Dynamic Viscoelastic Properties of Rice Kernels Studied by Dynamic Mechanical Analyzer

Abstract

Dynamic viscoelastic properties of brown rice kernels were investigated using a dynamic mechanical analyzer (DMA). In order to meet the sample requirements for the DMA and prevent moisture loss of rice kernels during the DMA measurements, necessary precautions were taken. To prevent moisture loss of rice kernels during the DMA measurements at temperatures ranging from room temperature to 120 degrees centigrade, rice kernels were wrapped with a thin layer of sealing film. Then the wrapped rice kernels were additionally covered with an aluminum foil. Two ends of the wrapped brown rice kernels were cut with a razor blade; subsequently both ends of the cut rice kernels were filed using fine sandpaper to produce near cylindrical rice kernels with parallel ends. The storage modulus of the rice kernels decreased with increasing temperature and moisture content. The loss modulus and the tan delta (loss factor) of the rice kernels as a function of temperature showed clear peaks, which are associated with the glass transition of rice kernels. Two rice varieties had been investigated, and the results showed that the dynamic viscoelastic properties of these rice samples were not significantly different. The glass transition temperatures for the long-grain rice kernels with the moisture contents of 17.4, 13.8, and 10.9 wt.% were determined as 45, 58, and 66 degrees centigrade, respectively.