Study On Preparation Of Pumpkin Seed Protein Hydrolysates And Its Antioxidant Activity

The pumpkin seeds cake is a kind of good protein resources, which is the by-product of processing pumpkin seeds. It contains rich protein and its amino acid proportion is similar with the amino acid composition of human body. As a raw material, it has great practical value and application prospect in the protein study and development. In this study, the protein of pumpkin seeds cake was extracted. The preparation of pumpkin seeds protein hydrolysates and its antioxidant activity was studied.Pumpkin seeds protein was extracted by the method of alkali extraction and alkali extraction-ultrasonic assisted respectively. According to the protein extraction rate, the best extraction conditions were determined. The results indicated:the conditions of the alkali extraction were solid-liquid ratio of1:25, alkali extaction pH of12, acid sinking pH of4.50, temperature of60℃, and the protein extraction yield was51.04%; the conditions of the alkali extraction-ultrasonic assisted were solid-liquid ratio of1:25, alkali extaction pH of12, acid sinking pH of4.5, utrasonic power of400W, time of20min, and the protein extraction yield was67.75%.According to the degree of hydrolysis, the yield of peptides and the scavenging activity of DPPH radical, the proteases were screened; the best hydrolyzing conditions were determined to selected enzymes. The results indicate:Alcalase and Flavourzyme were selected out; the conditions of the Alcalase were:temperature of55℃,[E]/[S] of6000U/g, pH of8.0, substrate of4%, time of6h; the conditions of the Flavourzyme were:temperature of50℃,[E]/[S] of800U/g, pH of7.0, time of1.5h. Under the experiment of multiple steped hydrolytic, the DPPH radical clearance rate of the enzymatic hydrolysates could achieve to76.65%.The enzymatic hydrolysates were separated into different molecular weight by the method of ultrafiltration. The invitro antioxidant activity of the enzymatic hydrolysates was studied. The results indicate:the molecular weight of hydrolysates which below3kDa maintained the optimum activity, The DPPH radical clearance rate was84.29%, hydroxy radical clearance rate was69.98%and radical clearance rate was53.80%. By animal experiment, the activity of SOD, CAT and the content of MDA in the liver of mouse were measured. The results indicate:the high, middle, low dosage groups were significantly decreased (P<0.01) than the standard group separately. So, the hydrolysates of pumpkin seed protein had the better antioxidant ability.The objective enzymatic hydrolysates were separated by Sephadex G-15and the molecular weight was measured. The target hydrolysates were separated into three constituents by Sephadex G-15, which are2738Da,521Da and181Da respectively.