Effect of Talc on Properties of Corn Starch Extrudates

Commercially available 0, 25, 50 and 70% amylose corn starches were extruded with up to 5% talc {(OH) 2 Mg 3 (Si 2 O 5 ) 2 } in a single screw Brabender laboratory extruder at 18% moisture content, 140°C barrel temperature, and 140rpm screw speed. Expansion ratio, unit density, percentages of closed and open pores, porosity and molecular degradation of extruded starches were measured. Addition of talc resulted in decreases in expansion ratio, unit density and percentage of open pores, and in increases in percentage of closed pores and porosity of extrudates. The extrudates became smaller with a greater number of round and uniformly sized cells with added talc. Gel permeation chromatographic fractionation of extrudates showed extensive degradation of fraction I with increasing talc concentrations. The talc appeared to have provided nucleation sites for water vaporization as the material exited the die of the extruder.