Effect of Trypsin Modification on Heat Resistance and Structural Properties of Liquid Egg White during Heat Sterilization

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.