameters of these processes were optimized. Acid-deposition and ultra-filtration were used during the isolation of proteins to get the rapeseed protein isolate, and the technics of two processes were studied. Then, the rapeseed protein isolates were purified with anion-exchange chromatography and analyzed by SDS-PAGE after purification. In the meantime, changes on functional properties of rapeseed proteion isolate were analyzed during the process enzyme hydrolysis.Cellulose hydrolysis was used to pretreat the rapeseed meal before extraction of proteins under the condition of pH9.0. The parameters of Cellulose hydrolysis were optimized with orthogonal test. The optimum parameters were:temperature55℃, pH5.0, time2.5h, addition of enzyme0.3%. The results showed that the extraction ratio of protein was42.34%with the treatment of cellulose hydrolysis, while28.07%without the treatment of cellulose hydrolysis. The extraction ratio of protein was improved by50.83%.Alkali-dissolution was used in the extraction of proteins. According to the experiments of single factors and Plackett-Burman design, it was found that pH、temperature and times of extraction the key factors to the extraction were pH, temperature and times of extraction. The levels of the three factors were optimized by response surface method. The optimum parameters were obtained, as follows:pH13, temperature49.19℃, times of extraction3. Under the conditions, the protein extraction yield was89.92%.The optimum parameters of acid-deposition were:pH of acid-deposition4.5. Under the conditions, the maximum predictive value of protein deposition yield was53.46%. Orthogonal test was applied to study the parameters of ultra-filtration, and the optimum parameters were obtained, as follows:pressure0.15MPa, pH9.0, temperature40℃. The isolated proteins were obtained through spray drying, the purity of which was76.58%, and the final recovery rate of protein was68.76%. The rapeseed protein isolate was analyzed by electrophoresis after purification with anion-exchange chromatography. The result of electrophoresis indicated that rapeseed protein isolate was mainly composed of five components, the molecular weights of which were respectively28KKD、24KD、22KD、19KD、17KD.The rapeseed protein isolate was hydrolyzed by acidic protease and the degree of hydrolysis was about10%under the hydrolysis condition as follows:addition of enzyme20U/g, temperature40℃, pH3.0, time of hydrolysis2.5h. It was studied that changes on solubility, water-absorbing capacity, foaming capacity, foaming stability, emulsifying activity and emulsifying stability during the process of hydrolysis, in the meantime soybean protein was compared with rapeseed protein. It was indicated that, compared with non-hydrolyzed rapeseed protein isolate, the hydrolyzed rapeseed protein isolate was better in solubility, foaming capacity. The solubility was improved by67.84%, the foaming capacity was improved by57.14%, and there was no difference between the hydrolyzed and non-hydrolyzed rapeseed protein isolate in emulsifying activity and emulsifying stability. In the meantime, the solubility of hydrolyzed rapeseed protein isolate was14.29%higher than soybean protein, the foaming capacity of hydrolyzed rapeseed protein isolate was29.41%higher than soybean protein, and there was no significantly difference in emulsifying activity.