Establishment of Optimized Manufacturing Conditions for Cooked Rice -Part II- Moisture Transfer Kinetics of Cooked Rice when Drying and Soaking in Water

Abstract

The thin-layer drying characteristics of cooked milled rice during hot air drying were measured at four temperatures (30, 40, 50, and 60 °C) and at a relative humidity of 40%. The hot air-drying process of the sample was composed of the first falling rate, and the exponential model was applied to predict the changes in moisture content of the sample at each temperature. The drying rate constant of the sample increased as temperature increased and was expressed as an Arrhenius-type equation. The water absorption characteristics of dried cooked milled rice when soaking in water were examined at four temperatures (70, 80, 90, and 98 °C). The ratios of the changes in moisture content from 8 to 150% (d.b.) were converted from the data of changes in moisture content. The first-order reaction rate equation could be applied to explain the water absorption process of samples. The water absorption rate constant had a tendency to increase with increasing soaking temperature and was expressed as a function of soaking temperature by an Arrhenius-type equation.