Optimization of extruder cooking conditions for the manufacture of fish feeds using response surface methodology
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A composite blend consisting of sunflower cake, maize germ, wheat bran, fresh water shrimps and cassava flour was extruded using a single-screw extruder to produce expanded fish feed pellets. The effects of temperature (80-120 degrees C), die diameter (2-4mm), and feed pre-conditioning time (50-150 s; steam 400 kPa) on properties of the pellets (expansion ratio, bulk density, floatability, durability, water absorption, water solubility, water stability, and in-vitro protein digestibility) were investigated using response surface methodology. Regression equations describing the effect of each variable on the product responses were obtained. The pellets extruded using a factor combination of 120 degrees C extruder barrel temperature, 2 mm die diameter, and 100s of feed pre-conditioning time gave most desirable pellet floatability (100%), durability index (99%), expansion ratio (2.64), water absorption index (4.12), water solubility index (9.31), water stability (87%), bulk density (479 g/L), and in vitro protein digestibility (69.97%) with a composite desirability of 0.88.
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