Influence of Particle Size on the Twin-Screw Extrusion of Corn Meal

Effects of particle size (50–1,622 µm), screw speed (200–400 rpm), and feed moisture content (19–22%) on twin-screw extrusion of corn meal were investigated using a full-factorial design. Torque, specific mechanical energy, and product temperature generally showed no change within the commonly used particle-size range (100–1,000 µm), but each value dropped significantly as the particle size increased >1,000 µm. Die pressure was influenced by the three-way interaction of particle size, screw speed, and feed moisture content. The highest moisture level (22%), largest particle size (1,622 µm), and two lowest screw speeds (200 and 300 rpm) were the only conditions where the starch was <97.5% of transformation (gelatinization). Consequently, these two conditions also showed the least expansion and hardest product.