USING DYNAMIC SHRINKAGE TESTS TO STUDY FISSURE PROPAGATION IN RICE KERNELS

Dynamic shrinkage behavior of rice kernels during drying was studied with a thermomechanical analyzer (TMA). Shrinkage kinetics data were obtained for brown rice kernels heated/dried in a TMA chamber. Seventeen rice kernels of long–grain variety Drew were tested for length change, and another seventeen kernels of the same variety were tested for thickness change. Each kernel was initially heated from room temperature to 59.7³C at a rate of 15³C/min and then maintained at 59.7³C to dry for 400 min. The shrinkage behavior of rice kernels could be described by an exponential decay relationship. Rice kernels did not shrink uniformly in thickness and length during the drying process but shrank a greater percentage in thickness than in length. Because of the non–uniform shrinkage, a tensile force along the direction of the longitudinal axis is speculated to exist during drying. This result may help explain why, with a small number of exceptions, fissures observed in rice kernels are perpendicular to the longitudinal axis of the kernel.