Twin-screw Extrusion Processing of Vegetable-Based Yellow Perch (Perca flavescens) Diets Containing Fermented High Protein Soybean Meal and Graded Levels of Distillers Dried Grains with Solubles

A pilot-plant twin screw extrusion study was performed in two twice-replicated trials with the goal of producing vegetable-based protein feeds for juvenile yellow perch. Two isocaloric (3.06 kcal/g) experimental diets were balanced to contain 20% and 40% DDGS, and a constant amount (20 %) of fermented high protein soybean meal (PepSoyGen, PSG), as the fishmeal protein replacers, in combination with appropriate amounts of other required ingredients; crude protein content was targeted at 40 %. A fishmeal-based diet was used as a control. To obtain cohesive extrudates, extrusion processing conditions were varied, including conditioner steam (0.11-0.16 kg/min), extruder water (0.11-0.19 kg/min), and screw speed (230-300 rpm). Increasing DDGS from 0 to 40% led to a considerable rise in bulk density, L*, b*, and unit density, but to a decrease in aw and expansion ratio by 12.6, 14.4, 23, 21, 31, and 13 %, respectively. Compared to the control diet, the lowest unit density and the highest bulk density of 791.6 kg/m3 and 654.5 kg/m3 were achieved with the diets containing 20 and 40% DDGS, respectively; changes in DDGS content did not affect the extrudate moisture content, absorption index, or thermal properties. Raising DDGS content from 0 to 40% resulted in a curvilinear increase in water solubility and a* of the extrudates by 13.4 and 35%, respectively. All extrudates had high durability of more than 98%, and low aw of less than 0.5. Overall, this initial study yielded physically viable feeds for yellow perch. Further extrusion studies are needed to determine optimal DDGS-based diet for yellow perch.