| Clam is an important marine shellfish resource in China, which is not only of abundant nutrition, delicious, but also has many health functions, so it is of important dietary value and economic value. There are extremely rich resources from north to south, throughout the coastal areas, about hundreds of thousands of tons clams a year come out, so they have great development potential. Clams, which are rich in protein and contain the full range of amino acids, are good raw materials for the development of bioactive peptides by hydrolysis. In this paper, as raw material, clam meat was processed through the technology of enzyme and ultrafiltration to obtain ACE inhibitory peptides, at the foundation of structure-activity relationship of ACE inhibitory peptides.First of all, many ACE inhibitory peptides which had been published in the literature collection were collected as samples, the structure-activity relationship of which was studied. The results showed that aquatic and animal protein were ideal sources for ACE inhibitory peptides; ACE inhibitory activity would be higher, when the N-terminal was Val , Ile, Leu, Gly, Phe, Lys, Met or the C-terminal was Pro, Tyr, Lys ,Try. Through principal component analysis, we found that an overall evaluation of most ACE inhibitory peptides was around zero.Secondly, based on the structure-activity relationships and specificities of enzyme, the hydrolyzation of clam meat by several proteolytic enzymes were discussed with gel chromatography. The results showed that in the products hydrolyzed by Alcalase,peptides with wide molecular weight distribution were obtained. In the products hydrolyzed by acid protease,peptides with small molecular weights were predominated. In the products hydrolyzed by neutral protease,peptides with molecular weights about 1000 and above 5000 were predominated. In the products hydrolyzed by trypsin and flavourzyme,peptides with molecular weights above 1500 was predominated. Enzymes were sorted by the ACE inhibition rate of their hydrolysates: trypsin> flavourzyme > neutral protease> acid protease> Alcalase. The specificities of enzyme showed optimum choices for preparing ACE inhibitory peptides were neutral protease and the combination of Alcalase and trypsin.Then, the conditions of neutral protease and the combination of Alcalase and trypsin were optimized. The results showed that at the natural pH7.2~7.5 and the substrate concentration 2.5:100, the optimal hydrolyzation conditions of the neutral protease is temperature 55℃, the enzyme 3%(30000u/g·pr), 4 h. at this condition, the protein dissolution rate was 68.4%, ACE inhibition rate was 32.31% when the protein concentration was1mg/mL, the optimal hydrolyzation conditions of Alcalase was as follows: the enzyme 2%(20000u/g·pr), pH9.0, 60℃, substrate concentration 2.5:100. the degree of hydrolysis was up to 17.86% after 2h. the effect of Alcalase hydrolysis time (t1) and trypsin hydrolysis time (t2) on the ACE inhibitory activity was investigated. It was showed that when t1 was 34.3min and t2 was 12.9min, protein dissolution rate was 79.0% and ACE inhibition rate was up to 36.00% (when the protein concentration was1mg/mL) which were higher than the neutral protease hydrolysate.Finally, the effect of ultrafiltration on ACE inhibitory activity was discussed. Ultrafiltration could concentrate the ACE inhibitory peptides, and improve the ACE inhibition rat. A kind of ACE inhibitory peptides which molecular weight were less than 3000 , with ACE inhibition rate 64.91%( when the protein concentration was1mg/mL) was prepared by the combination of Alcalase and trypsin. The ACE inhibition rate slightly decreased after in vitro digestion.
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