Investigation of how agitation during precipitation, and subsequent processing affects the particle size distribution and separation of α-lactalbumin enriched whey protein precipitates

In this work, α-lactalbumin (α-la) rich precipitate particles are formed and aged in a batch stirred-tank from a whey protein concentrate (WPC) dispersion. Precipitation of the proteins occurs during a period of acid-addition followed by an ageing period. This study investigates how stirred-tank impeller agitation and subsequent processing, by means of passing precipitate suspensions through a capillary tube or a partially open ball-valve, affect particle size and composition. Precipitate particles are largely unaffected when subjected to laminar capillary tube flow. However, as flow becomes transitional and thereafter turbulent, particle breakage increases, especially for precipitates formed and aged under mild agitation conditions. Precipitates passed through the ball-valve experience even greater particle size reduction as a sharp geometrical transition results in highly turbulent flow. Moreover, particles formed and aged under low shear conditions, though initially larger, are in fact weaker and fragment to a greater extent during turbulent processing through the ball-valve. This has process design implications for separation processes where particle size is important, as shear history can influence particle toughness. Substantial size reduction of particles can best be mitigated by identifying regions of high turbulence or sudden changes in flow geometry, and by redesigning these regions so as to reduce these effects.