This work investigated the impact of lactose crystallization in milk protein concentrate and its effects on rheology. Crystallization was conducted with varying levels of total solids (44, 46, and 48%), temperature (15, 20, and 25 degrees C), and alpha-lactose monohydrate powder size (40 and 100 mesh) as seed crystals. Concentration of total solids was the most important factor affecting crystallization rate. MPC 42 concentrates exhibited a non-Newtonian shear thinning behavior. The difference in viscosities among the total solids content was caused by the amount of crystal mass and not by the total solids itself. Samples seeded with 100 mesh lactose seed exhibited a significantly higher consistency index, higher yield stress, and lower flow behavior index than samples seeded with 40 mesh seeds. A second order polynomial model provided empirical relationships between rheology and volume fraction. (C) 2017 Elsevier Ltd. All rights reserved.