Title: Effects of Processing Conditions on Single Screw Extrusion of Feed Ingredients Containing DDGS Authors
|Chevanan, Nehru - SOUTH DAKOTA STATE UNIV|
|Muthukumarappan, K - SOUTH DAKOTA STATE UNIV|
Submitted to: Food and Bioprocess Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 30, 2008
Publication Date: February 26, 2008
Citation: Chevanan, N., Rosentrater, K.A., Muthukumarappan, K. 2008. Effects of Processing Conditions on Single Screw Extrusion of Feed Ingredients Containing DDGS. Food and Bioprocess Technology. DOI 10.1007/s11947-008-0065-y. Interpretive Summary: Distillers Dried Grains with Solubles (DDGS), a feed coproduct from the fuel ethanol industry, has been shown to be a viable potential alternative protein source for aquaculture feeds. The goal of this project was to examine extrusion processing conditions for feed ingredient blends of DDGS using a laboratory-scale extruder. Aquaculture feed mixes used in this study exhibited shear thinning behavior for blends containing DDGS up to 40%. Increasing the DDGS content resulted in a higher mass flow rate and a decreased die pressure. The torque requirement for the ingredient mix containing 40% DDGS was high, which led to a high specific mechanical energy and apparent viscosity of the dough. The torque, specific mechanical energy and apparent viscosity decreased as screw speed increased. At higher temperatures in the barrel and the die, the viscosity of the dough decreased, which led to a decreased torque requirement and specific mechanical energy. Increasing the moisture content of the ingredient mix did appear to affect the extruder parameters as well. Follow up studies should examine extrusion processing of DDGS-based ingredients in more detail, and should aim to quantify the effect of processing parameters on resulting extrudate properties.
Technical Abstract: Distillers Dried Grains with Solubles (DDGS), a feed coproduct from the fuel ethanol industry, has been shown to be a viable potential alternative protein source for aquaculture feeds. To investigate this, three isocaloric (3.5 kcal/g) ingredient blends containing 20, 30, and 40% DDGS, with a net protein adjusted to 28% (wb), were prepared for use as Nile Tilapia feed. Extrusion processing was then conducted using three DDGS contents (20, 30, and 40%, wb), three moisture contents (15, 20, and 25%, wb), three barrel temperature gradients (90°C-100°C-100°C, 90°C-130°C-130°C, and 90°C-160°C-160°C), and five screw speeds (80, 100, 120, 140, and 160 rpm, using a single screw laboratory extruder. Several processing parameters, including mass flow rate, net torque required, specific mechanical energy consumption, apparent viscosity, and temperature and pressure of the dough inside the barrel and die, were measured in order to quantify the extrusion behavior of the DDGS-based blends. For all blends, as the temperature profile increased, mass flow rate exhibited a slight decrease, die pressure decreased, and apparent viscosity exhibited a slight decrease as well. Likewise, the net torque requirement, specific mechanical energy consumption, and apparent viscosity decreased as screw speed increased, but mass flow rate increased. Additionally, as moisture content increased, die pressure decreased. At higher temperatures in the barrel and die, the viscosity of the dough was lower, leading to lower torque and specific mechanical energy requirements. Increasing the DDGS content, on the other hand, resulted in a higher mass flow rate and decreased pressure inside the die. As demonstrated in this study, the selection of suitable temperature and moisture content levels are critical for processing DDGS-based ingredient blends.