Rheological behaviour of acorn starch dispersions: Effects of concentration and temperature

Rheological properties of acorn starch dispersions at different concentrations (4%, 5%, 6% and 7%) were evaluated under steady and dynamic shear conditions. The flow behaviours of the acorn starch dispersions at different temperatures (25, 40, 55 and 70 °C) were determined from the rheological parameters provided by the power law model. The acorn starch dispersions at 25 °C exhibited high shear-thinning fluid characteristics (n = 0.23-0.36). Consistency index (K) and apparent viscosity (η_a,100) increased with an increase in starch concentration, and were also reduced with increasing temperature. Within the temperature range of 25-70 °C, the η_a,100 obeyed the Arrhenius temperature relationship with a high determination coefficient (R² = 0.97-0.99), with activation energies (E_a) ranging between 16.5 and 19.0 kJ mol^-1. Both the power law and exponential type models were employed in order to establish the relationship between concentration and apparent viscosity (η _a,100) in the temperature range of 25-70 °C. Magnitudes of storage (G′) and loss (G″) moduli increased with an increase in the starch concentration and frequency (ω). The magnitudes of G′ were higher than those of G″ over most of the frequency range (0.63-62.8 rad s^-1). The dynamic (η*) and steady shear (η_a) viscosities of acorn starch dispersion at 7% concentration follow the Cox-Merz superposition rule.