Optimization of extrusion variables for the production of extruded snacks from mung bean (Vigna radiata) flour

Abstract

This study investigated the effects of temperature (70, 75 and 80°C), screw speed (130, 140 and 150 rpm) and feed moisture content (55, 60 and 65%) on the protein, expansion ratio, bulk density, water absorption capacity, lightness and hardness of mungbean extruded snacks. The Box Behnken design of Response Surface Methodology was used to generate seventeen experimental runs having different combinations of the process variables. Standard laboratory procedures were used to evaluate the six responses. The regression coefficients and the 3D surface plot that explored the relationship between the extrusion variables and the responses were developed. The extrusion variables were optimized by choosing the desired goal for the responses. The amino acid contents of the optimized snack were analyzed and the sensory acceptability was rated using a 9-point hedonic scale. The values of protein, expansion ratio, water absorption capacity, bulk density, lightness and hardness ranged from 16.27 - 17.08%, 1.55-1.90, 5.29-6.52 g/g, 0.19-0.40 g/ml, 22.59-30.70 and 199.93-256.64 N, respectively. An increase in temperature and screw speed significantly (p< 0.05) increased the expansion ratio and water absorption capacity of the snack while the bulk density, lightness and hardness of the snacks decreased. An increase in feed moisture significantly (p<0.05) increased the hardness, bulk density and lightness of the snack while the expansion ratio of the snacks decreased. The optimal processing condition obtained was temperature (75.59°C), screw speed (142.41 rpm) and feed moisture (55.74%). The optimized snack contained all the essential amino acids. The highest sensory score for the optimized snack was the taste (7.33) while the lowest was the colour (5.17). In conclusion, an organoleptically acceptable extruded snack was produced from mung bean using the optimized process condition.