1989 Volume 17 Issue 2 Pages 123-131
The rheological properties of white sauce (based on wheat starch) and several starch pastes were investegated.
Calculation of the rigidity of white sauce was made by using Lin's equation. The yield stress of white sauce was investigated by three methods. It was shown that the rheological properties of white sauce was plastic flow with rigidity and yield stress, and also was shear thinning flow. By cooking, temperature of the white sauce changes from 60°C to 20°C, and the yield stress was increased remarkably. The apparent activation energy for flow of white sauce was estimated as 4.52 kcal/mol.
The flow hysteresis curves for potato starch pastes were classified into three patterns, and the respective thixotropic parameters Th were calculated from the hysteresis loops. Values of the consistency index K, the flow behavior index n and the thixotropic coefficient λ were able to be determined from the curves of shear stress versus time under constant shear rate. The potato starch paste heated at 80°C exhibited thixotropy (softening for shear), and that heated at 98°C for 2 min showed negative thixotropy (hardening for shear). The spinnability of potato starch pastes was found to be related to the relaxation time τ for the samples if the samples showed similar values of the dynamic viscosity η′. Consequently, a linear relationship could be obtained between the spinnability and the product of η′ and τ for the potato starch pastes.
Changes in the dynamic properties of starch pastes were followed during a short span aging (0-2 hr) at 25°C. Based upon the relationship between the dynamic modulus and the mechanical loss tangent of the samples paste, it was interpreted that sol-gel transition of the system occurs at a region where dynamic modulus and mechanical loss tangent are about 1.75×102(dyn/cm2) and about 0.45, respectively.