Abstract

FThe extrusion and extrudate properties measured include expansion indices (or puff indices), bulk density, residence time, solid density, moisture content, maximum stress, water solubility index (WSI), water absorption index (WAI), extruder output, crispness and color. The ranges of the three variables considered were 100 – 160°C for barrel temperature, 100 - 200rpm for screw speed, and 15 – 25% for feed moisture content (w.b.). The density of extrudate measured varied between 176 and 1100 kg/m3 for the extrusion variables considered. The moisture content of the dry extrudate is between 6 and 7.5 %. From the experimental results, predictive equations were developed to relate the influence of processing parameters on the grain sorghum extrudate quality. Using Matlab computer software for the response surface diagram (RSD), it was discovered that the effect of screw speed on density is negligible. Temperature has a significant impact on the density of the extrudate and it has a curvilinear effect on extrudate density and at high temperature, its quadratic effect dominates. Specific Mechanical Energy (SME) is directly proportional to screw speed. Comparatively, the screw speed has dominating effects on SME while temperature had a small effect. The results of the taste panel on crispness and color show that the product extruded at the conditioned feed moisture content of 20% and barrel temperature of 150°C gave the best crispness and color quality. Keywords: Extrudate, food extrusion, response surface, sorghum.