Rheological Properties of Pastes Obtained from Starches Derived from Immature Cereal Kernels

The results presented in this work concern the starches of three basic varieties of cereal cultivated in Poland – wheat, rye and barley – harvested at different stages of maturity in 1997 and 1998. Starches from these kernels were isolated by a laboratory method. The flow curves and thixotropic properties of 5% starch pastes at 50°C and controlled shear rates between 0 and 600 s −1 were obtained. All the investigated starch pastes were non‐Newtonian, plastic and thixotropic fluids, that differed in their values of yield stress. The pastes from immature cereal starches were characterised by a higher plasticity because they needed a higher shear stress (τ) to achieve the yield stress (τ 01 ) in comparison with the pastes from the mature cereal starches. At applied shear stress the pastes from the “immature” starches had a higher thixotropy in comparison with the “mature” ones. Pastes from immature starch were more susceptible towards shearing forces but at the same time they exhibited a better ability to rebuild their structure. The description of the flow curves by the Ostwald‐de Waele equation allows the conclusion that pastes from the immature starches have a higher structural viscosity. In addition, the application of the Casson model allows to describe the flow curves and determine the yield stress and the plasticity properties of the investigated pastes. However, the viscosity values calculated from the Casson model do not reflect differences in viscosity among the samples.