| This research study was done with a broad intention of enhancing the value of Distiller's Dried Grains with Solubles (DDGS) in aquaculture feeds for the production of floating and sinking feed using extrusion technology. The various ingredients used in the preparation of balanced blends included DDGS, soybean meal, starch sources (tapioca, corn, and potato), fish meal, whey, and vitamin and mineral mixes. The equipment used in the production of DDGS based extrudates were single screw extruder and a twin screw extruder. The feed parameters in the various experimental studies included: Starch sources (tapioca, corn, and potato), DDGS levels (17.5 to 60% db), feed moisture content (15 to 35% db), and net protein content (28 to 35% db). The extruder parameters included: Extruder screw speed (100 to 200 rpm) and extruder processing temperature (100 to 150°C). The effect of feed composition and extruder parameters on the physical properties of the extrudates, extruder processing parameters, and nutrient composition were investigated. The physical properties of the extrudates determined were moisture content (MC, % db), expansion ratio (ER, (-)), unit density (UD, kg/m3), bulk density (BD, kg/m 3), sinking velocity (SV, m/s), color (L*, a*, and b*), water absorption index (WAI, (-)), water solubility index (WSI, %), and pellet durability index (PDI, %). The extruder processing parameters investigated included moisture content at the die (% db), mass flow rate (MFR, g/min), apparent viscosity (Pa s), extruder torque (N-m), die pressure (MPa), and specific mechanical energy (SME, J/g). The proximate composition of DDGS based extrudates included crude protein (% db), neutral detergent fiber (% db), crude fat (% db), and ash (% db).;In the first study, the effect of various starch sources (tapioca, corn, and potato), DDGS levels, feed moisture content, processing temperature, and screw speed on the resulting extrudate properties were determined. Increasing the DDGS levels from 20 to 60% resulted in decreased ER, WAI, and PDI values for all the three starch extrudates. For all the three starch extrudates, a profound increase in ER and WAI values could be noticed for the change in the feed moisture content from 15 to 25%. Overall, tapioca starch extrudates were found to be more appropriate for the production of floating aquaculture feeds, where as corn starch extrudates were more durable.;As a second part of this research, the effect of DDGS levels and net protein content on the resulting DDGS based extrudates were analyzed. Increasing the DDGS levels from 20 to 40% decreased ER values for all the three starch extrudates but WAI and WSI values were found to decrease for corn and potato starch extrudates. On the other hand, a noticeable increase in PDI values were observed with an increase in DDGS and protein levels from 20 to 40% and 28 to 32%, respectively. In the overall analysis, it was noticed that tapioca starch incorporated in a 20% DDGS diet resulted in a floating feed more appropriate for tilapia.;The third part of the study was conducted with an intention of producing floating aquaculture feeds using a single screw extruder. Based on the previous experimental results, tapioca starch was used as the starch source in this study. Increasing the DDGS content from 20 to 30%, protein content from 30 to 32.5%, and temperature from 100 to 150°C resulted in decreased ER, WAI, and PDI values of the resulting DDGS based extrudates. Also, apparent viscosity, die pressure, and extruder torque decreased significantly with an increase in DDGS, protein levels, and processing temperature. As anticipated, mass flow rate increased with corresponding increase in extruder screw speed. |
