Effect of different extrusion conditions and pellet size on the physical properties of extruded fish feeds

This work presents useful information on how different temperature profiles during the extrusion process affect the physical quality properties of the extrudates. In this study, feed mixtures were extruded using a twin-screw extruder; the barrel temperature profile was set at 110 °C for cooking extrusion process, and no additional heat for cold process. Four extruded diets were designed: D2LT and D4LT for 2 mm and 4 mm diet produced with cold process, respectively, and D2HT and D4HT for 2 mm and 4 mm diet produced with cooking extrusion. Pellet durability index (PDI), expansion ratio (ER), sinking velocity (SV), water stability (WS) and water absorption index (WAI) were affected with the temperature condition. The pellets produced with cooking extrusion had a higher PDI, SV, WAI and WS compared to cold process (p < 0.0001). There was no significant difference in terms of ER between the extruded diet processed with different temperature at the same particle size. Reducing particle size from 4 mm to 2 mm significantly affect the PDI, WAI. SV, WAI and WS in cooking extrusion diet. In cold process, the significant differences were found in PDI, ER, and WS, but no significant differences in SV and WAI.