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

¹Agricultural and Biosystems Engineering, South Dakota State University, Brookings, SD, 57007, U.S.A. ²Agricultural and Biosystems Engineering, Iowa State University, Ames, IA, 50011, U.S.A. ³Corresponding author. Phone: (515) 294-4019. E-mail: karosent@iastate.edu ⁴Department of Natural Resources Management, South Dakota State University, Brookings, SD, 57007, U.S.A.

A twin-screw extrusion study was performed in replicated trials to produce vegetable-based feeds for juvenile yellow perch. Two isocaloric (3.06 kcal/g) experimental diets were balanced to contain 20 and 40% distillers dried grains with solubles (DDGS) and a constant amount (20%) of fermented high-protein soybean meal (PepSoyGen) as the fishmeal protein replacers; crude protein content was targeted at 40%. A fishmeal-based diet was used as a control. Extrusion conditions included 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, lightness L*), yellowness (b*), and unit density but to decreases in water activity (a_w) and expansion ratio by 12.6, 14.4, 23, 21, 31, and 13%, respectively. The lowest unit density of 791.6 kg/m³ and highest bulk density of 654.5 kg/m³ were achieved with diets containing 20 and 40% DDGS, respectively; changes in DDGS content did not affect extrudate moisture, absorption index, or thermal properties. Raising DDGS from 0 to 40% resulted in an increase in water solubility and redness (a*) by 13.4 and 35%, respectively. All extrudates had high durability (>98%), and low a_w of less than 0.5. Overall, this study yielded viable feeds for yellow perch.