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 (a_w) and whether rice is absorbing or desorbing moisture. This research was undertaken to determine moisture diffusivity values of rough rice components in different a_w 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 a_w higher than 0.20 and increased with an increase in a_w in 0.20–0.80 a_w range. Diffusivity of bran remained almost the same with a_w while diffusivity of husk decreased with an increase in a_w. 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 modelling
• Moisture transport
• Rice
• Sorption

ACKNOWLEDGMENTS

We thank the California Rice Research Board for providing partial financial support for this research.