Rheological properties of starch suspensions using a rotational rheometer fitted with a starch stirrer cell
Résumé
The rheological properties of a starch suspension are usually studied through two viscosity measurementspasting behavior and flow behavior of the resulting starch pastes-performed separately with two different tools and demanding rather high starch concentrations (6-10 wt %). This study focused on the feasibility of using a rheometer fitted with a starch stirrer cell to characterize, in a single experiment, the starch suspension's behavior during and after pasting, all the while involving only low concentrations (2-4 wt %), more representative of a real-food context. A calibration of the starch stirrer cell in comparison to the coaxial cylinders one was done using model fluids (Newtonian and shear-thinning). A link between torque, rotational speed, and rheological properties was determined through two recalculated conversion factors (shear rate and shear stress). An operating diagram was then set indicating the laminar flow and good sensitivity domain for this cell. The accuracy of those constants to starch suspensions in the concentration range 2-4 wt % was demonstrated. The pasting behaviors of 2 wt % starch suspensions were followed successfully at two selected shear rates (13.5 and 135 s−1). The impact of the level of turbulence on the profiles obtained was stressed, a result that is not limited to low-concentration starch suspensions. Finally, the method developed was used to compare the pasting behaviors of 2 wt % native and modified waxy maize starch suspensions.