In this work the influence of temperature and solid matter content on the viscosity of model systems prepared with tribomechanically treated as well as untreated whey proteins and skim milk powder was investigated. The rheological properties of model systems were determined using a rotational rheometer Rheometric Scientific RM-180, and described by the Ostwald de Waele "power law". Significantly higher viscosity was found for model systems prepared with tribomechanically treated materials compared to those prepared with untreated materials. Systems with higher protein content (WPC-80) exhibited greater viscosity than those with lower protein content (WPC-60). The lowest viscosity was found for systems prepared with skim milk powder. The correlation between viscosity and temperature (0-60 degreesC) was determined by an Arrhenius model. Because of a very high regression coefficient (0.91-0.98) achieved for the investigated systems, the Arrhenius model can completely describe the viscosity change in the given temperature range. Activation energy of viscous flow was significantly higher for all tribomechanically treated systems, because tribomechanical micronisation decreases particles size and enables their better hydration. (C) 2004 Elsevier Ltd. All rights reserved.