OPTIMIZATION OF EXTRUSION COOKING PROCESS PARAMETERS TO DEVELOP TEFF BASED PRODUCTS

Abstract

This study aimed to develop nutritious and sensorially acceptable teff based expanded product using twin screw extruder through optimization of extrusion process variables. The experimental study was performed using response surface methodology Box Behnken design to investigate the effect of four independent variables: feed moisture content (15, 20, 25%), blend ratio of (10, 15 and 20% chickpea), barrel temperature (110, 130 and 150°C) and screw speed (150, 170 and 190 rpm) on products' functional properties (water absorption index and water solubility index), physical properties (expansion ratio, specific length), textural property (hardness) and sensory acceptability of extruded products. The extruder die opening was 9.00 mm diameters. The maximum expansion ratio (1.88 mm/mm) was obtained at 20% feed moisture content, 20% chickpea blend ratio, barrel temperature of 150 0C and 170 rpm screw speed., maximum Water Absorption Index (7.48 g/g) and maximum specific length (2.23cm/g) values of the extrudates were observed at 110 0C, 170 rpm, 25% feed moisture content and 15% chickpea blend ratio. The minimum density (0.22 g/cm3) was obtained at 150 0C, 170 rpm, 15% feed moisture content and 15% chickpea blend ratio and the maximum Water Solubility Index (22.5%) was obtained at 130 0C, 150 rpm, 15% feed moisture content and 15% chickpea blend ratio. Sensory acceptability evaluation of extrudate produced at 130oC barrel temperature, 20% feed moisture content 10% chickpea blend ratio and screw speed of 150 rpm were significantly (P<0.05) highest in color (6.30) , whereas those produced at 130oC barrel temperature, 20% feed moisture content 20% chickpea blend ratio and screw speed of 150 rpm were significantly (P<0.05) best in crispiness (6.55) and overall acceptability (6.15).The model developed could be used for designing of extrusion process conditions for getting extrudates with desirable physical characteristics. The optimum condition of feed moisture content 15%, blend ratio (20%chickpea), barrel temperature 150 0C and screw speed 170 rpm are recommended. In this study, promising results were obtained for teff- chickpea based extrudate development and process optimization.