ARS | Publication request: Effect of DDGS, Moisture Content, and Screw Speed on the Physical Properties of Extrudates in Single Screw Extrusion

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 28, 2007
Publication Date: April 25, 2008
Citation: Chevanan, N., Rosentrater, K.A., Muthukumarappan, K. 2008. Effect of DDGS, Moisture Content, and Screw Speed on the Physical Properties of Extrudates in Single Screw Extrusion. Cereal Chemistry. 85(2):132-139.

Interpretive Summary: Aquaculture feed is a potential use for DDGS, but to date has not been thoroughly explored. Three feed blends were formulated to contain 3.5 kcal/g and 28% (wb) protein, and contained 20, 30, and 40% (wb) DDGS. The blends also contained soy flour, corn flour, fish meal, mineral and vitamin mix, in order to produce balanced feed rations. These blends were extruded in a single screw, laboratory-scale extruder at speeds of 100, 130, and 160 rpm, and 15, 20 and 25% (wb) moisture content. We found that increasing DDGS content from 20 to 40% resulted in a 37.1, 3.1, and 8.4% decrease in extrudate durability, specific gravity, and porosity, respectively, but a 7.5% increase in bulk density. We also found that increasing screw speed from 100 to 160 rpm resulted in a 20.3 and 8.8% increase in durability and porosity, respectively, but a 12.9% decrease in bulk density. On the other hand, we found that increasing the moisture content from 15 to 25% (wb) resulted in a 28.2% increase in durability, but an 8.3 and 8.5% decrease in specific gravity and porosity, respectively. Furthermore, we found that increasing the screw speed and moisture content of the blends resulted in an increase of 29.9 and 16.6% in extruder throughput, respectively. Increasing the DDGS content from 20 to 40% resulted in a 52.9 and 51.4% increase in fiber and fat content, respectively, and a 7.2 % decrease in Nitrogen Free Extract. As demonstrated in this study, ingredient moisture content and screw speed affect both processing conditions, as well as final extrudate quality.

Technical Abstract: Three isocaloric (3.5 kcal/g) ingredient blends containing 20, 30, and 40% (wb) DDGS along with soy flour, corn flour, fish meal, mineral and vitamin mix, with the net protein adjusted to 28% (wb) for all blends, were extruded in a single screw laboratory-scale extruder at screw speeds of 100, 130, and 160 rpm, and 15, 20 and 25% (wb) moisture content. Increasing DDGS content from 20 to 40% resulted in a 37.1, 3.1, and 8.4% decrease in extrudate durability, specific gravity, and porosity, respectively, but a 7.5% increase in bulk density. Increasing screw speed from 100 to 160 rpm resulted in a 20.3 and 8.8% increase in durability and porosity, respectively, but a 12.9% decrease in bulk density. On the other hand, increasing the moisture content from 15 to 25% (wb) resulted in a 28.2% increase in durability, but an 8.3 and 8.5% decrease in specific gravity and porosity, respectively. Furthermore, increasing the screw speed and moisture content of the blends, respectively, resulted in an increase of 29.9 and 16.6% in extruder throughput. The extrudates containing 40% DDGS had 8.7% lower brightness, as well as 20.9 and 16.9% higher redness and yellowness, compared to the extrudates containing only 20% DDGS. Increasing the DDGS content from 20 to 40% resulted in a 52.9 and 51.4% increase in fiber and fat content, respectively, and a 7.2 % decrease in Nitrogen Free Extract. As demonstrated in this study, ingredient moisture content and screw speed are critical considerations when producing extrudates with ingredient blends containing DDGS, as they are with any other ingredients.