The viscoelastic properties of extruded cornstarch were measured as a function of process conditions. The extruded cornstarch samples were conditioned in the moisture range of 12.9–31.2% (dry basis). Dynamic and creep behavior of the extrudate were evaluated using a dynamic mechanical analyzer. The storage (G′) and loss moduli (G″) were determined in the temperature range of 30–100C and oscillation frequency range of 0.1–51 Hz. The G′ and G″ values showed an increasing trend with a decrease in temperature and moisture content and an increase in frequency. This implied an increase in solid-like behavior when the temperature and moisture content were reduced or the frequency was increased. Rheological parameters based on creep behavior were assessed at 30, 60 and 85C. Creep data, fitted using Burger's model, were highly dependent on both moisture content and temperature.
The viscoelastic properties obtained in this experimental research can be used for solving the non-Fickian fluid transport model for studying the expansion of starch during extrusion. The viscoelastic properties also provide an indication about the textural characteristics of starch as a function of extrusion conditions.