This article is focused on evaluating the rheological properties of tomato ketchup. The purpose of the paper was to show the importance of knowledge about the rheological properties of ketchup and to find new more adequate equations of the temperature-viscosity dependence. All measurements were performed under the same temperature conditions at approximately 25 °C and shear velocities between 5.46 and 700.41 s-1. Ketchup is a non-Newtonian material, so the apparent viscosity was measured.
We found out that the apparent viscosity decreased exponentially with increasing temperature, so the Arrhenius equation is valid. Ketchup fluidity increases exponentially with temperature, which leads us to propose an original logarithmic expression correlating the shear stress and the square root of shear rate with only two adjustable parameters with some physical significance. The model is compared with some previous ones showing that the calculated rheological characteristics can be used to design the technological equipment or containers for the distribution of the product to the end-users. A comparison between parameter values of different fluids can contribute to the knowledge of the flow behavior is also important for the development of new recipes and the direct qualitative evaluation of the products.