Response Surface Methodology for Studying the Effects of Feed Moisture and Ingredient Variations on the Chemical Composition and Appearance of Extruded Sorghum-Groundnut-Cowpea Blends

Abstract

Studies were conducted to evaluate the effects of feed moisture and ingredient variations on the chemical composition and appearance 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 to 44 percent), groundnut concentration (zero to 10 percent) and cowpea level (zero to 20 percent) on the chemical composition and appearance of extruded ready-to-eat sorghum-legume blends in a single screw extruder. Product moisture, crude protein, crude fat, ash (minerals), crude fibre, carbohydrate and colour (L, a and b-values) were determined on the products using standard analytical methods. The results showed that irrespective of the feed moisture level, the extrusion process could reduce the product moisture to levels between six to 10 percent and low enough to extend the shelf life of the derived products. Increasing additions of cowpea and groundnut resulted in significant increases in protein, fat and ash (minerals - calcium, iron, and phosphorus) contents of the sorghum-legume extrudates. Increasing addition of cowpea decreased the redness of the sorghum extrudates, while no changes were noted with groundnut additions. Contrary, increasing groundnut addition generally increased the yellowness at all cowpea concentrations, while only minimal changes were noted with cowpea additions. The lightness of the sorghum extrudates decreased with increasing cowpea and groundnut concentrations, and this was more pronounced at higher cowpea concentrations and with increasing groundnut levels. The level of feed moisture showed no effect. Models developed for the indices gave R2-values ranging from 67.04 percent (for a-value) to 87.83 percent (for fat content), with insignificant lack of fits indicating the adequacy of the model in explaining the data. The optimal conditions likely to produce ready-to-eat puffed snack with enhanced nutritive value and appearance from sorghum-groundnut-cowpea blend extrudates was at low feed moisture (10 to 14 percent), cowpea level (18 to 20 percent) and groundnut level (six to eight percent).