Effect of barrel temperature and screw speed on rapid viscoanalyzer pasting behaviour of rice extrudate

The effect of extrusion barrel temperature (80-120 degrees C) and screw speed (200-400 rpm) on the pasting and gelatinization properties of extruded rice products were studied. A twin-screw extruder was used without using a die. A rapid viscoanalyser (RVA) was used for the pasting study, the parameters determined were the initial viscosity (IV), peak viscosity (PV), hot-paste viscosity (HPV) and cold-paste viscosity (CPV). The PV, HPV and CPV generally decreased with increasing barrel temperature and screw speed. The IV was high, 30-43 rapid viscoanalyser units (RVU), for extrudates compared with raw rice, 3-4 RVU. The extent of gelatinization (GE) of the extruded rice samples ranged between 93.8% and 99.0%, and an increase in screw speed enhanced the CE values. Regression equations (r greater than or equal to 0.991, P less than or equal to 0.01) that relate pasting and gelatinization behaviour to temperature and screw speeds are reported.