Study On Preparation Isolated Proteins And Active Peptides From Pumpkin Seeds

In this thesis, defatted powder of pumpkin seeds was produced by supercritical carbon dioxide extraction technology. The extraction and functional properties of pumpkin seed proteins, the preparation of active peptides through enzyme hydrolysis, as well as ultrafiltration technology of enzyme hydrolysate were studied. Simultaneously, SDS-PAGE gel electrophoresis technology and gel column chromatography were respectively used to analysis the molecular weight distribution of the proteins and peptides. Then the antioxidant and ACE inhibitory activities were researched in vitro tests. Some conclusions were got as follows:1. The best conditions of alkaline extraction and acid precipitation for producing protein isolate from pumpkin seed were:a temperature of 50℃solid-liquid ratio 1:30, pH 11.0, and time 1.5h. Under these conditions, the extraction ratio was up to 85.52% and the purity of protein reached 91.07%. It was found that sulfur amino acids was the first restrictive in pumpkin seed protein, and lysine was the second one. The essential amino acid index of pumpkin seed protein is 0.8687, so it is one of good protein resources.2. The solubility of pumpkin seed protein was changed with pH. There was minimum solubility beteen the pH of 5.0 and 6.0; the water and oil absorption were both at 1.2～160 g/g or so; emulsifying ability under suitable pH reached 80%; foaming ability were relatively weak. At least 7 spectral bands were showed in SDS-PAGE electrophoresis get of pumpkin seed protein, the molecular weight mainly distributed in the 45KDa,35KDa and 25KDa below.3. The antioxidant peptides of pumpkin seed were produced by acid protease. Optimization of the process was through Plackett-Burman experimental design with the response surface methodology. Finally the best technological conditions were determined as:temperature50℃, pH 2.5, hydrolysis time 5h, substrate concentration 0.05g/ml and enzyme quantity 6000 U/g. In this condition, the scavenging activity of DPPH radical was up to 92.82%.4. The optimum parameters of antihypertensive peptides using Alcalase protease is determined primarily by single factor experiments was that: enzyme quantity 6000U/ml, pH 8, temperature 55℃, substrate concentration 0.06 g/mL, hydrolysis time 4h, then hydrolysis degree for 12.74%.5. The enzyme hydrolysate of pumpkin seed protein was ultrafiltered first as:pressure 0.25 MPa, concentration 3%, pH 7, operating time 60min; parameters of the second ultrafiltration technology as:pressure 0.2 MPa, concentration 2%, pH 7, operating time 60min. After ultrafiltration, the two kinds of hydrolysate by acid protease and Alcalase protease obtained more than 95 percent components of less than 4000Da, which had stronger antioxidant activity and antihypertensive activity respectively.