MOISTURE DIFFUSIVITY OF LONG-GRAIN RICE COMPONENTS

Moisture adsorption of long-grain rice was modeled using the finite element method. The rough rice kernel was considered a prolate spheroid comprised of three homogeneous components: endosperm, bran, and hull. Adsorption tests were conducted on white, brown, and rough rice of the 'Newbonnet' and 'Lemont' varieties at temperatures ranging from 12-degrees-C to 50-degrees-C. Diffusivity values were determined for each rice component and each rice form (i.e., rough, brown, and white rice) using a finite element program with an optimization subroutine. White rice had the highest adsorption rate and rough rice the lowest. Endosperm had considerably higher diffusivity values than the bran and hull. The diffusivities of 'Lemont' rice components were found to be more temperature-dependent than those of 'Newbonnet'. The diffusivity temperature-dependency for each rice component and form was described by an Arrhenius-type function.