Abstract: In this study, egg white protein prepared from commercial fresh eggs was subjected to pasteurization or ultra-high pressure (UHP) sterilization (200–300 MPa and 2.5–12.5 min). After spray drying, circular dichroism (CD) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, ultraviolet (UV) spectroscopy, fluorescence spectroscopy and a dynamic light scattering laser particle size analyzer were employed to characterize the effects of the sterilization treatments on the conformation, particle size, surface potential, and foaming characteristics of egg white protein. The results showed that both pasteurization and ultra-high pressure sterilization irreversibly changed the conformation of egg white protein. The relative contents of α-helix and random coil increased, whereas the relative contents of β-sheet and β-turn decreased with increasing sterilization pressure. After UHP treatment, the fluorescence intensity decreased, and it increased first and then decreased with increasing pressure and dwell time. UHP treatment resulted in the exposure of tyrosine, tryptophan and phenylalanine residues, but the exposed amino acid residues were re-buried inside the protein molecule with increasing dwell time. In addition, high pressure induced the aggregation of egg white protein. The particle size increased first and then decreased with increasing sterilization pressure and holding time, and the particle size distribution became more uniform. At 300 MPa, the surface potential, foaming ability and foam stability increased with increasing sterilization time up to 7.5 min and then decreased. At 200 and 250 MPa, the foam ability and foam stability continuously increased. Compared with pasteurization, ultra-high pressure sterilization caused greater damage to the secondary structure and less damage to the tertiary structure, and effectively improved the polydispersity index, surface potential, foamability and foam stability of egg white protein.

Key words: egg white protein; secondary structure; tertiary structure; ultra-high pressure sterilization