Acoustic characterisation of pH dependant reversible micellar casein aggregation

Ultrasound and light-based measurements were used to monitor changes in agitated and quiescent solution characteristics such as particle size distribution during casein aggregation and redistribution in a model colloidal system. The precipitation of casein micelles was controlled by adjusting the pH of the solution to alter the stability of the micelles. The studied dispersions were prepared at high pH, taken through the isoelectric point to precipitate and then re-dispersed by further lowering the pH at specific intervals. The isoelectric point was determined by zeta potential measurement at each specific pH interval. The isoelectric point of the casein dispersions was in the region of pH 4.3–4.7. Changes in the particle size of this reversible casein system were successfully measured acoustically. The dissolution rate and solution kinetics were subsequently monitored in a wide pH range using a combination of acoustic and light-based methods.