A viscosity model was developed to study the influence of soy white flakes during extrusion of fish feed and the effect of extrusion processing parameters on mass flow rate, torque, specific mechanical energy and viscosity of dough inside a single screw extruder were evaluated. Full factorial design was used for three variables each at three levels which generated total 27 experimental runs. Round capillary die rheometer was used to determine the rheological data of the dough within the extruder. It was observed that increase in the soy white flakes content resulted in a higher mass flow rate, torque and specific mechanical energy and a decrease in the apparent viscosity. The specific mechanical energy, mass flow rate increased and viscosity decreased with increase in screw speed. Higher barrel and die temperature led to decrease in the apparent viscosity of the dough, torque and specific mechanical energy. The viscosity model developed in this study can be applied to develop large‐scale extrusion models to determine the effect of soy white flakes on the feed material extrudates.
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