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 examin ed. 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 ap parent 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 wa s found that the how behavior index, n, approaches unity (Bingham model) fo r most of the data. It was also found that as t(CTH) was increased, for a g iven glucose concentration, both yield stress, tau(0), and consistency coef ficient, 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 level s of glucose concentrations. In general, the presence of glucose resulted i n an increase in the apparent viscosity compared to that of glucose-free st arch dispersions. (C) 2000 Elsevier Science Ltd. All rights reserved.