The Preparation Of Active Peptide From Salted Egg White By Emzymic Hydrolysis And Its Antioxidant And Antimicrobial Activity Studied

In this paper, the technology of extracting ovalbumin peptides was optimized.at first, and then papain and acid protease were used as the hydrolytic enzymes. The enzymatic reaction conditions including enzyme species, substrate concentration, enzyme concentration, pH value, temperature and reaction time was studied successively by single factor experiment. The optimum enzymolysis condition of salted egg white was obtained with papain substrate concentration 3%, dosage of enzyme 5000 U/g, hydrolysis temperature 50℃, pH 5.5, and reaction time 6 h. The optimal parameters of acid protease hydrolysis were as follows:substrate concentration 2%, dosage of enzyme 5000 U/g, hydrolysis temperature 55℃, pH 3.0, and with reaction time of 6 h. The best way of the enzymolysis by complex of papain and acid protease was as follows:the first reaction lasted 4h with papain, then acid protease enzyme was also added and kept reaction 2 h, and the ratio of two added enzymes was PP:AP=3:2.According to the hydrolysis’s features, a series of desalination methods cuch as chromatography and membranes filtration methods were used for desalination of salted egg white hydrolysates. Desalination rate, protein recovery and salt content of final products were used as indicators. G-25 chromatography can get a good desalinization result with desalting rate of 91.64%, protein retention of 86.25%, and final salt content of 4.25%, but the cost was high and preparation quantity was small. The desalinization rate and protein retention of DA201-C were 93.74% and 75.25%, respectively, which indicated a good desalinization effect. Using the nanofiltration for desalinization, the desalinization rate, protein retention and the salt content of the final product were obtained as 92.31%,90.38% and 2.25%, respectively. This method can be widely applicated in industrial production. Combing nanofiltration with G-25 chromatography, the final products with salt content 0.17% can be obtained.The range of molecular weight, amino acid compotents, physical and chemical properties of hydrolysates were determinated. G-25 chromatography mentod and HPLC were used to determine the molecular weight of peptides. The G-25 chromatograhy results showed that the molecular weights of acid protease enzyme products were in the range of 3554 Da-1364 Da, the molecular weights of papain products were lower than 2151Da, and the molecular weights range of complex enzymes products were 1785 Da-318 Da. The HPLC result revealed that the major substances of salted egg white hydrolysate were small peptides which molecular weight was in the range of 70-14057Da. The essential amino acids of salted egg white peptide to total amino acids were 42.16%, indicating the good nutrition value of salted egg white peptide. The SRC was 66.6173% with reference to FAO/WHO mode, and 51.7966% with reference to chicken egg mode. The salted egg white peptide had a good solubility, foamability, thermal stability and storage stability.In this paper, the antioxidant and anti-bacterial functions of salted egg white peptide were studied. The results showed that the salted egg white peptide had scavenging capacity of hydroxyl radical and superoxide anion. The peptide with 20mg/ml had hydroxyl radical scavenging rate of 70.54%, and superoxide anion clearance rate of 64.71%. The components with molecular weight of 2000 Da-1000 Da had the strongest antioxidant capacity, while components with molecular weight less than 200 Da had the weakest antioxidant capacity. The free radical scavenging ability of three kinds hydrolysates were weaken in the order of the complex enzyme> the papain> the acid protease hydrolysates. The anti-oxidation function of salted egg white peptide had a good thermal stability, but it was sensitive to the pH value. The salt can reduce the free radical scavenging capacity of salted egg white peptide.The salted egg white peptide can inhibit the E.coli, Salmonella and Staphylococcus aureus with MIC were 0.6%,0.4% and 0.6%, respectively. Micro-structure of bacteria was observed with collapse and depression after peptide being acted on the bacteria. The components with molecular weight of 2000 Da-1000 Da had strongest inhibition effect on E.coli and Salmonella. The components with molecular weight of 1000 Da-400 Da had strongest inhibition effect on staphylococcus aureus bacteria. The components with molecular weight lower than 200 Da had the weakest inhibition effect. Salt can reduce the peptides’ antimicrobial at a certain concentration,. The antimicrobial of salted egg white peptide was higher than fresh duck egg white peptide. The antimicrobial of duck egg white hydrolysates was higher than egg white hydrolyzate. The antimicrobial of salted egg white had a good thermal stability and was sensitive to the pH value.