Extraction And Enzymatic Modification Of Rapeseed Protein From Hyperthermia Rapeseed Meal

The technical parameters of exatracting protein from industrical rapeseed meal by means of combination method and proteinase method were established respectively. The structure and functional properties of extracting rapeseed protein were studied. Finally, the functional properties of rapeseed protein that was limited hydrolysis by neutral proteinase and alkaline proteinase were inestigated, too.The optimum extracting rapeseed protein technical parameter of combination method were as follows: enzyme does 2.5%, ratio of material to solvent 1:20, pH7.0, 50℃, reaction time 3h; aqueous alkali pH10.0, 55℃, 2h, ratio of material to solvent 1:12, and the extraction rate of rapeseed protein was 71.63%. The extraction was precipitated at isoelectric points, and then decolorized by 70% ethanol. The purity of isolated rapeseed protein was 78.44%, contents of tannin, phytic and glucosinolate were 1.14%, 1.05% and 0.17mg/g, respectively. Glucosinolate content is lower than edible grade (The glucosinolate content is lower than 0.4mg/g in food).The optimum parameters of neutral proteinase method were as follows: enzyme does 1%, ratio of material to solvent 1:20, pH7.5, 55℃, extracted 3h, and the extraction rate of rapeseed protein was 76.16%. The purity of rapeseed protein was 67.84%, contents of tannin, phytic and glucosinolate were 2.04%,1.65%,1.78mg/g, respectively. The product is only suitable for feed additive.To study molecular composes and structure of both extracted rapeseed protein, the result showed: amino acid composition of both extracted rapeseed protein were simliar. Rapeseed protein which was prepared by combination method had much more large molecular weight of protein, its relative molecular mass distributed at 279000Da, 12600Da, and 4200Da, the elution area accounted for 38.96%, 17.76% and 41.63%, respectively. Rapeseed protein by proteinase method had much more small molecular weight of protein, its relative molecular mass mainly distributed at 288000Da, 62000Da and 3005Da, the elution area accounted for 5.13%,7.18%,85.62%, respectively. circular dichroism (abbreviation CD) spectrum indicated differences between extracted protein by combation method and prepared protein by proteinase method on secondary structure, there wereα-helix,β-sheet,β-turn and random coil 51.27%, 1.22%, 21.68% and 25.84% in former rapeseed protein and 35.09%, 1.13%, 24.11 and 39.70% at other protein. CD spectrum also indicated that the marked differences both of them on secondary structure. The functional properties of limited hydrolysis rapeseed protein were researched, and the results showed that solubility of limited hydrolysis rapeseed protein was improved. The solubility of DH10 rapeseed protein was 57.11% and 63.82% at pH7.0, respectively. The emulsion of DH2 hydrolysate was the best. The oil-holding capacity and water-holding capacity of neutral proteinase hydrolysate was maximum at DH2, the alkaline proteinase hydrolysate showed the best oil-holding capacity at DH8 and water-holding capacity at DH2. Relative molecular weight of rapeseed protein hydrolysate was decreased with the DH increased, so it was important to control DH for special functional property protein.