Eefect of Extrusion Variables on Torque, Specific Mechanical Energy,Volumetric Flow Rate and Residence Time of Blends of mAcha/Soybean- A Response Surface Analysis

Soybean was sorted, washed, cracked, winnowed and coarsely milled in attrition mill. Acha grains were winnowed and milled similarly. Milled flours were sieved to pass 0.75-1 mm laboratory mesh. The Moisture content of the flours was determined. Soybean flour was added to acha flour at 0, 12.5, 25, 37.5 and 50% levels of substitution. The moisture content of the blends was then adjusted to 15, 20, 25, 30 and 35% levels. The flours were then re-mixed manually and allowed to equilibrate for 3 h. Extrusion was carried out using a Brabender laboratory single-screw extruder (Duisburg DCE -330 model). The screw speed was adjusted from 90 to 120, 150,180 and 210 rpm. The first and second barrel heaters were kept constant at 125 C while the exit heater was adjusted from 100, 125, 150, 175 and 200 C. Acha flour was used to stabilize the extruder before extrusion runs began. Extrusion was carried out following a four variable response surface analysis using a central composite rotatable design that was nearly orthogonal. During extrusion runs, the torque, the residence time and volumetric flow rates of extrudates were obtained. Specific mechanical energy was calculated from the data of torque and volumetric flow rate. The results showed that the torque ranged from 1.33 to 57(NmS) while volumetric flow rate ranged from (10-178 kg S 1). Similarly the specific mechanical energy ranged from (1.76-9.60 KW h 1) while the residence time ranged from (16.23-33.02 sec). The results were indicative that the second other polynomial was not adequate to model the dependence of the torque and specific mechanical energy on the process variables but modelled the dependence of the volumetric flow rate and residence time.