On the selected rheological properties of commercial ketchups

Abstract

The rheological properties of four different ketchups were determined. The viscosity, shear rate and shear stress were measured by use of Anton Paar DV-3 P Digital Viscometer and received data can be successfully characterized by several models, primarily by Hershel – Bulkley model. The ketchup was found to be a typical time-dependent thixotropic fluid. Shear stress and viscosity decrease with time of shear. Decrease during first 300 s is more significant than later decrease. The influence of spindle speed, shear rate potentially, on a sample viscosity was observed. The viscosity was rapidly changing during low speeds. The data were compared with Carreau model. Many other dependeces (low and high shear rates, difference between mixed and rested material etc.) were observed and modelled with satisfying results. Dependence of shear stress on shear rate under two temperatures was also examined. The tendency of increasing shear stress with increasing shear rate is evident. The samples were examined under temperature 22 °C and temperature 7 °C.