Optimization of extrusion process for production of expanded product from green gram and rice by response surface methodology

Abstract

Response surface methodology (RSM) was employed to study effect of feed moisture and metering zone temperature on physical properties of green gram extrudate. Temperature and moisture had significant effect on expansion ratio, which decreased with increasing moisture content. Feed moisture and die head temperature had negative effect on water holding capacity. Specific mechanical energy (SME) for extrusion and pressure developed at die head increased with increasing proportion of green gram in rice-green gram blend. With increase in barrel screw speed, viscosity of rice-green gram dough decreased resulting lesser power consumption and developed pressure at die head. During extrusion cooking, two important reactions (protein denaturation and starch gelatinization) in dough can affect viscosity. Rapid rise in starch viscosity is also a function of temperature, so that higher range of extrusion temperature and extrudate slurry viscosity caused high-pressure drop, which caused greater expansion of green gram extrudates.