An initial investigation into the inclusion of soy white flakes (SWF) and high protein distillers dried grains (HP-DDG) in catla (Catla catla) diet, belonging to the family Cyprinidae, was conducted using a single screw extruder. Three isocaloric (302 kcal/100 g) ingredient blends containing graded levels of SWF in combination with HP-DDG and other required ingredients were formulated to contain a net protein content of 31.5% (wet basis). Extrusion processing was then performed using three levels each of SWF content, moisture content, and temperature gradient keeping a constant screw speed and die diameter. Effects of these variables on extrudate physical properties including: color, pellet durability index, bulk density, water absorption index, water solubility index, unit density and expansion ratio were extensively analyzed. Increasing the level of SWF resulted in increase in water absorption index and unit density but decrease in expansion ratio. The interaction effect of SWF content, moisture content and temperature were significant for color, pellet durability index, bulk density and expansion ratio. All the extrudates showed relatively high pellet durability and inclusion of SWF produced less expanded and more compact textured extrudates.
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