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CHARACTERIZATION OF VISCOELASTIC PROPERTIES OF INDIVIDUAL RICE GRAIN BY MEASURING MECHANICAL IMPEDANCE

The viscoelastic properties of individual rice grains were measured by using a novel oscillatory squeezing instrument. Specifically, rice grains at different moisture contents and cooking durations were chosen as the model grain, and their viscoelastic characteristics, namely viscous modulus and elastic modulus, were determined. During the measurement, the grains were squeezed between a rigid bottom plate and a top round element oscillating at random frequencies in the range of 10-30,000 rad/s. The mechanical impedance of the rice samples, defined as the ratio between the force applied to the samples and the oscillation velocity, was obtained and used to calculate viscoelastic parameters. Measurements with the grains having moisture content between 12.8 and 29.1% indicated that both viscous and elastic moduli of the samples decreased significantly with increasing moisture content. The measured mechanical impedances of the samples showed that changes in viscoelastic properties for various cooking periods can be also monitored using the proposed oscillatory squeezing method.