Effect of Die Dimensions on Extrusion Processing Parameters and Properties of DDGS-Based Aquaculture Feeds

The goal of this study was to investigate the effect of die nozzle dimensions, barrel temperature profile, and moisture content on DDGS-based extrudate properties and extruder processing parameters. An ingredient blend containing 40% distillers dried grains with solubles (DDGS), along with soy flour, corn flour, fish meal, whey, mineral and vitamin mix, with a net protein content adjusted to 28% was extruded in a single-screw laboratory extruder using seven different die nozzles. Increasing moisture content of the ingredient mix from 15 to 25% resulted in a 2.0, 16.0, 16.3, 22.9, 18.5, 32.5, and 63.7% decrease, respectively, in bulk density, water-solubility index, sinking velocity, L*, b*, mass flow rate, and absolute pressure, as well as 11.6, 16.2, and 7% increases, respectively, in pellet durability, water-absorption index, and a*. Increasing the temperature from 100 to 140°C resulted in 17.0, 5.9, 35.4, 50.6, 28.8, 33.9, and 33.9% decreases, respectively, in unit density, pellet durability, sinking velocity, absolute pressure, specific mechanical energy, torque, and apparent viscosity, but a 49.1 and 16.9% increase, respectively, in dough temperature and water-absorption index. Increasing the L/D ratio of the die nozzle resulted in an increase in bulk density, L*, a*, and torque, but a decrease in unit density, pellet durability, water-absorption index, sinking velocity, b*, mass flow rate, dough temperature, and apparent viscosity. As demonstrated in this study, the selection of an appropriate die geometry, in addition to the selection of suitable temperature and moisture content levels, are critical for producing DDGS-based extrudates with optimum properties.