Shear-thickening behavior of gelatinized waxy starch dispersions promoted by the starch molecular characteristics

Abstract

An unusual shear-thickening behavior was observed in 10% w/w gelatinized waxy potato and waxy corn starch dispersions at shear rates around 20 s^-1. However, the phenomenon was not found in gelatinized dispersions of waxy rice. The aim of this study was to investigate reasons for the observed shear-thickening behavior as well as its relationship with the amylopectin molecular structure. This unique phenomenon only appears at a shear rate of about 20 s^-1 during the increasing shear rate stage of the first cycle of a two-cycle steady shear flow test. After 7 d storage, the shear-thickening behavior of waxy potato starch dispersions disappeared, while it remained in waxy corn starch dispersions. A small strain temperature sweep test applied to waxy potato starch dispersions stored for 7 d showed a significant increase in the elastic behavior of dispersions at temperatures lower than 60 °C. This behavior was not observed on fresh and 7 d stored waxy corn and waxy rice dispersions. The study provides valuable information on a unique rheological behavior of waxy starch dispersions and its relationship to the amylopectin structure, thus opening opportunities for the design of novel foods with desired nutritional and textural properties.

Keywords: Dispersion rheology; Gelatinized waxy starches; Retrogradation; Shear-thickening; Structural recovery.