Effects of temperature and ionic strength on the microscopic structure and dynamics of egg white gels

We investigate the thermal gelation of egg white proteins at different temperatures with varying salt concentrations using x-ray photon correlation spectroscopy in the geometry of ultra-small angle x-ray scattering. Temperature-dependent structural investigation suggests a faster network formation with increasing temperature, and the gel adopts a more compact network, which is inconsistent with the conventional understanding of thermal aggregation. The resulting gel network shows a fractal dimension delta, ranging from 1.5 to 2.2. The values of delta display a non-monotonic behavior with increasing amount of salt. The corresponding dynamics in the q range of 0.002-0.1 nm(-1) is observable after major change of the gel structure. The extracted relaxation time exhibits a two-step power law growth in dynamics as a function of waiting time. In the first regime, the dynamics is associated with structural growth, whereas the second regime is associated with the aging of the gel, which is directly linked with its compactness, as quantified by the fractal dimension. The gel dynamics is characterized by a compressed exponential relaxation with a ballistic-type of motion. The addition of salt gradually makes the early stage dynamics faster. Both gelation kinetics and microscopic dynamics show that the activation energy barrier in the system systematically decreases with increasing salt concentration.

Automated summary

We investigated the thermal gelation of egg white proteins at different temperatures and salt concentrations using x-ray photon correlation spectroscopy. The temperature-dependent structural investigation showed that a higher temperature led to faster network formation and a more compact gel network, contradicting the conventional understanding of thermal aggregation. The gel network exhibited a fractal dimension ranging from 1.5 to 2.2, which displayed non-monotonic behavior with increasing salt concentration. The addition of salt accelerated the early stage dynamics and reduced the activation energy barrier in the system.