The optimization of extrusion condition of Phatthalung Sungyod rice extrudate: a preliminary study

Phatthalung Sungyod rice flour was supplied to extrude in a co-rotating twin screw extruder. The effects of extrusion conditions such as, barrel temperature (135-165oC), screw speed (300-400 rpm) and feed moisture contents (12.5-17.5%) on physicochemical properties of rice extrudate and the optimized condition were studied by the use of response surface methodology (RSM). The second-order polynomials were used to model the product response as a function of process variables and the multiple regression equations were obtained to describe effect of each variable on product responses. Barrel temperature, screw speed and feed moisture content had significant effects on density, expansion ratio, water absorption index (WAI), water solubility index (WSI) and hardness of rice extrudate. They were most affected by the changes in the level of feed moisture content and barrel temperature. At low feed moisture content and high temperature, rice extrudate appeared to be expanded with low density and more crispness. WAI and WSI of extrudate increased with increase barrel temperature and decrease feed moisture content. The hardness of rice extrudate varied between 23.31 and 54.24 N. At the highest feed moisture content, the lowest barrel temperature and screw speed, the highest value of product’s hardness was obtained. The optimized extrusion condition for produced rice extrudate was at low feed moisture (12.5%), low screw speed (300 rpm) and high barrel temperature (165oC). With this condition, the well expansion, low product density and more crispness of extruded snack were obtained.