Effects of screw speed on the structure and physicochemical properties of extruded reconstituted rice composed of rice starch and glutelin

Abstract

Reconstituted rice composed of rice starch and glutelin was prepared under varied screw speeds by a twin-screw extruder, and the structure and physicochemical properties were analyzed. When the screw speed ranged from 265 to 345 rpm, the expansion ratio and cooking loss of reconstituted rice separately increased from 219.20% and 6.30–238.40% and 11.50%, while the bulk density reduced from 2.39 to 1.27 g/mL accompanying the color became darker. The water solubility index of reconstituted rice changed insignificantly with increasing screw speed. Clusters of gelatinized starch granules were observed, and the inner structure of reconstituted rice became rough and cracked. Increasing screw speed was not conducive to maintaining the viscoelasticity of reconstituted rice pastes due to the decrease in pasting parameters, and their frequency dependence was lower than raw rice paste. The relative crystallinity of reconstituted rice decreased from 13.45% to 4.50% as the screw speed increased, resulting in corresponding changes in thermal properties. Furthermore, the texture of cooked reconstituted rice was closely associated to screw speed. This study supplies theoretical guidance for producing extruded reconstituted rice.