Effect of extrusion parameters on production process and expansion ratio of reformed rice

Response surface methodology (RSM) was used to study the effects of screw speed, feed rate, feed moisture content, and terminal barrel temperature on several system parameters (product temperature, die pressure, motor torque, specific mechanical energy and product moisture content) and physical properties (expansion ratio) of the reformed rice made by hybrid indica rice (type 9718). Second-order polynomials were used to model the extruder responses as a function of process variables. Die pressure, specific mechanical energy and expansion ratio were affected by all four process variables, while product moisture content was only influenced by feed moisture content. Product temperature was affected by all variables except for feed rate, and motor torque was affected by all variables except for terminal barrel temperature. Specific mechanical energy increased with screw speed increment, while feed moisture and terminal barrel temperature reduced with feed rate increment. The high correlation between the models and the measured data showed that the calculated second-order polynomials were sufficiently accurate and valuable tools in interpreting the multi-variable field of extrusion cooking of reformed rice.