Effect of temperature and concentration on the physical properties of watermelon pulp.

Density and viscosity are important physical properties since they are the properties most used in calculations involving fluid transport. The main objectives of the present study were to examine the rheological behaviour and determine the density of watermelon pulp at different temperatures (10, 20, 30, 40, 50 and 60 °C) and concentrations (8, 17, 26 and 35 °Brix) and to obtain models to describe the alterations in these physical properties as a function of temperature and concentration. A Searle concentric cylinder rheometer was used to study the rheological behaviour and the density was determined using pycnometers. The models used in this work were fitted by nonlinear regression. It was concluded that the watermelon pulp behaved as a pseudoplastic non-Newtonian fluid at all the temperatures and concentrations used and that the Ostwald-de-Waele model could be used to describe this behaviour. Models were found that described the simultaneous effect of temperature and concentration on the density and viscosity of watermelon pulp, and these could be very useful in the food industry.