Changes in functionality of soy-based extrudates during single-screw extrusion processing

The effects of defatted soy flour content, feed moisture, screw speed and temperature on the functionality of soy-based extrudates were studied. Defatted soy flour and corn flour were mixed with ratios from 10% up to 30% of soy flour. The moisture contents of the blends (wet basis) have three levels: 15%, 18% and 21%. The barrel temperatures and screw speeds of the single screw extruder were controlled from 155 to 185degreesC and 180 to 220 rpm range, respectively. Shear force, color of the extrudates, expansion ratio, bulk density and water absorption were measured. Higher soybean flour content significantly increased shear force, bulk density and Hunter a* values and significantly decreased expansion ratio and Hunter L* values. High feed moisture significantly increased bulk density and Hunter L* values while significantly decreasing shear force and Hunter a* values. High process temperature significantly increased shear force and Hunter a* values and decreased bulk density. Increasing screw speed resulted in significantly increased bulk density. Understanding the relationship between extrusion parameters and physicochemical properties of the extrudates provides a basis for effective product development.