Effect of pH and ionic strength on apple juice turbidity: Application of the extended DLVO theory

This work studied the effect of liquid medium pH and ionic strength on the stability of apple juice particles. Colloidal interactions between them were modeled with the extended DLVO theory. Considering that repulsive forces provide sol stability, its turbidity was modeled to be the sum of a “hydration contribution” plus an “electrostatic contribution”. Sol turbidity followed a linear relationship with the energy barrier between pairs of particles, which prevents their agglomeration (energy barrier information was obtained from viscosity—particle volume fraction data). The turbidity predicted for zero energy barrier was significantly high, indicating that particles were inherently stable. This was attributed to an immobilized water layer coating them (the primary hydration shell). Energy barrier was governed by changes in particles surface charge (ζ potential) and hydration constant: they decreased at decreasing pH and increasing ionic strength. ζ potential's reduction was attributed to neutralization of particles negative charge, and compression of the electrical double layer surrounding them, respectively. Hydration's decrease was attributed to the distortion of the outer hydration shells by hydrated cations attracted by particles negative charge.