Relation between pH-induced stickiness and gelation behaviour of sodium caseinate aggregates as determined by light scattering and rheology

The effect of pH and temperature on the interaction potential of sodium caseinate solutions in terms of an adhesive-(or sticky)-hard-sphere model was studied. The sodium caseinate aggregates are regarded to be sticky hard spheres with a certain radius. The value of the stickiness parameter as deduced from light scattering is consistent with that as deduced from viscosity measurements. The stickiness between the caseinate aggregates strongly increased between a pH of 5.5 and 5, corresponding to a transition of the second viral coefficient from positive to negative, and also to the onset of gelation. The critical concentration necessary for gelation was determined to approach zero, allowing to describe the gelation using a fractal model. The fractal dimension, determined at a temperature of 293 K, increased with acidification temperature from 2.35 to 2.55 at 293 and 323 K, respectively, indicating that the pH as well as the temperature relates to the stickiness of the aggregates and can influence the final structure of the gel.