Modelling the Effects of Feed Moisture and Ingredient Variations on the Physical Properties and Functional Characteristics of Extruded Sorghum-Groundnut-Cowpea Blends using Response Surface Methodology

Central composite rotatable design for k = 3 was used to study the combined effect of feed moisture (12-44%), cowpea concentration (0-20%) and groundnut concentration (0-10%) on the physical and functional properties of extruded sorghum-legume blends in a single screw extruder using response surface methodology. Product expansion ratio, bulk density, total colour change, water absorption capacities at 27 degrees C and 90 degrees C and swelling capacities were determined on the products using standard analytical methods. Expansion ratio, bulk density and total colour of extrudates from the sorghum-legume blends decreased with increasing feed moisture. Increasing the concentration of legumes in the product increased the water absorption capacities at 27 degrees C and 70 degrees C and increased swelling capacities due to the gel forming ability of the macromolecules (proteins and starch) in the products and availability of hydrophilic groups to bind water molecules, thus enhancing the functional properties of the blends. Models developed for the indices gave R(2)-values ranging from 61.6% (for water absorption capacity at 27 degrees C) to 89.9% (for bulk density) with insignificant lack of fits indicating the adequacy of the model in explaining the data. The optimal conditions noted for producing the puffed extruded snack products with better physical properties and functional characteristics from sorghum-groundnut-cowpea blends were at 16-18% feed moisture, 14-16% cowpea and 6-8% groundnut additions.