Effect of extrusion conditions on expansion behavior and selected physical characteristics of cornstarch extrudates

Three response parameters (apparent density, porosity, and expansion ratio) were examined for investigating the expansion characteristics of cornstarch as a function of extrusion conditions. Cornstarch with moisture contents of 18.3%, 26.1%, and 34.8% (dry basis) were extrusion cooked in a twin-screw extruder at barrel temperatures of 120°C and 140°C and screw speeds of 200, 300, and 400 rpm. Results indicated that feed moisture content, barrel temperature, and screw speed had significant effects on the density, porosity, and expansion ratio of extruded cornstarch products (p < 0.05). Increases in feed moisture content resulted in increases in bulk density and decreases in porosity and expansion ratio (p < 0.05). Increases in barrel temperature and screw speed resulted in decreases in bulk density and increase in porosity and expansion ratio (p < 0.05). At a given screw speed and barrel temperature setting, apparent density and porosity exhibited linear dependencies on moisture content (R² ≥ 0.87 and 0.85, respectively). Moreover, the moisture content and surface temperature of the extruded products were influenced by extrusion conditions. Lowering the feed moisture content and increasing the barrel temperature and screw speed caused a lower moisture content and higher surface temperature of the cornstarch extrudates (p < 0.05). These results can be used to optimize the process conditions, which can minimize production loss and provide information for controlling or predicting textural characteristics of expanded cornstarch products.