Structural properties of extruded corn starch

Structural properties, such as apparent density, true density, expansion ratio and porosity, of extruded corn grits were measured. Corn grits were extrusion-cooked in a Prism extruder with varied feed rate (1.16-6.44 kg/h), screw speed (150-250 rpm), product temperature (100-260 °C) and feed moisture content (12-25 kg/100 kg wet basis). A simple mathematical model was used to correlate the examined properties with the extrusion conditions. Extruded product apparent density, porosity and expansion ratio were found to be dependent on feed moisture content, residence time and temperature while they were not affected by screw speed. More specifically, the apparent density of extruded products had an increasing trend with feed moisture content and residence time, while it decreased with product temperature. Porosity and expansion ratio of extruded products decreased significantly with feed moisture content and residence time, while temperature rise resulted in products of higher porosity and expansion ratio.