Preparation And Characteristics Of Antioxidant Peptides From Egg White

To explore the bioactivity of polypeptide derived from egg white protein(EWP),the EWP was hydrolyzed by protease to obtain the antioxidant peptides with controlling enzymolysis technology. The optimum hydrolysis protease and hydrolysis condition were selected by contrast experiment and orthogonal experiment with DPPH radical scavenging capacity and degree of hydrolysis as investigating index,and the hydrolysis effect of the EWP was tracked by SDS-PAGE gel electrophoresis.At the same time, the structure changes of egg white in the hydrolysis process were inspected with Scanning election microscope. Antioxidant activity of the egg white before and after enzymolysis were investigated, and the stability of the obtained antioxidant peptides were researched. The results showed that:(1)Among the hydrolysates resulting from three enzymes under the same substrate protein concentration, enzyme dosage and hydrolysis time, the highest antioxidant activity was observed in the alkaline protease hydrolysate at 7 h hydrolysis, which presented 68.37% DPPH scavenging activity, that of neutral protease hydrolysate came second, and trypsin hydrolysate was the worst. SDS-PAGE gel electrophoresis revealed that the molecular weight of the EWP mainly gathered in10~100 kDa. Alkaline protease displayed the best hydrolysis effect, and the band of protein degraded entirely after 7 h, so the Alkaline protease was the optimum hydrolytic enzymes to prepare egg white antioxidant peptides.(2)The protein concentration(P=0.01<0.05) and enzyme dosage(P=0.042<0.05)were the main influence to the DPPH scavenging activity of the hydrolysates. The optimal hydrolysis conditions for preparing egg white antioxidant peptides were that the egg white was hydrolyzed by 18000U/g alkaline protease at 40 mg/ml protein content and pH 9.0 under 60℃for 7h. The freeze-dried powder of the EWP presented surface-smooth plate like crystals before enzymatic hydrolysis, however the surface appeared the porous honeycomb structure after enzymatic hydrolysis, and the freeze-dried powder of enzymolysized sediment became loose, presenting flocculentstructure and not being crystal. So there had been greet changes in the structure of egg white protein after hydrolyzed by Alkaline protease.(3)By the contrast, the power of scavenging of superoxide anion grew nonlinearly along with increasing concentration of egg white antioxidant peptides. As with increasing concentration of egg white antioxidant peptides, the Reducing power and scavenging of DPPH radical and hydroxyl radical grew linearly, but the antioxidant activity were all lower than that of Vc.(4)The egg white antioxidant peptide has a good heat-resistant ability; PH,glucose, sucrose, NaCl and Sodium benzoate have no significant influence on the antioxidantion of the egg white antioxidant peptide. Zn2+ and Cu2+can reduced the antioxidant activity of the antioxidant peptide obviously. As the increasing content of K+, the antioxidant activity reduced lightly. Both Ca2+and Mg2+ had no effect on the antioxidant activity retention.