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Water Absorption Characteristics and Volume Changes of Milled and Brown Rice During Soaking

¹Department of Food Science and Technology, Faculty of Bioindustry, Tokyo University of Agriculture, 196 Yasaka, Abashiri-shi, Hokkaido, 099-2493, Japan. ²Corresponding author. Phone: +81-152-48-3852. Fax: +81-152-48-2940. E-mail: y-murama@bioindustry.nodai.ac.jp ³Graduate School of Science and Technology, Chiba University, 648 Matsudo, Matsudo-shi, Chiba-ken, 271-8510 Japan. ⁴Department of Bioproduction and Environment Engineering, Faculty of Regional Environment Science, Tokyo University of Agriculture, 1-1-1 Sakuraoka, Setagaya-ku, Tokyo, 156-8502 Japan.

The water absorption characteristics and volume changes of rice with various degrees of milling during soaking were measured at five temperatures (5–40°C). The measured data were fitted to the exact solution for the infinite plane sheet diffusion model, which is an exact solution for the diffusion equation. The measured results agreed well with the model. The effects of temperature and the degree of milling on the water absorption rate constant were investigated. Volume changes of samples were determined by measuring particle density and bulk density. An empirical equation relating the moisture content of the sample during soaking and at temperatures of 10–50°C to specific volume was derived. In addition, bulk density was related to the quadratic function of the moisture content of the sample during soaking.