EFFECT OF EGGSHELL ON PROPERTIES OF CORN STARCH EXTRUDATES

Corn starch was extruded in a single-screw laboratory extruder at 140 degrees C barrel temperature and 140 rpm screw speed. Expansion ration , bulk density, shear strength, percentages of closed and open pores, porosity, and molecular degradation of extruded starch were measured. Addition of up to 10% eggshell resulted in decreases in expansion rati o, bulk density, and percentage of open pores; and increases in shear strength, percentage of closed pores, and porosity of extrudates. Cros s-sections became smaller with a greater number of round and uniform-s ized cells for extrudates with added eggshell. Gel-permeation chromato graphy fractionation of starch extruded with eggshell showed extensive degradation of fraction I with increasing eggshell concentrations. Th e eggshell appeared to have provided nucleation sites for water vapori zation as the material exited the die of the extruder.