Moisture adsorption isotherms of rough rice

Moisture adsorption isotherms of medium-grain rough rice were determined using a constant environment chamber for various combinations of air relative humidity (56-89.3%) and temperature (17.8-45 degrees C). A thin-layer technique was employed to achieve uniform re-wetting. An oven as a self contained air conditioning unit, recently developed in Japan, was used for this experiment. Four commonly cited EMC/ERH equations, i.e. modified Henderson, modified Chung-Pfost, modified Oswin and modified Halsey equations were compared for their ability to fit the experimental data. The comparison shows that the modified Chung-Pfost equation is the best equation for describing the EMC/ERH adsorption isotherms of rough rice. Temperature dependent functions of the modified Henderson, modified Chung-Pfost and modified Oswin equations were empirically modified to fit with the multiple linear regression techniques. The adsorption EMC data obtained in this work agree with the previous data. These fitted equations are based on a wide range of temperatures and relative humidities and therefore provide a useful basis for future work on drying and storage of rough rice. (C) 2000 Elsevier Science Ltd. All rights reserved.