In order to find an effective method to reduce the immunogenicity of egg white protein, the immunogenicity of egg white protein was determined by enzyme-linked immunosorbent assay (ELISA) and its structural characterization was carried out by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), Fourier transform infrared (FTIR) spectroscopy, fluorescence spectroscopy and ultraviolet (UV) spectroscopy after being treated by microwave, enzymatic hydrolysis or microwave-assisted enzymatic hydrolysis. The results showed that microwave treatment at 700 W for 20 s and alkaline protease hydrolysis decreased the immunogenicity of egg white protein by 50.81% and 55.83%, respectively. A more pronounced effect was observed with microwave-assisted enzymatic hydrolysis, decreasing the immunogenicity of egg white protein by up to 67.48%. The SDS-PAGE band pattern changed after each treatment. Fluorescence spectroscopic results demonstrated that the three treatments could alter the microenvironment of amino acid residues. FTIR spectra indicated the transformation of the secondary structure of egg white protein to a disordered conformation and changes in both secondary and tertiary structures. In addition, the surface hydrophobicity increased after the treatments. These results suggested that the reduction in the immunogenicity of egg white protein may be related to its structural change. Microwave-assisted enzymatic hydrolysis is more effective than either alone in reducing the immunogenicity of egg white protein.

In order to develop special liquid egg yolk for making of egg tart, the effects of ultrasound-assisted chitosan treatment on the emulsification properties of liquid egg yolk and structure of egg yolk proteins were investigated in this study. The emulsification properties of fresh egg yolk, egg yolk added with chitosan, heated egg yolk, heated egg yolk added with chitosan, ultrasound-treated egg yolk and ultrasound-assisted egg yolk added with chitosan were evaluated by measuring emulsifying activity, emulsion stability and particle size, as well as microscopic observation. Egg yolk protein structure was characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), Fourier transform infrared (FTIR) spectroscopy, and fluorescence spectroscopy. The results showed that compared with the untreated samples, ultrasound-assisted chitosan treatment increased the emulsifying activity of liquid egg yolk by 29.51% and the emulsion stability by 9.47%, decreased the particle size by 50.01% and the interfacial tension by 16.67%, and smoothened the interfacial tension curve. The combined treatment reduced the size of emulsion droplets and increased the dispersivity of egg yolk particles as observed by scanning electron microscopy (SEM). The intensity of protein bands in SDS-PAGE was decreased after the combined treatment, which resulted in protein unfolding and exposure of hydrophobic amino acid residues and increased the surface hydrophobicity of liquid egg yolk increased by 12.91%. Moreover, the relative contents of α-structures and β-structures in proteins were reduced after the treatment and the relative content of random coil was increased by 5.26%, indicating that ultrasonic-assisted chitosan treatment led to more disordered and loose protein structure, and the increase of hydrophobicity could promote the emulsifying properties. In summary, this study demonstrates the great potential of ultrasound-assisted chitosan treatment to enhance the emulsification properties of liquid egg yolk for baking purpose.

In order to increase the pasteurization temperature and heat resistance of liquid egg white, the effect of trypsin modification on the heat resistance and structural properties of liquid egg white was investigated in this study. The sample in this study consisted of two groups: unmodified and enzyme-modified. Each group was kept at 25 ℃ (control) or sterilized at 56, 62, 68 or 72 ℃ for 3 min. The changes of heat resistance were measured by turbidity and supernatant protein content, and the structure of egg white protein was characterized by apparent viscosity, particle size, surface hydrophobicity, Fourier transform infrared (FTIR) spectroscopy, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and scanning electron microscopy (SEM). Trypsin modification significantly reduced egg white turbidity and increased the protein content of the supernatant (P < 0.05). As the sterilization temperature increased, the turbidity and particle size of egg white gradually increased, while the protein content of the supernatant gradually decreased. At the same sterilization temperature, the turbidity and apparent viscosity of the modified egg white were significantly lower, while the surface hydrophobicity was significantly higher (P < 0.05) and the particle size distribution was closer to the normal distribution compared with that of the unmodified egg white. Enzymatic modification could inhibit protein thermal aggregation and improve heat resistance. SEM results showed that enzymatic modification increased the surface porosity of egg white protein and the dispersity of the particles; at the same sterilization temperature the number of particles retained on the surface was higher in modified than in unmodified egg white. SDS-PAGE analysis showed that enzymatic modification promoted the degradation of large molecular mass proteins in egg white. Fourier transform infrared spectroscopy showed that at temperatures below 68 ℃, the relative content of α-helix of the modified egg white was significantly higher than that of the unmodified egg white (P < 0.05), while the relative content of random coil was significantly lower than that of the unmodified egg white. In conclusion, trypsin can effectively improve the thermal aggregation of egg white proteins during heat sterilization and improve the heat resistance of liquid egg white, which is important for expanding its sales radius.

This study established a rapid and efficient technique to detect the freshness and yolk-to-white ratio of liquid egg based on conductivity combined with salinity, total dissolved solids (TDS), pH, and color parameters. The results showed that during the storage period of 0-45 days at 4 ℃, the conductivity, salinity, and TDS of egg yolk and egg white gradually increased. The color difference index and egg yolk pH of both decreased significantly, while the pH of egg white gradually increased. It was found that the accuracy of conductivity in detecting the freshness of egg yolk and egg white was 91% and 89%, respectively, while that of conductivity combined with other indices was 94%. Based on this, the criteria to classify liquid egg into four grades of AA, A, B and C were established for the first time. AA liquid eggs were selected to detect yolk-to-white ratio using conductivity as the major index combined with salinity, TDS and pH. The experimental results proved that the conductivity, salinity, TDS and pH were all highly significantly and linearly correlated with the proportion of egg yolk in liquid egg; therefore, the proportion of egg yolk in unknown liquid egg samples could be detected based on the regression equations. The ExpAssoc model showed an average relative error of 8.87%, indicating high reliability. The results of this study provide a theoretical basis for the detection of the freshness and yolk-to-white ratio of blended liquid egg, and provide a reference for industrial producers of liquid egg.

In order to explore the predictive bactericidal effect of ultrasound-assisted steam treatment on Escherichia coli on the eggshell surface and the mechanism of bacterial damage and death, a kinetic model for the sterilization of E. coli on the eggshell surface by ultrasound-assisted steam treatment was constructed. By controlling the concentration of bacterial suspension used to artificially contaminate eggshells, the sterilization efficiencies of E. coli by ultrasound, steam and their combination were evaluated and compared with that using the sodium hypochlorite immersion method, commonly used in commercial sterilization. The Linear, Weibull, Log-Logistic and Modified Gompertz models were used to fit the inactivation curve of E. coli by ultrasound-assisted steam treatment, and the damage degree of cell morphology and the leakage of cell contents before and after sterilization were measured. The results showed that after 180 s of 150 W ultrasonic pretreatment and 3 s of steam treatment, the logarithm of the total number of E. coli decreased from 6.26 to 2.04 with a mortality rate of 67%. The sterilization process of ultrasound-assisted steam treatment was better fitted to the nonlinear dynamic model, while the Weibull model was more suitable to describe the dynamic process of sterilization with increasing ultrasonic intensity and steam treatment time. In addition, the combined treatment destroyed the ultrastructure of E. coli and the external structure of its cells, resulting in cytoplasm leakage and changes in the permeability of the membrane. Therefore, ultrasound-assisted steam treatment could aggravate the deformation and damage of bacteria, leading to bacterial death. The experimental results provide a theoretical basis for the inactivation of E. coli on the eggshell surface. According to the results of egg quality during storage, this method has broad application prospects in the production of clean eggs.