Protein Enriched Multigrain Expanded Snack: Optimization of Extrusion Variables

In the present study, effect of extrusion variables was evaluated on physical properties of multigrain extrudates. Experiments were designed using central composite rotatable design with independent variables i.e. feed moisture (14–18 % wb), die head temperature (90–110 °C), and screw speed (330–350 rpm). Six responses viz. Expansion ratio (ER), water absorption index (WAI), water solubility index (WSI), bulk density (BD), hardness and overall sensory acceptability were analyzed to obtain optimized extrusion parameters. ER, WAI, WSI, BD, hardness and overall sensory acceptability ranged from 2.64 to 3.18, 3.74 to 5.22 g/g, 20.92 to 45.37 %, 87.14 to 158.90 kg/m3, 23.27 to 68.17 N and 7.1 to 8.2, respectively. Feed moisture had significantly (p < 0.001) negative correlation with ER, WAI, WSI and overall acceptability and positive with BD and hardness. Effect of die head temperature was opposite to that of feed moisture on various physical parameters. ER, WSI and overall acceptability increased with increasing screw speed. Based upon multiple response optimization, optimized conditions were feed moisture: 14 %; die head temperature: 110 °C; and screw speed: 342.4 rpm (342) with maximum desirability (0.93). Protein, calcium and iron in the optimized sample were 15.5 %, 116.6 mg/100 g and, 4.3 mg/100 g, respectively.