| A generalized model has been developed for predicting the extrudate viscosity of low to intermediate moisture content starch based products during cooking extrusion. The model incorporates the effects of shear rate, temperature, moisture content, time-temperature history and strain history.;The model was tested using doughs of potato flour, corn starch and whole wheat flour. Equipment used included an Instron Capillary Rheometer and a Baker-Perkins MPF 50 D/25 co-rotating twin screw extruder.;Experiments with potato flour were conducted at temperatures of 25, 50, 65, and 95;In potato dough, shear rate was described by the power law model. Time-temperature history and strain history did not influence viscosity. The final predictive model incorporates shear rate, temperature and moisture content and yielded an R;Corn starch dough moistures were 0.359, 0.476, and 0.572 g water per g starch for capillary rheometer tests and 0.5 and 0.6 g water per g solids in extrusion tests. Capillary rheometer barrel temperatures were 50, 55, 60, 75, 85, 95, and 110;Shear rate was modelled by the equation proposed by Ofoli et al. (1988). Corn starch viscosity was a function of cook temperature and moisture content, but not cook time. Predicted versus observed viscosities gave an R;Whole wheat flour moisture contents were 0.333, 0.337, 0.385, and 0.426 g water per g solids. Overall fit of the model improved with corrections for temperature, moisture, and time-temperature history. Cooked dough viscosity was a function of moisture, cook time and temperature. The fit (R... |
