Preparation Of Angiotensin Ⅰ Converting Enzyme Inhibitory Peptides And Antioxidant Peptides From Shrimp Shell Protein

With the rapid development of aquaculture industry and marine fishing industry, up to 2010 year, the shrimp production has exceeded 3.5 million tons. If these by-production are not dealt with by time, it will cause environment pollution and resource waste. It provides a new way to increase the value of shrimp shell and a theoretical basis as food additives and functional foods by studying shrimp shell protein's functional properties and preparing ACE inhibitory peptides and antioxidant peptides with protein enzyme. The results as following:Constituent compositions of shrimp shell:water 10.95%, lipid 11.59%, crude protein 41.37%, ash 21.26%, chitin17.91%. By amino acid analysis, hydrophobic amino acid content is 25.89% out of total amino acids, which is good for preparing functional peptides. Some important functional properties of shrimp shell protein are studied, such as water solubility, water absorption capacity, oil absorption capacity, foaming properties, emulsifying activity index and bulk density. The ratio of albumin, globulin, gliadin and glutenin derived from shrimp shell is 15:2:1:7. The molecular weight of the main protein from shrimp shell is 13804Da.Many ACE inhibitory peptides which had been published in the literature collection were collected as sample, the structure-activity relationship is studied. ACE inhibitory peptides with high activity when the peptides have less residues. The activity is very significantly with the number of residues and average hydrophobicity and significant with C-terminal hydrophobicity. through principal component analysis, principal componentⅠandⅡcan describe 91.65% of the selected indicators and there is clear correlation with ACE inhibitory activity, which is positive correlation and its correlation coefficient is 0.3462.Taking hydrolysis degree and ACE (angiotensin I converting enzyme) inhibitory activity as index, shrimp shell was hydrolyzed by neutral protease,alkaline protease,bromelin and papain. Among them,the neutral protease and alkaline protease exhibited higher ACE-I inhibitory activity. So the conditions for preparation of ACE inhibitory peptides by hydrolyzing shrimp shell powder with neutral protease and alkaline protease were optimized. The results showed that the optimum conditions of enzymolysis with neutral protease were temperature 50℃, pH value 7.0, substrate concentration 2.5g/100mL, enzyme concentration 2000u/g, time 2h. Under the conditions, the inhibitory on ACE was 84.04%, the degree of hydrolysis was26.76%. The optimum conditions of enzymolysis with alkaline protease were temperature 60℃, pH value 9.5, substrate concentration 2.5g/100mL, enzyme concentration 4000u/g, time 2.5h. Under the conditions, the inhibitory on ACE was 67.70%, the degree of hydrolysis was 69.79%. through ultrafiltration, the production is seperated into 3 parts by molecular weight. The peptides whose molecular weight are less than 5000 show the highest activity. The peptides whose molecular weight less than 5KDa are seperated by Seprodex G-25. From the pepetides enzymed by neutral protease there are 5 peaks whose molecular weights are 794.88Da,569.77Da,456.35Da and 262Da seperately, and by alkaline protease 3 peaks are detected whose molecular weights are 711.38Da,365.51Da and 262Da. So these peptides with strong ACE inhibitory activities are reasoned to contain 2 to 6 amino acid.Use DPPH radical scavenging activity and FRAP reducing power as index, shrimp shell is hydrolyzed by neutral protease, alkaline protease and papain. Among them, the production hydrolyzed by papain exhibited higher DPPH radical scavenging activity and the production hydrolyzed by alkaline protease exhibites higher FRAP reducing power, so papain and alkaline protease are chosen to be optimized. The results show the optimum conditions of enzymolysis with papain are temperature 65℃, pH value 6.5, substrate concentration 2.5g/100mL, enzyme concentration 2000u/g, time 2.5h. under the condition, DPPH radical scavenging activity is 94%. The optimum conditions of enzymolysis with alkaline protease are temperature 50℃, pH value 10, substrate concentration 6.5g/100mL, enzyme concentration 3500u/g, time 2.5h. under the condition, the FRAP reducing power is 1.501nmol/ml.