Effects of Ingredients and Extrusion Parameters on Properties of Aquafeeds Containing DDGS and Corn Starch

Isocaloric (3.05 kcalg-1) ingredient blends were factorially formulated using 3 levels each of DDGS (20, 25 and 30% db), protein (30, 32.5 and 35% db) and feed moisture content (25, 35 and 45% db), along with appropriate quantities of corn starch, soybean meal, fish meal, whey, vitamin and mineral mix to produce a balanced diet for tilapia feed. The ingredient blends were extruded using a laboratory-scale single screw extruder with varying screw speeds (100, 150 and 200 rpm) and extruder barrel temperatures (100, 125 and 150°C). The resulting extrudates were subjected to extensive analyses of physical properties, which included moisture content, unit density, bulk density, expansion ratio, sinking velocity, water absorption, water solubility, color (L*, a* and b*) and pellet durability indices. Several extruder parameters, including moisture content at the die, apparent viscosity, specific mechanical energy, mass flow rate, net torque and die pressure were measured to quantify the extruder behavior during processing. All the formulations and process settings used produced viable extrudates, but some were of better quality than others. For example, increasing the DDGS levels from 20-25% db, protein content from 30-32.5% db, feed moisture content from 25-35% db, processing temperature from 100-125°C and screw speed from 100-150 rpm significantly increased the PDI values by 28.1,18.1, 31.8, 6.6 and 32.2%, respectively all of these curvilinearly decreased as these independent variables increased to their highest levels. Increasing the feed moisture content from 25-45% db resulted in a curvilinear increase in SME values by 69.3%. On the other hand, increasing the screw speed from 100-200 rpm curvilinearly decreased the SME values by 37.9%. This study highlights the importance of experimentally determining the effects of feed ingredients and process variables when developing aquafeeds from novel materials.