Mechanisms of elastic turbulence in gelatinized starch dispersions

The aim of this work is to study the rheological response of gelatinized starch dispersions under constant shear stress. To this end, starch dispersions at four different starch concentrations, were prepared by stirring and heating at 90 °C by 20 min. The experiments showed that the mechanical (i.e., strain) response is composed by a long-term trend that can be described by a two-relaxation mode process, and a high-frequency unstable response. Optical images indicated that the compact packing of the insoluble amylose-rich material, known as ghosts, is responsible for the unstable flow response. In fact, after destroying the starch dispersion microstructure with severe shear conditions (sonication), it was observed that the unstable flow response was no longer present. Fourier and fractal (DFA) analyses showed that the scaling characteristics of the strain instabilities depend on the starch concentration and the applied shear stress value. Also, the characteristic flow curves suggested that yield stress and non-monotonous flow curves are at the center of the mechanisms triggering elastic turbulence in starch dispersions.