Abstract
ABSTRACT NON-WAXY corn gifts (30% amylose) and waxy corn grits (1% amylose) were extrusion cooked at 17.84, 20, 30, 40, and 42.16% moisture content, dry basis. Extruder barrel temperatures were 115, 120, 140, 160 and 164 C. Screw speeds between 95 and 166 rpm generated a varying shear environment in a C. W. Brabender extruder with a 1.9 cm barrel diameter, barrel length to diameter ratio of 20:1 and a 3:1 screw compression ratio. Statistical models for product expansion, bulk density, shear force, water holding capacity and percent gelatinization were developed as a function of product moisture content, barrel temperature, shear rate in the die and channel, residence time in the die and channel and shear strain. The selected models maximized the coefficient of determination while minimizing Mallows' Cp statistic which is a measure of the total squared error. In all models, feed moisture content and barrel temperature were found to be highly significant.
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