A new method to determine viscoelastic properties of corn grits during cooking and drying

The working principles and the theoretical background of a new method to measure the viscoelastic properties of grains during cooking and drying processes are presented. Specifically, corn grits at different processing stages of cooking and drying were chosen as the model grain and their viscoelastic characteristics, namely elastic stiffness and viscous damping, were determined. During the measurements grits were squeezed between a rigid bottom plate and a top round element oscillating at random frequencies in a range 10–10,000 rad/s. A frequency response of the mechanical impedance of the samples, which is defined as the ratio between the force applied to the samples and the oscillation velocity, was obtained. Corn grits were measured in their raw state, after cooking in a pressure cooker for different times (2, 7, 15, 30, and 60 min), and at different times of drying (30, 60, and 120 min) at 65 °C. The measured mechanical impedances of the samples showed that rheological changes upon processing can be monitored by the newly developed method. Non-destructive and quick measurements, data covering a wide range of frequencies, and the adaptability of the method to be used with available instruments used in texture measurement such as texture analyzers are some of the important advantages that the new method provides to the area of cereal processing.