Aquafeed Extrudate Flow Rate and Pellet Characteristics from Low-Cost Single-Screw Extruder

Abstract

Extrudate flow rate and effects of extrusion variables on extrudate properties were studied in a laboratory (small-scale) singlescrew, cooking extruder by extruding a marine shrimp feed mix. Response surface design was followed to examine the effect of screw speed (20-140 rev/min), L/D ratio (8-16), barrel temperature (60-100°C) and moisture content of feed mix (20-60%). All the variables were highly significant having positive linear relationship (r² = 0.99) with the experimental flow rate Q_Exp. Q_Theo calculation from the simplified flow model, however, over-predicted Q_Exp within 9 to 89%. Prediction improved with increased L/D ratio, screw speed, mosture content, and barrel temperature. The combined effects on water stability, expansion ratio and true density of extrudate showed that L/D 12-14 and moisture content 30-35% were optimum for the three properties, and 92-94 rev/min was the optimum speed for water stability and true density. Barrel temperature showed optimum values within 68-94°C. The most desirable values of the properties were 90.3% water stability, 0.99 expansion ratio, and 1347.9 kg/m³ true density.

Key Words:

• Extrusion
• aquafeed processing
• volumetric flow rate
• pellet characteristics