USING DYNAMIC SHRINKAGE TESTS TO STUDY FISSURE PROPAGATION IN RICE KERNELS

Abstract

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 oflonggrain variety Drew were tested for length change, and another seventeen kernels of the same variety were tested forthickness change. Each kernel was initially heated from room temperature to 59.7C at a rate of 15C/min and thenmaintained at 59.7C to dry for 400 min. The shrinkage behavior of rice kernels could be described by an exponential decayrelationship. Rice kernels did not shrink uniformly in thickness and length during the drying process but shrank a greaterpercentage in thickness than in length. Because of the nonuniform shrinkage, a tensile force along the direction of thelongitudinal 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.