Moisture Diffusivity in Rice Components During Absorption and Desorption

Abstract Moisture diffusivity values of different rice kernel components, namely endosperm, bran and husk, are required to solve mathematical models describing absorption and desorption processes. In addition to the rice variety and temperature, the moisture diffusivity also depends on its instantaneous moisture content or water activity (aw) and whether rice is absorbing or desorbing moisture. This research was undertaken to determine moisture diffusivity values of rough rice components in different aw ranges during absorption and desorption. Experiments were performed to measure sorption rates of different rice forms, including white rice, brown rice, and rough rice kernels. Mathematical models were developed to predict their moisture distribution during moisture sorption processes. These models were solved by finite element method using Comsol Multiphysics® simulation program. Moisture diffusivity values of different rice components were calculated and found to be different during absorption and desorption. Diffusivity of rice endosperm was higher during desorption than absorption at aw higher than 0.20 and increased with an increase in aw in 0.20–0.80 aw range. Diffusivity of bran remained almost the same with aw while diffusivity of husk decreased with an increase in aw. Results obtained in this research demonstrated that the moisture diffusivity of different rice components varies significantly with the change in water activity or moisture and should be accounted in the mathematical models. Keywords: Mathematical modellingMoisture transportRiceSorption ACKNOWLEDGMENTS We thank the California Rice Research Board for providing partial financial support for this research.