Rheological behavior of heated starch dispersions in excess water: Role of starch granule

Granule size and size distribution, measured by laser diffraction, affected the flow behavior at 20°C of (2.6% w/w) corn and cowpea starch dispersions heated for various time intervals above their gelatinization temperatures. The standard deviation of the granules' size described the transition of flow behavior from shear thickening in the early stages of gelatinization to shear thinning in the latter stages and influenced the critical shear rate, γ̇_c, for the onset of shear thickening in starch dispersions. The granules swelled to a maximum of about 3·5 times the raw starch granule mean diameter and 65% granule mass fraction. The consistency index of the dispersions increased with granule mean diameter. Modified waxy maize starch dispersions heated at 80°C exhibited antithixotropic behavior at a shear rate of 200 s^-1; both dynamic frequency data and Cox-Merz plots revealed their gel-like behavior.