No abstract

The goal of this study was to investigate the effect of die nozzle dimensions, barrel temperature profile, and moisture content on DDGS‐based extrudate properties and extruder processing parameters. An ingredient blend containing 40% distillers dried grains with solubles (DDGS), along with soy flour, corn flour, fish meal, whey, mineral and vitamin mix, with a net protein content adjusted to 28% was extruded in a single‐screw laboratory extruder using seven different die nozzles. Increasing moisture content of the ingredient mix from 15 to 25% resulted in a 2.0, 16.0, 16.3, 22.9, 18.5, 32.5, and 63.7% decrease, respectively, in bulk density, water‐solubility index, sinking velocity, L*, b*, mass flow rate, and absolute pressure, as well as 11.6, 16.2, and 7% increases, respectively, in pellet durability, water‐absorption index, and a*. Increasing the temperature from 100 to 140°C resulted in 17.0, 5.9, 35.4, 50.6, 28.8, 33.9, and 33.9% decreases, respectively, in unit density, pellet durability, sinking velocity, absolute pressure, specific mechanical energy, torque, and apparent viscosity, but a 49.1 and 16.9% increase, respectively, in dough temperature and water‐absorption index. Increasing the L/D ratio of the die nozzle resulted in an increase in bulk density, L*, a*, and torque, but a decrease in unit density, pellet durability, water‐absorption index, sinking velocity, b*, mass flow rate, dough temperature, and apparent viscosity. As demonstrated in this study, the selection of an appropriate die geometry, in addition to the selection of suitable temperature and moisture content levels, are critical for producing DDGS‐based extrudates with optimum properties.

Extrusion trials were conducted with varying levels of distillers dried grains with solubles (DDGS) along with soy flour, corn flour, fish meal, vitamin mix, mineral mix, and net protein content adjusted to 28% using a Wenger TX‐52 twin‐screw extruder. The properties of extrudates were studied in experiments conducted using a full‐factorial design with three levels of DDGS content, two levels of moisture content, and two levels of screw speed. Increasing the DDGS content from 20 to 60% resulted in a 36.7% decrease in the radial expansion, leading to a 159 and 61.4% increase in the unit density and bulk density of the extrudates, respectively. Increasing the DDGS content resulted in a significant increase in the water absorption index (WAI) but a significant decrease in the water solubility index (WSI) of the extrudates. Changing the screw speed and moisture content had no significant effect on the radial expansion ratio but resulted in a significant difference in the bulk density of the extrudates, which may be due to the occurrence of longitudinal expansion. Even though changing the moisture content and screw speed had no significant effect on the WSI of the extrudates, significant differences in the WAI of the extrudates were observed. The ingredient components in the blend and moisture content had an influence on the color changes of the extrudates, as did the biochemical changes occurring inside the barrel during processing. Overall, it was determined that DDGS could be included at a rate of up to 60% using twin‐screw extrusion, and that viable pelleted floating feeds can be produced.

Three isocaloric (3.5 kcal/g) ingredient blends containing 20, 30, and 40% distiller-dried grains with solubles (DDGS) along with 5% whey were prepared with a net protein content adjusted to 28% (wet basis [wb]). Other ingredients in the blends included soy flour, corn flour, fish meal, vitamin, and mineral mix. These blends were extruded in a single-screw extruder at 15, 20, and 25% (wb) moisture content and at 130 and 160 rpm screw speeds. Compared to previous research, the durability and unit density of the extrudates in this study were found to increase substantially by the addition of whey to the blends. Increasing the DDGS content from 20 to 40% resulted in a 5.8 and 16.8% increase in extrudate moisture content and redness, respectively, but produced a decrease of 11.2% in brightness and 3.6% in yellowness of the extrudates. Increasing the moisture content of the ingredient blends from 15 to 25% resulted in an increase of 16.1, 8.7, and 9.3% in moisture content, durability, and redness, respectively, but a decrease of 9.8 and 5.6%, respectively, in brightness and yellowness of the extrudates. Neither DDGS level nor screw speed significantly affected extrudate durability or unit density. In fact, changing the screw speed had no significant effect on many of the properties of the extrudates studied, except for moisture content, redness, and yellowness. As demonstrated in this study, ingredient moisture content and screw speed are critical considerations when producing extrudates with feed blends containing DDGS; further work is needed to optimize processing conditions and to produce floating feeds.

Three isocaloric (3.5 kcal/g) ingredient blends containing 20, 30, and 40% (wb) distillers dried grains with solubles (DDGS) along with soy flour, corn flour, fish meal, and mineral and vitamin mix, with 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 with 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.