Turbidity and protein aggregation in whey protein beverages.

During storage of heat-treated acidic (pH <or= 4.6) whey protein beverages, formation of protein aggregates can create undesirable turbidity and sedimentation. In this study, we found that a slow protein aggregation process controlled the rate of formation of sediment and turbidity. A heat-treated model beverage containing 12.5 g/L whey protein at a pH of 4 was stored for 6 wk at 3 different storage temperatures and analyzed for turbidity, soluble protein, and protein aggregates. One sample was stored without further treatment and the other sample was filtered to remove protein aggregates formed during heating. This was done to test the hypothesis that aggregates formed during heat treatment served as nuclei for deposition of soluble protein. Turbidity increased and soluble protein decreased as protein aggregates formed during storage. Increasing the storage temperature accelerated this process. The loss of soluble protein during storage was fit to first- and second-order kinetic equations, allowing the prediction of the effect of protein concentration, storage time, and storage temperature on the formation of protein aggregates.