Effect of Extrusion Operating Parameters on AIr Bubble Entrapment

The effect of different extrusion operating parameters on air bubble entrapment during twin‐screw extrusion of amylopectin half‐products was studied. A ZSK‐30 twin‐screw corotating extruder with a slit die attached to the discharge end of the extruder to cool the extrudate to prevent water vapor puffing was used. The extrusion parameters investigated were screw speed (150, 300 and 500 rpm), mass flow rate (1.67 and 3.33 g s−1), native versus pregelatinized amylopectin, screw configuration (with or without kneading blocks), and moisture content (32 and 35%, w.b.). The parameters that exerted the greatest effect on air bubble entrapment during twin‐screw extrusion are the type of amylopectin used, mass flow rate and screw speed. On the other hand, in the ranges studied screw configuration and moisture content did not show any significant effect on air bubble entrapment. Explanations for these results are interpreted with the aid of the barrel fill length mechanism proposed by Cisneros and Kokini (2001).