Process variables during single-screw extrusion of fish and rice-flour blends

Extrusion cooking of fish and rice-flour blends in a single-screw cooking extruder was studied under a wide range of variables of barrel temperature, screw speed, fish content and feed-moisture content which ranged from 100 to 200C, 70-110 rev/min, 5-45% and 20-60%, respectively. Experiments based on rotatable design showed that the physical properties of expansion ratio, bulk density, hardness and water solubility index (WSI) were significantly affected by all the process variables except screw speed. Barrel temperatures greater than 180C and feed moistures less than 58% result in a steep increase in expansion ratio and a decrease in bulk density. At a fish content of 5% and feed-moisture content of less than 52.5%, the hardness values decreased. When the WSI is at 40-42 % of fish content and the feed-moisture content is less than 55%, a steep increase was noticed, but a maximum WSI value of 11.5% was observed at a fish content of 41.37% and a feed-moisture content of 35%.