Effect of dietary fiber and screw speed on some extrusion processing and product variables

Yellow corn meals were extruded with wheat and oat fibers using an APV Baker MPF50/25 twin screw extruder. Increasing the screw speed from 200 to 300 rpm decreased percent torque, increased specific energy and decreased die pressure. The extrudates had increased axial expansion but decreased radial expansion, increased bulk density and breaking force. Adding either wheat fiber (up to 30%) or oat fiber (up to 20%) to corn meals had no appreciable effects on percent torque, specific energy and die pressure. Increasing fiber content in corn meals increased the axial expansion but decreased the radial expansion. The net results were increases in the bulk density and breaking force for the extrudates.