DESIGN, FABRICATION AND PERFORMANCE EVALUATION OF A GROUNDNUT CAKE EXTRUDER WITH VARIABLE DIE GEOMETRY

Abstract

Groundnut cake (kulikuli) is a protein-rich snack widely consumed in Nigeria, but its traditional production methods are labor-intensive, unhygienic and unsuitable for large-scale processing. This study presents the design, fabrication and performance evaluation of a locally developed groundnut cake extruder equipped with variable die geometry. A single-screw extruder was designed and fabricated using locally available materials and fitted with three interchangeable die shapes: circular, square and inverted (which is a die whose opening is shaped in a reversed orientation influencing the shape and physical properties of the extruded groundnut cake). A randomized experimental design was employed to evaluate the effects of screw speed (7 rpm, 9 rpm and 11 rpm), moisture content (5.04%, 7.04% and 10.65%) and die shape on extrusion performance and product quality. Statistical analysis was carried out using Response Surface Methodology (RSM) and Analysis of Variance (ANOVA). Results indicated that screw speed, moisture content and die shape significantly influenced extrusion capacity, bulk density, expansion ratio and specific length of the extrudates (P < 0.05). Model adequacy and predictive capability were confirmed using coefficients of determination (R² ≥ 0.60), adjusted and predicted R², adequate precision ratios and error analysis parameters. The extruder recorded an average extrusion capacity of 12.30 kg/h with high extruding and cutting efficiencies. Optimum performance was achieved at a screw speed of 9 rpm, moisture content of 7.04%, and circular die shape, which produced groundnut cake with relatively low bulk density, improved expansion ratio, uniform shape and stable extrusion flow. The results demonstrate that the designed and fabricated machine is suitable for hygienic, efficient and 
small-to-medium scale production of groundnut cake.