Formation of fibrillar whey protein aggregates: Influence of heat and shear treatment, and resulting rheology

We have studied the effect of a combined heat and shear treatment on the formation and rheological properties of fibrillar whey protein aggregates. The amount and length distribution of whey protein fibrils were characterized using flow-induced birefringence and transmission electron microscopy (TEM). Fibril solutions were characterized macroscopically using crossed polarizers and the flow behaviour was measured with steady-shear viscosity measurements. Fibril growth was dependent on protein concentration. The use of shear flow influenced the amount of fibrils formed when the protein concentration was sufficiently high (above 3 wt%). A shear rate was found for which the amount of fibrils was maximal. The increase in the amount of fibrils as a function of shear rate was explained by enhanced supply of protein monomers towards the fibril tips in the flow field, while the following decrease at higher shear rates could be caused by the breakage of non-matured bonds inside the fibril. Viscosity measurements of the fibril solutions showed that above a critical fibril concentration, the viscosity became independent of the fibril concentration.