Acid-induced acceleration of kinetics and dynamics during thermal gelation of egg yolk

Abstract

The effect of lowered pH on the thermal gelation behavior of hen egg yolk was investigated over the temperature range of 58–72 °C using low-dose X-ray photon correlation spectroscopy in ultra-small-angle X-ray scattering geometry. Progressive structural and dynamical alterations were observed at room temperature with decreasing pH, indicative of acid-induced protein denaturation, which correlates with an increase in yolk viscosity. Temperature- and pH-dependent structural and dynamic investigation suggests an acceleration in gel formation with decreasing pH. The time–temperature superposition relationship observed in all samples suggests an identical mechanism underlying protein aggregation–gelation with a temperature-dependent reaction rate. The sol–gel transition time extracted from kinetic and dynamic information follows Arrhenius behavior, with no significant change in the activation energy (450 ± 20 kJ/mol) of gelation. However, the prefactor A systematically decreases with decreasing pH, indicating that acidification accelerates gelation primarily by increasing the frequency of productive encounters without altering the fundamental energy barrier of the process.