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A Review of Hygroscopic Equilibrium Studies Applied to Rice

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Transactions of the ASABE. 53(6): 1859-1872. (doi: 10.13031/2013.35795) @2010
Authors:   B.-M. Choi, S. B. Lanning, T. J. Siebenmorgen
Keywords:   Equilibrium moisture content, Equilibrium relative humidity, Hygroscopic equilibria, Isotherm, Rice

Equilibrium moisture content (EMC)/equilibrium relative humidity (ERH) studies pertaining to rice and rice products were reviewed. Methods of determining rice and rice component EMC/ERH data varied, using procedures involving static and dynamic equilibration methods, as well as direct gravimetric methods and indirect ERH-measurement methods. Methods for measuring rice and rice component moisture contents also varied. The Modified Henderson and Modified Chung-Pfost equations were most frequently recommended for predicting the sorption behavior of rice. Among rough rice components, for any given temperature and relative humidity, the EMC of milled and brown rice were consistently the greatest, generally followed by rough rice, bran, and hull. The hysteresis effect was apparent in rice. The magnitude of hysteresis decreased with repeated cycles of drying and rewetting and with increasing temperature. EMC/ERH relationships were affected by rice cultivar, but harvest location was not a significant factor. As such, in order to be most accurate, EMC/ERH equations for each rice cultivar need to be determined.

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