Optimization of twin-screw extrusion process to produce okara-maize snack foods using response surface methodology

Okara-maize flour blends were extruded in a co-rotating twin-screw extruder in order to assess their suitability as snack foods. Response surface methodology (RSM) using a central composite design was used to evaluate the effects of process variables (extrusion temperature (120-180 degrees C), screw speed (100-180 rpm) and feed composition (20-40 percent ww) and moisture content (14-22 percent ww)). Multiple regression equations were developed to describe the effects of each variable on product responses. The product characteristics such as bulk density, expansion index, appearance (colour, porosity), flavor (aroma, grittiness and off-odor), texture (hardness, crispness and brittleness) and overall acceptability were determined through experiments and sensory analyses. Through superimposed RSM contour map, it was found that the feed composition with 30 percent okara content, 14.5-19.3 percent moisture content and the extrusion temperature 120.0-171.2 degrees C and screw speed of 140 rpm, respectively to be the optimum extrusion conditions. The sensory tests showed that the products extruded at the optimized condition had the best appearance, taste, texture and overall acceptability. These results show that the okara-maize blends can be extruded into acceptable snack foods.