Millet–legume blended extrudates characteristics and process optimization using RSM

▶ RSM based designed experiments were conducted to prepare millet–legume extrudates. ▶ The feed MC had predominant effect upon SEI, WAI and crispness of the extrudates. ▶ Extrudate density was most susceptible to the variations of the extruder screw speed. ▶ Generated models were found to be statistically valid and suitable for predictions. ▶ Predicted values had non-significant ( p < 0.01) difference from experimental values. Designed experiments were conducted to prepare extrudates from different millet–legume blend ratios (BR) of varying moisture content (MC); the extruder was operated at varying die head temperature (DHT), barrel temperature (BT), and screw speed (SS). Second order polynomial models were developed using response surface methodology (RSM) to understand the effect of the variables on density, sectional expansion index (SEI), water absorption index (WAI) and crispness of extrudates. The MC had predominant effect upon SEI, WAI and crispness, while density was most susceptible to the variations in SS. All the models were found to be statistically valid. Optimum processing condition generated from the models was: MC, 23.2%w.b.; BR, 19.9%legume; DHT, 187 °C; BT, 121.1 °C and SS, 123 rpm. The predicted responses in terms of density, SEI, WAI and crispness were 0.52 kg/m 3, 5.1, 9.4 and 45, respectively. The predicted values registered non-significant ( p < 0.01) difference from experimental values.