Effect of glucose concentration on the rheological properties of wheat-starch dispersions

The effect of glucose addition and time of constant temperature heating (t(CTH)) on the rheological properties of starch dispersion systems was examined. A fixed starch mixture of 5% (w/v), and glucose concentrations of 0-6% (w/v) were used. The starch dispersion was heated up to 80 degrees C, then was kept, at this temperature, for a period of 0, 10, 20, or 30 min. The apparent viscosity was then measured as a function of shear rate. In addition, the apparent Viscosity was measured, at constant shear rate of 106 s(-1), as a function of shearing time. The Herschel-Bulkley model (tau = tau(0) + m gamma(n)) was used to fit the flow behavior of starch dispersions. It was found that the how behavior index, n, approaches unity (Bingham model) for most of the data. It was also found that as t(CTH) was increased, for a given glucose concentration, both yield stress, tau(0), and consistency coefficient, m, increased. The presence of glucose also resulted in an increase of both tau(0) and m. At 6% glucose concentration, samples with t(CTH) of 30 min showed the highest anti-thixotropic behavior. The apparent viscosity of starch dispersions at t(CTH) of 0 min had the lowest value at all levels of glucose concentrations. In general, the presence of glucose resulted in an increase in the apparent viscosity compared to that of glucose-free starch dispersions. (C) 2000 Elsevier Science Ltd. All rights reserved.