Influence of of extrusion variables on some functional properties of extruded millet-soybean for the manufacture of ‘fura’: A Nigerian traditional food

Abstract

‘Fura’ is a traditional thick dough ball snack produced principally from millet or sorghum which is common in Northern Nigeria. It is consumed with ‘nono’ (local yoghurt produced from cow milk) or mashed in water before consumption in the form of porridge. The effects of extrusion conditions feed composition (ratio of soybean to millet), percentage moisture wet basis and screw speed (rpm) on the water absorption index (WAI); water solubility index (WSI) and viscosity from millet/soybean flour mixtures were studied using Response surface methodology (RSM) for ‘fura’ processing. Models were developed and appropriate statistical analysis adopted to test the adequacy of the models. The models showed R2 = 0.73, 0.76, 0.74 for WAI, WSI and viscosity, respectively, indicating that the model could be used to navigate the design space. Because some of the stationary points were outside the range of the experiment, graphical optimization was adopted to determine the optimum and predicted values. The optimum levels and the corresponding predicted values were obtained. The optimal combination of feed composition (17.7% soybean), feed moisture (27.3% wet basis) and screw speed (161 rpm) resulted in optimal WAI of 4.6 g water per g sample. The optimal combination of feed composition (14.77% soybean), feed moisture (15.23%) and screw speed 220 rpm) resulted in optimal WSI of 6.15%. The optimal combinations of feed composition (46.97%), feed moisture (29.34%) and screw speed (174.52 rpm) resulted in optimal viscosity of 4.58 Nsm-2. Key words: Millet, soybean, extrusion, optimization, ‘fura’, water absorption index, water solubility index, viscosity.