Effects of Selected Process Parameters on Expansion and Mechanical Properties of Wheat Flour and Whole Cornmeal Extrudates

Mechanical properties of cereal extrudates are recognized by consumers as quality criteria. These properties are affected by process variables. The effect of process variables, such as water injection rate, barrel temperature, and screw speed on the expansion and selected mechanical properties of wheat flour and whole cornmeal extrudates was determined. A laboratory-scale twin-screw extruder with an L/D ratio of 25.0 was used. The cross-sectional expansion, the specific length, and the elastic moduli and breaking strength in bending and compression were measured. Water injection rate and barrel temperature significantly affected the cross-sectional expansion index (SEI) (P < 0.01), specific length (P < 0.01), elastic modulus in compression (P < 0.05), and breaking strength in bending (Ps 0.05). The SEI was increased with a decrease in water injection rate and/or an increase in barrel temperature. The elastic modulus and breaking strength in bending decreased with the decrease in water injection rate. The SME input, which was dependent on the process variables tested, also influenced the expansion and mechanical properties of extrudates. The higher the SME input was, the lower the elastic moduli and breaking strength were. This result confirmed that the texture of extruded product was controlled by changing the SME input.