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The effect of feed protein content levels and extrusion processing variables on extrudate properties of wheat flour and two wheat flour blends were assessed, Blends were made by mixing vital gluten containing 70% protein with the wheat flour (9% protein) to obtain 20 and 30% protein levels. Samples were extruded in a twin-screw extruder (APV Baker, Grand Rapids, MI) with full factorial combinations of die exit temperature of 120, 140, and 160℃; screw speed of 240, 320, and 400 rpm; and protein content levels of 9, 20, and 30%. Protein of raw feed material significantly affected expansion ratio, bulk density, water absorption index, and specific mechanical energy. Extruder exit die temperature also affected bulk density and specific mechanical energy significantly. Correlation data showed that screw speed and specific mechanical energy were positively correlated (r=0.95, p≤0.001), while die temperature was negatively correlated with bulk density (r=-0.38, p≤0.01). Protein content of feed negatively correlated with expansion ratio, water absorption index, and specific mechanical energy (SME) input, and positively with bulk density, while an inverse relationship existed between expansion ratio and bulk density. The protein content level of feed material was the only factor that significantly affected all extrusion dependent variable.
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