Twin-screw Extrusion Processing of Vegetable-based Protein Feeds for Yellow Perch (Perca flavescens) Containing Distillers Dried Grains, Soy Protein Concentrate, and Fermented High Protein Soybean Meal

Changing to alternative protein sources supports production of more economic aquafeeds. Two isocaloric (3.06 kcal/g) and isonitrogenous (40% db) experimental feeds for juvenile yellow perch were formulated with incorporation of fermented soybean meal (FSBM) and soy protein concentrate (SPC), each of which were at two levels (0 and 20% db), along with constant amounts of high protein distillers dried grains (DDG) (~30% db), and appropriate amounts of other ingredients. Using a pilot scale twin-screw extruder, feed production was performed in two replications for each diet at conditioner steam levels of 0.11 to 0.16 kg/min, extruder water of 0.11 to 0.19 kg/min, and screw speeds of 230 to 300 rpm. The effects of SPC and FSBM inclusion on extrudate physical properties were compared with those of a control diet (which contained 20% fishmeal and ~30% DDG). Inclusion of 20% FSBM and 20%SPC resulted in a substantial decrease in unit density by 9.2 and 24%, but an increase in lightness, greenness, yellowness, and expansion ratio of the extrudates by 7, 27, 14, 7, 17, 34, 15, and 16.5%, respectively. SPC inclusion led to a considerable increase in water absorption, thermal resistivity, and thermal diffusivity by 17.5, 6.3, and 17.6%, respectively, whereas no significant change was observed for these properties with incorporation of 20% FSBM. Additionally, all extruded products had high durability. Taken together, using ~30% DDG with20% FSBM or20% SPC as alternative protein sources resulted in viable extrudates with properties appropriate for yellow perch production. A future study investigating the effect of extrusion processing conditions on the production of complete vegetable-based protein feeds for yellow perch species would be appropriate.