Optimization of maize-millet based soy fortified composite flour for preparation of RTE extruded products using D-optimal mixture design.

Formulation of composite flour comprising of maize (MF), finger millet (FM), defatted soy (DS) and elephant foot yam (YP) was carried out for the preparation of extruded product. The proportion of three major ingredients was varied as maize: 40-55%, finger millet: 20-30%, defatted soy: 10-25% and that of YP was kept constant as 10%. In all 16 experiments were conducted by D-optimal mixture design keeping the upper and lower values of ingredients in the range given above. Extruded products were developed by using twin screw extruder (BTPL lab model) at barrel temperature 100 °C, screw speed 300 rpm and feed moisture content 15% (wb). Physical and functional properties like expansion ratio (ER), bulk density (BD), hardness, water absorption index (WAI) and water solubility index (WSI) of extruded products were analyzed. Composite flour was optimized on the basis of physical and functional properties of extruded products. The values of ER, BD, hardness, WAI and WSI of extruded products were in the range of 2.42-3.30, 0.14-0.26 g cm-3, 11.15-18.67 N, 5.57-6.87 g g-1 and 14.42-19.95%, respectively. Variations in proportion of ingredients in the composite blend significantly affected ER, BD, hardness, WAI and WSI of the product. The regression models for ER, BD, hardness, WAI and WSI were developed to explain the effect of ingredients on the response variables. A blend of ingredients in the ratio of 40:30:20:10 (MF:FM:DS:YP) was found to be optimum with a desirability function of 0.82 which resulted extrudate attributes of ER 3.29, BD 0.14 g cm-3, hardness 11.94 N, WAI 6.13 g g-1 and WSI 17.07%. © Association of Food Scientists & Technologists (India) 2020.