34 CEREAL CHEMISTRY Effect of Single-Screw Extruder Die Temperature, Amount of Distillers’ Dried Grains With Solubles (DDGS), and Initial Moisture Content on Extrudates 1 C. Y. Shukla, 2 K. Muthukumarappan, 2,3 and J. L. Julson 2 ABSTRACT Cereal Chem. 82(1):34–37 Corn distillers’ dried grains with solubles (DDGS) was extruded with corn meal in a pilot plant single-screw extruder at different extruder die temperatures (100, 120, and 150°C), levels of DDGS (0, 10, 20, and 30%) and initial moisture contents (11, 15, and 20% wb). In general, there was a decrease in water absorption index (WAI), water solubility index (WSI), radial expansion, and L* value with an increase in DDGS level, whereas a* value and bulk density increased. Increase in extruder die temperature resulted in an increase in WSI and WAI but a decrease in L* and bulk density. Peak load was highest at 30% DDGS as compared with 0, 10, and 20% DDGS extrudates. Die temperature of 120°C and initial moisture content of 20% resulted in least peak load. The a* value remained unaffected by changes in extruder die temperature. Radial expansion was highest at extruder die temperature of 120°C. Maximum WAI, WSI, radial expansion, and L* value were obtained at 15% initial moisture content. An increase in initial moisture content, in general, decreased L* value and bulk density but increased a* value of extrudates. Corn distillers’ dried grains (DDG) and distillers’ dried grains with solubles (DDGS) are coproducts of the ethanol industry. The starch fraction of corn is fermented using selected yeasts and enzymes to produce ethanol. The residues remaining after ethanol extraction are dried to produce DDGS, which is high in fiber, fat, and protein. Extruders have established their position in the food industry and have become irreplaceable. The variety of extruded products ranges from pasta, ready-to-eat breakfast cereal, and snack food to confectionery and pet foods (Harper 1979; Harper and Jensen 1985; Frame 1994). Carbohydrate-based snack foods are usually extruded. Crispness, a typical quality attribute of all snack foods, is strongly related to the expansion that, in turn, is dictated by various extrusion parameters (Chinnaswamy and Hanna 1988). Extrusion cooking conditions and their effect on product qualities have been studied and modeled (Gomez and Aguilera 1984; Owusu-Ansah et al 1984; Bhattacharya and Hanna 1987), and it is known that extrusion variables including ingredient factors and process factors affect extrudate nutritional and functional qualities (Harris et al 1988). Several groups (Saterlee et al 1976; Breen et al 1977; Walker 1980; Anderson et al 1981) evaluated either corn or wheat DDG in extruded snacks and reported that >20% DDG caused a loss in radial expansion. Extruder barrel temperature affected the expan- sion of corn starch (Mercier and Feillet 1975). The interaction of temperature and screw speed effects on L* was reported by Apruzzese et al (2000). They reported that the influence of tem- perature on the viscosity of melt may cause a great degree of browning at 150°C barrel temperature than at 170°C. Lower moisture contents favored the expansion of materials such as corn grits, corn starch (Mercier and Feillet 1975; Gomez and Aguilera 1984), and corn germ flour (Peri et al 1983). Empirical studies have shown that initial moisture content and extrusion temperature are the most important variables influencing expansion in any par- ticular system (Lawton et al 1972; Merceir and Feillet 1975; Park 1976; Hauck 1981; Holay and Harper 1982). No study, however, has appeared that reports the effect of extruder die temperature at different levels of DDGS and initial moisture content on func- tional properties of extrudates. Therefore, the objective of this study was to evaluate the effect of extruder die temperature (100, 120, and 150°C) on functional properties of extrudates like hydration properties (WSI and WAI), color properties (L* and a*), radial expansion, peak load, and bulk density at varying DDGS levels (0, 10, 20, and 30%) and initial moisture content (11, 15, and 20% wb). MATERIALS AND METHODS Ingredients and Pretreatment Distillers’ dried grains with solubles (DDGS) was obtained from Dakota Ethanol, LLC (Wentworth, SD) and corn meal was ob- tained from ADM Co. (Milwaukee, WI). Experimental design (3 × 3 × 4) consisted of three levels of die temperature (100, 150, and 120°C), three levels of initial moisture content (11, 15, and 20% wb), and four levels of DDGS (0, 10, 20, and 30%). DDGS and corn meal were mixed in required proportions. The formula- tions were blended (20 qt. capacity, hub size #12, model A200 with three gears for planetary action, Hobart, Troy, OH) for 15 min. Initial moisture was adjusted to the desired level (Table I) and the formulation was further blended for 5 min. The formulation was stored in an airtight container overnight to attain moisture equili- brium. Three extrusion replicates were conducted. Extrusion A single-screw extruder (C. W. Brabender Plasticorder Extruder model PL-2000) with a barrel length-to-diameter ratio of 20:1 and compression ratio of 3:1 was used for all experiments. The PL- 2000 had variable screw speed from 0 to 210 and three heating 1 Request to publish this research article approved by Agricultural Experiment Station, South Dakota State University. Journal number 3405, dated 01/02/2004. 2 Research associate, associate professor, and associate professor, respectively, Agri- cultural and Biosystems Engineering, South Dakota State University, Brookings, SD 57007. 3 Corresponding author. Phone: 605-688-5661. Fax: 605-688-6764. E-mail: muthukum@sdstate.edu DOI: 10.1094/CC-82-0034 © 2005 American Association of Cereal Chemists, Inc. TABLE I Experimental Design Formulation Die Temperatures (°C) Initial MC (%, wb) 0% DDGS 100% Corn meal 100 11 120 15 150 20 10% DDGS 90% Corn meal 100 11 120 15 150 20 20% DDGS 80% Corn meal 100 11 120 15 150 20 30% DDGS 70% Corn meal 100 11 120 15 150 20