INTRA–KERNEL MOISTURE RESPONSES OF RICE TO DRYING AND TEMPERING TREATMENTS BY FINITE ELEMENT SIMULATION

Abstract

Moisture content patterns inside rice kernels are important in understanding rice fissure formation, especiallywhen glass transition effects are considered. Unsteady and nonlinear partial differential equations were employed todescribe twodimensional temperature and moisture distributions within a single rice kernel during drying and temperingprocesses. Moisture content gradients (MCGs) inside the kernel were examined. Results showed that the maximum MCG(MMCG) appeared in the direction of the short axis. During the tempering process, moisture content on the kernel surfacehad a much faster and greater change than that at the kernel center. The intrakernel MCG decreased considerably duringthe first 40 min of tempering, after which it decreased slowly to approach zero. A duration of about 40 min of tempering at60C helped eliminate about 90% of the MCGs created inside the rice kernel during drying, and this simulation resultcorrelated favorably with the published tempering data in the literature. The findings from this study provided usefulinformation for determining optimal drying and tempering conditions of rice to enhance its milling quality.