Effect of Blend ratio and Extrusion Operating Conditions on Product Quality of Sorghum/Soybean Extrudate

In this work, the effects of full fat soybean flour addition and extrusion operating conditions (barrel temperature and feed moisture) on quality characteristics of sorghum flour extrudates were studied, with the objective of developing ready-to-eat extruded product. A pilot scale twin screw food extruder was used for the extrusion. Full factorial design was employed to investigate the effect of blend ratio (95:05, 90:10 and 85:15 sorghum and soybean respectively), barrel temperature (120, 135 and 150 °C) and feed moisture levels (14, 16 and 18%) on the physical (radial expansion ratio and bulk density) and functional (water absorption index and water solubility index) properties of the extrudates. Maximum radial expansion ratio (two times) and minimum bulk density extrudate was obtained at 90:10 blend ratio. In addition to this lower blend ratio (95:05) registered lower water absorption index and higher water solubility index. Taking into consideration the extrusion operating conditions, increasing barrel temperature (120-150 °C) and feed moisture (14-18%) decreased the radial expansion ratio and water solubility index while increasing the water absorption index. Later on, the results of the sensory evaluation (color, flavor, texture and overall acceptability) revealed that increased blend ratio, barrel temperature and feed moisture content decreased the level of acceptance yet the results also showed that the extruded product from 90:10 blend ratio, 120 °C barrel temperature and 14% feed moisture is still an acceptable product with an overall acceptability of 7.1. It was then demonstrated from the optimization result that it is possible to produce good extruded product. The extruded product from 91.8:8.2 (sorghum and soybean respectively), 120 °C barrel temperature and 14% feed moisture was selected as best formulation to yield a protein rich extruded product with desirable attributes like higher radial expansion ratio (2.02), lower bulk density (0.072), higher water absorption index (4.53) and higher sensory ...