Screw configuration effects on corn starch expansion during extrusion

Normal corn starch was extrusion cooked in a Brabender single-screw extruder. Three screws with no mixing, one mixing or two mixing elements were used to extrude the samples through a 3 mm cylindrical die nozzle at 140 degrees C barrel temperature and 140 rpm screw speed. Dependent variables included overall and radial expansion ratios, bulk density and specific mechanical energy (SME). Extrudates were ground and re-extruded using the same three screws, and the same extrusion conditions. Significant differences (P 0.05) in bulk density, SME and radial expansion ratio were found on re-extrusion. No changes occurred in overall expansion ratio (P 0.05)