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

In this study, rheological properties of several food hydrocolloids (carrag eenan, pectin, gelatin, starch and xanthan) were evaluated using a rotation al viscometer at three concentrations (1-6%, depending on the type of hydro colloid) and four temperatures (20, 40, 60 and 80 degreesC). Samples were s ubjected 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 wer e performed in duplicate. In general, the power law model fitted most of th e experimental results. Xanthan gum and carrageenan (at 20 degreesC) were e xceptions, characterized by a yield stress and hence the rheograms were fit ted with the Herschel-Bulkley model. Furthermore, gelatin showed a Newtonia n behavior. Three models (power, exponential and polynomial) were used to e valuate the concentration effect on apparent viscosity. Arrhenius model was used to describe the temperature effect. Among the samples, carrageenan sh owed the most temperature dependency and xanthan gum, the least. (C) 2001 E lsevier Science Ltd. All rights reserved.