Twin Screw Extrusion of DDGS-Based Aquaculture Feeds

Abstract

Six isocaloric (3.65 kcal/g), isonitrogenous (35% db protein), ingredient blends were prepared with 0, 17.5, 20, 22.5, 25, and 27.5% DDGS and other common ingredients, including soybean meal, corn, fish meal, whey, soybean oil, and vitamin and mineral mix, in order to produce balanced rations appropriate for tilapia grower diets. The blends were moisture balanced to 15% db, and then extruded in a pilot-scale twin screw extruder. The extrusion process was carried out using two processing conditions: a 2 mm die at 190 rpm (with temperatures ranging from 80 to 110oC, depending on barrel location), and a 3 mm die at 348 rpm (with barrel temperatures ranging from 60 to 100oC). Analyses of the resulting 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. Processing parameters such as mass flow rate, and moisture content at the die were measured to quantify the behavior of the extruder. Increasing the DDGS level from 0 to 17.5% db resulted in decreased expansion ratio values 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, however. The WSI of the extrudates were found to increase substantially (25.2 and 24.0%) as the proportion of DDGS was increased from 0 to 27.5% db for each die, respectively. The extrudates that contained 0% DDGS (i.e. the control blend) had the highest expansion ratio and the lowest unit density, bulk density, and sinking velocity values, and could be used as a floating feed. The extrudates that contained 20 and 27.5% DDGS, on the other hand, had the highest pellet durability and sinking velocity values, which indicates that they could better resist mechanical damage during transportation and storage, but are more suitable for sinking feed, respectively.