SCREW CONFIGURATION EFFECTS ON STARCH BREAKDOWN DURING TWIN-SCREW EXTRUSION of RICE FLOUR

Abstract

Screw configuration effects on starch breakdown and ext rudate porosity were investigated during twin-screw extrusion of rice flour. the type, length, position, of mixing elements and spacing between two elements significantly affected molecular breakdown of starch in rice flour and extrudate porosity. Generally, screw profiles with reverse screw element produced more starch breakdown and porous extrudates than those with kneading block. A systematic increase of starch breakdown was observed as the mixing elements were moved fart her from the die, with longer elements, and with increased spacing between elements. Extent of starch breakdown affected porosity of extrudates. Extrudate porosity decreased systematically with increasing distance between die and mixing element, with larger spacing between the elements, and by moving two elements (with same spacing) farther from the die, irrespective of the element type and length. Porosity increased with increasing die temperature.