GLASS TRANSITION TEMPERATURE OF RICE KERNELS DETERMINED BY DYNAMIC MECHANICAL THERMAL ANALYSIS

A protocol was developed to measure the glass transition temperature (Tg) of brown rice kernels using dynamic mechanical thermal analysis (DMTA). In order to accommodate the sample requirements of the dynamic mechanical thermal analyzer and prevent moisture loss during experiments, kernels were first wrapped with a thin layer of parafilm and then a thin layer of aluminum foil. The wrapped kernels were then filed at both ends with fine sandpaper to produce 3 mm long rice cylinders with parallel ends. The dynamic mechanical properties of brown rice kernels were determined over a temperature range of -40°C to 120°C. During each DMTA test, the onset temperature of glass transition was measured as the Tg of a brown rice kernel, since moisture diffusion and other physical properties begin to change drastically above the onset temperature. No dramatic changes in both the storage modulus (E. ) and the loss modulus (E. ) of brown rice kernels were found around Tg, indicating that relaxation of the amorphous phase of the rice kernel was quite limited. However, E. / E. (tan.) showed a much better transition for brown rice kernels, and thus the E. / E. vs. temperature curves were used to determine Tg values of rice kernels. It was found that the Tg values of rice kernels decreased linearly with increases in moisture content (MC) within the tested range. The Tg of rice kernels was not affected by variety.