Effect Of Oxidation On Structure And Functional Properties Of Egg White Protein

Egg white protein contains more free amino residues, are very sensitive to oxidation.Egg white protein will be oxidized by pro-oxidative factors in the process of production,which may lead to the oxidative aggregation of protein with structure and functional properties changed, and ultimately affect the nature of the product. In this paper, the hydroxyl radical-generating system was used, which was composed of hydrogen peroxide/ ferric chloride / ascorbic acid (H2O2 / FeCl3/ Asc),Egg White Protein was oxidatively stressed by incubation at room temperature for 3 h in hydroxyl radical-generating media containing 0.1 mmol/L ascorbic acid, 0.1 mmol/L FeCl3, and 1 mmol/L-20 mmol/L H2O2.Oxidation degree of Egg white protein was characterized by the changes of carbonyl content, free amino acid content and dityrosine content. Particle size distribution, solubility and turbidity were used to characterize the agglomeration characteristics of the egg white proteins. Surface hydrophobicity index of the egg white proteins was studied the effect of oxidation on the hydrophobic interaction. The change of intermolecular forces of egg white protein were studied the effect of driving force of the protein modified by oxidation,free sulfhydryl, total sulfhydryl content and Fourier transform infrared spectroscopy were used to determinate the effects oxidation on aggregation and secondary structure of egg white proteins. The results found that carbonyl content and dimer tyrosine content of egg white protein increased(P<0.05) with increasing concentrations of H2O2, compared with the control group,when the concentration of H2O2 up to 20 mmol/L,their content increased by 513% and 48.87%, respectively, free amino acid content decreased, while the concentration of H2O2 is 1 mmol/L and 5 mmol/L, compared with the control group,the content was reduced by 10.2% and 15.0%, respectively, and as the oxidation degree becoming more serious, the bigger drop, The HRGS-oxidized egg white protein showed a higher dityrosine content, and turbidity (P<0.05) than unoxidized egg white protein,surface hydrophobicity decreased(P<0.05) in a similar fashion,The free sulfhydryl and disulfide bond content decreased(P<0.05),the relative content of a-helix was the highest at 5 mmol/L, and then decreased with the increase of H2O2 concentration. Random coil have no obvious variety regulation. The relative contents of Beta Angle increased first, then decreased, and beta folding is elevated in low concentration, protein oxidation can be led to the formation of egg white protein aggregation, and when the concentration of up to 10 mmol/L, 20 mmol/L, relative content reduce, egg white protein peptide chain break,further lead to protein structure has changed.The emulsions, egg white protein exposed to hydroxyl free radical and soybean oil were prepared by high speed shearing machine, and the emulsifying property and emulsifying stability were determined by turbidity method. It was found that emulsification ability and emulsion stability of egg white protein, with increasing concentration of H2O2 showed a trend of increase gradually decline. In addition, NaCl,sucrose and soluble starch were added to the oxidized egg white protein to study the effect of ionic strength and the increase of polysaccharide on the emulsifying properties.It was found that the ionic strength and the increase of the polysaccharide resulted in the change of the emulsifying ability and emulsifying stability of the oxidized egg white protein to varying degrees.The effect of physicochemical modification on the foaming property of egg white protein was studied by pH, temperature, adding sucrose and NaCl. The results showed that the oxidation of egg white protein caused the foaming ability and stability of egg white protein to some extent were improved.foam and foam stability were better at pH 2 and 4. When the temperature were between 30℃ and 60 ℃, the foaming ability and foam stability of the egg white protein gradually increase with the temperature increasing. The addition of sucrose reduced the foaming ability of the oxidized egg albumin but increased the stability of the foam. whereas the addition of NaCl increased the foam stability of the oxidized egg albumin. The addition of NaCl, sugar and soluble starch in oxidized egg white protein, changed the emulsification ability and stability, to some extent.