INFLUENCE OF GRANULE SIZE ON VISCOSITY OF CORNSTARCH SUSPENSION

The influence of granule size and size distribution in gelatinized sus pensions of 2.6% cornstarch heated at fixed temperatures between 70-90 C on the power law viscosity was measured by laser diffraction. In the early stages of gelatinization, where the granule size standard devia tion was less than 12 mu m, dilatant behavior was observed over the sh ear rate range 200-1100 s(-1). At constant starch concentration and wi thout granule rupture, suspension consistency, K, increased exponentia lly with granule mean diameter while the flow behavior index, n, decre ased linearly with increase in the extent of gelatinization and the st andard deviation of the granule size. The variation of K with granule size and that of n with standard deviation were found to be independen t of temperature over 70-90C. In the later stages of gelatinization, w here the granules lose their integrity, suspension viscosity progressi vely decreased as granule rupture continued.