ABSTRACT
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%.
ABSTRACT
Moisture sorption behaviour and isosteric heat of sorption are essential to be familiar with the stability of products, various storage condition and selection of packaging materials. Sorption behavior of extruded product was done at 30, 40, 50 and 60 °C temperatures under 11-92% relative humidity. The product was developed from an optimized blend of maize, defatted soy, finger millet and yam at an optimum condition of 14% (wb) feed moisture, 110 °C barrel temperature and 301 rpm screw speed. The net isosteric heat of sorption of the extruded product was determined by using Clausius-Clapeyron equation. The equilibrium moisture content (EMC) was found to be raised with the rise in water activity (aw) in particular temperature. The highest EMC 30.05% (db) was recorded at 0.92 aw and 30 °C temperature, whereas the lowest EMC 2.46% (db) at 0.11 aw and 60 °C temperature. The isotherms exhibits curves of Type-II for four temperature conditions. The EMC data were fitted to six sorption models and GAB model was found to be best fitted among them. The net isosteric heat of sorption varied between 16.711 and 3.242 kJ/mol within 5-30% (db) of sample moisture content.
