2.3 Extrusion and expansion processes
Extrusion experiments were performed using a laboratory
single extruder (model GNF 1014/2, Brabender, Inc., Duisburg,
Germany) with three heating zones, a 380 mm long and
19 mm diameter extruder barrel, and a compression ratio
of 2:1. A rectangular die with internal measurements of
1.5 × 20 × 100 mm long was used. The barrel temperature in
the cooking zone (intermediate zone) was varied according
to the experimental design, ranging from 75 to 140 °C. The
temperature in the initial zone (feed zone) and zone die (zone
output) was maintained constant at 60 and 90 °C, respectively.
The feed moisture varied from 16 to 30%. The feed rate was
maintained constant at 47.3 ± 2.36 g and a screw speed of
103 rpm. These variables were fixed based on preliminary
experiments. Non-expanded pellets were obtained from the
extrusion process.
The extruded pellets were dehydrated before expansion at
9.5-10.5% moisture (d.b.) (50 °C for 18 hours), cut into 2 cm
pieces, and expanded by microwave heating for 25 seconds in
a conventional microwave oven (Samsung, model MW843WA,
1200 W and 60 Hz). These conditions were established on the
basis of preliminary studies