Research On Preparation Of Bioactive Peptides Prepared From Stomolophus Meleagris Protein By Enzyme Hydrolysis

Jellyfish(Rhopilema esculentum) was hydrolysed by five proteases including neutral protease, alcalase, trypsin, pepsin and papain, respectively, and we studied ACE inhibitory activity and antioxidant activity of theenzymatic hydrolysates. It showed that with degree of hydrolysis, peptide yield, DPPH radical scavenging activity and ACE inhibitory rate as index, ACE inhibition rates of jellyfish peptides hydrolysed by trypsin and alkaline protease were higher than other proteases, which reached 68.65 % and 68.89 %, respectively; DPPH radical scavenging activity of jellyfish peptide hydrolysed by pepsin, neutral protease and trypsin hydrolysis were the stronger, 90.89 %, 83.56 % and 83.85 %, respectively. Finally trypsin and alkaline were selected as tool enzymes in this study to hydrolyse jellyfish.Orthogonal experimental analysis with a 3-factor-3-level orthogonal experimental design was conducted to ascertain the optimum condition for Jellyfish hydrolysis with trypsin and alcalase. The treatment conditions of temperature, pH, enzyme/substrate ratio, substrate concentration and time on hydrolysis degree(DH) were determined. The results showed the optimum condition of trypsin for the highest values of DH when a temperature at 55 oC, a pH at 8.5, an enzyme/substrate ratio at 2.5 kU/g substrate, a substrate concentration at 4%, hydrolysis time at 2 h and the predicted values of DH was 7.34 %. The optimum condition of alkaline protease for the highest values of DH when a temperature at 60 oC, a pH at 8, an enzyme/substrate ratio at 3.0 kU/g substrate, a substrate concentration at 4 %, a hydrolysis time at 3 h and the predicted values of DH was 20.69 %. The antioxidant activity and ACE inhibition rate of jellyfish peptides prepared from above mentioned optimum condition were evaluated using different in vitro model systems. Jellyfish peptides hydrolysed by alkaline protease exhibited hydroxyl radical scavenging activity(IC50=16.57 mg/mL), DPPH radical scavenging activity(IC50=40.88 mg/m L) and its ACE inhibition rate was 75.28 % when the concentration of jellyfish peptides was 15 mg/mL.In addition, the jellyfish hydrolysates prepared by alkaline protease were modified by Plastein reaction. Some conditions of Plastein reaction were optimized with single factor experiment, and the decrease of free amino groups in reaction mixture was used as response. The optimal conditions for Plastein reaction were as follows: a concentration of jellyfish hydrolysates at 35 %, a reaction temperature at 20 oC and an enzyme/substrate ratio at 2.5 kU/g substrate. ACE inhibition rate of jellyfish peptides prepared from above mentioned optimum condition was 83.15 %(concentration of jellyfish peptides at 15 mg/m L) after 6 hours, which was increased by 10.45 %. Jellyfish peptides modified by alkaline protease exhibited hydroxyl radical scavenging activity(IC50=16.25 mg/mL); DPPH radical scavenging activity(IC50=24.68 mg/mL) which was increased by 39.63 %.At the end of the paper, proline and arginine were added to modify our hydrolysate. The conditions for Plastein reaction were as follows: the concentration of jellyfish hydrolysates at 35 %, reaction temperature at 20 oC, an enzyme/substrate ratio at 2.5 kU/g substrate and amino acid content 0.4mol/moL. Under the conditions of modification, the results showed that the ACE inhibitory activity was almost no change. The hydroxyl radical scavenging activity and DPPH radical scavenging activity of the modified peptides which was added proline were increased by 21.85 % and 31.80 %, respectively. The hydroxyl radical scavenging activity and DPPH radical scavenging activity of the modified peptides which was added arginine were increased by 7.91 % and 35.96 %, respectively. Thus, plastein reaction can improve the antioxidant activity of jellyfish peptides.