Twin Screw Extrusion of DDGS-Based Aquaculture Feeds1

Six isocaloric (3.65 kcal/g), isonitrogenous (35% dry-basis [db] protein), ingredient blends were prepared with 0, 17.5, 20, 22.5, 25, and 27.5% distiller's dried grains with solubles (DDGS) and other ingredients (soybean meal, corn, fish meal, whey, soybean oil, vitamin and mineral mix). The blends were moisture balanced to 15% db, then extruded in a twin screw extruder using a 2 mm die at 190 rpm, and a 3 mm die at 348 rpm. Analyses of the extrudates included moisture content, expansion ratio, unit density, bulk density, sinking velocity, color (L *, a *, and b*), water absorption, water solubility, and pellet durability indices. Increasing the DDGS level from 0 to 17.5% db resulted in decreased expansion ratios by 14.8 and 23.5% for the products extruded using a 2 and 3 mm die, respectively. No significant difference in expansion ratio existed for DDGS levels between 17.5 and 27.5% db for either die. The water solubility index (WSI) of the extrudates increased (25.2 and 24.0%) as the DDGS increased from 0 to 27.5% db for each die. The 0% DDGS had the highest expansion ratio and the lowest unit density, bulk density, and sinking velocity. The extrudates that contained 20 and 27.5% DDGS had the highest durability and sinking velocity values.