Rheological properties of selected hydrocolloids as a function of concentration and temperature

In this study, rheological properties of several food hydrocolloids (carrageenan, pectin, gelatin, starch and xanthan) were evaluated using a rotational viscometer at three concentrations (1-6%, depending on the type of hydrocolloid) and four temperatures (20, 40, 60 and 80 degreesC). Samples were subjected to a programmed shear rate increasing linearly from 0 to 300 s(-1) in 3 min, followed by a steady shear at 300 s(-1) for 10 min and finally a linearly decreasing shear rate from 300 s-1 to 0 in 3 min. Experiments were performed in duplicate. In general, the power law model fitted most of the experimental results. Xanthan gum and carrageenan (at 20 degreesC) were exceptions, characterized by a yield stress and hence the rheograms were fitted with the Herschel-Bulkley model. Furthermore, gelatin showed a Newtonian behavior. Three models (power, exponential and polynomial) were used to evaluate the concentration effect on apparent viscosity. Arrhenius model was used to describe the temperature effect. Among the samples, carrageenan showed the most temperature dependency and xanthan gum, the least. (C) 2001 Elsevier Science Ltd. All rights reserved.