PUBLISHING MEDWELL Journal of Aquaculture Feed Science and Nutrition 1 (1): 6-21, 2009 ISSN: 2070-1667 © Medwell Journals, 2009 Corresponding Author: Kurt A. Rosentrater, USDA-ARS, North Central Agricultural Research Laboratory, 2923 Medary Ave. Brookings, SD 57006, USA 6 Effects of Ingredients and Extrusion Parameters on Aquafeeds Containing DDGS and Tapioca Starch S. Kannadhason, K. Muthukumarappan and Kurt A. Rosentrater 1 1 2 Department of Agricultural and Biosystems Engineering, South Dakota State University, 1 Brookings, SD 57007, USA USDA-ARS North Central Agricultural Research Laboratory, 2 2923 Medary Ave., Brookings, SD 57006, USA Abstract: Isocaloric (3.05 kcal gG) ingredient blends were factorially formulated using three levels each of 1 DDGS (20, 25 and 30% db), protein (30, 32.5 and 35% db) and feed moisture content (25, 35 and 45% db), along with appropriate quantities of tapioca starch, soybean meal, fish meal, whey, vitamin and mineral mix to produce a balanced diet for tilapia feed. The ingredient blends were extruded using a laboratory-scale single screw extruder with varying screw speeds (100, 150 and 200 rpm) and extruder barrel temperatures (100, 125 and 150°C). The resulting extrudates were subjected to extensive analyses of physical properties, which included moisture content, unit density, bulk density, expansion ratio, sinking velocity, water absorption, water solubility, color (L*, a* and b*) and pellet durability indices. Several extruder parameters, including moisture content at the die, apparent viscosity, specific mechanical energy, mass flow rate, net torque and die pressure were measured to quantify the extruder behavior during processing. All process settings used produced viable extrudates, but some were of better quality than others. For example, increasing the DDGS levels from 20-30% db, protein content from 30-35% db, feed moisture content from 25-45% db and processing temperature from 100-150°C significantly decreased the PDI values by 7.50, 16.2, 17.2 and 16.6%, respectively. Increasing the feed moisture content from 25-45% db resulted in a substantial increase in SME values by 256.2%. On the other hand, increasing the screw speed from 100-200 rpm significantly decreased the SME values by 33.7%. This study highlights the importance of experimentally determining the effects of feed ingredients and process variables when developing aquafeeds from novel materials. Key words: Tapioca starch, Distillers Dried Grains with Solubles (DDGS), extrusion, extruder parameters, physical properties INTRODUCTION Aquaculture is a rapidly growing sector of agriculture Starch is a biopolymer which is comprised of two prepared feed (Riaz, 1997). Two of the major challenges for types of macromolecules, namely amylose and profitable fish feed production include feed formulation amylopectin (Brouillet-Fourmann et al., 2003). It is well and processing (Kazamzadeh, 1989). Aquafeed known that a key modification during processing is formulation plays a crucial role in product buoyancy, micro molecular degradation of starch, which affects both especially given the challenge of manufacturing high amylose and amylopectin components (Colonna and quality protein, high fat rations with acceptable pellet Mercier, 1983; Davidson et al., 1984). Starch, an important durability and immersion stability (Rokey and Plattner, carbohydrate constituent, is best characterized in terms of 2004). The major characteristics which affect the quality of loss of crystallinity and gelatinization during extrusion fish feed include color, pellet size, shape, bulk density, (Colonna et al., 1983; Gomez and Aguilera, 1984; water absorption and solubility, hardness or softness, Chinnaswamy et al., 1989). Starch plays a vital role in the resiliency, buoyancy and chewiness (Kazamzadeh, 1989). production of floating or sinking feeds, because it acts as Currently, the largest cost component in aquaculture a binder and impacts product expansion. The minimum production is feed, which constitutes between 30 and starch content needed for floating and sinking feed are 60% of the total operational costs of the farm; protein is generally 18-22 and 9-11%, respectively (Riaz, 1997). often the most expensive nutritional factor. Therefore, and is one of the most reliable growth markets for