Effect of Extrusion Conditions on Pasting Behavior and Microstructure of Refabricated Rice: A Response Surface Analysis

The effects of moisture, screw speed, and barrel temperature on pasting behavior of refabricated rice grains were investigated in a corotating twin-screw extruder with response surface methodology. The rice flour obtained from broken rice (<= 1/8 of actual kernel size) of PR-116 variety was used in the study. The screw speed was set at five levels between 49 and 150 rpm, barrel temperature between 59 and 110 degrees C, and feed moisture between 31 and 45%. All pasting properties of refabricated grains evaluated-peak viscosity, hold viscosity, breakdown viscosity, final viscosity, and setback viscosity-were significantly (P < 0.01) affected by the three process variables. Barrel temperature was the most significant variable, with quadratic effect on all viscosity parameters. Response surface regression models were established to correlate the viscosity profile of refabricated rice grains to the process variables. The optimum moisture content, screw speed, and barrel temperature estimated by a response surface of desirability function for the production of refabricated rice were 36%, 130 rpm, and 89.5 degrees C, respectively. Scanning electron microscopy also revealed that intermediate moisture and temperature along with high screw speed during extrusion could create a more realistic appearance of refabricated rice with less rupture of starch granules.