Establishment of Optimized Manufacturing Conditions for Cooked Rice -Part I- Equilibrium Moisture Content and Latent Heat of Vaporization of Cooked Rice

Abstract

The equilibrium moisture contents of cooked milled rice in the desorption process were measured at several temperatures (20-60°C) and relative humidity levels (10-86%) by a static method. The equilibrium moisture content of the sample increased with increasing equilibrium relative humidity at a constant temperature and increased with a decrease in temperature at any given equilibrium relative humidity. The Chen-Clayton equation, which is a sorption isotherm, was used to express the relationship between the equilibrium moisture content of the sample, equilibrium relative humidity, and absolute temperature. The latent heat of vaporization of water for the cooked rice was calculated by using the Chen-Clayton equation and thermodynamic theory (Clapeyron equation). At a moisture content of 15-30% (d.b.) (d.b.: the amount of water per unit mass of dry matter present in the material), the latent heat of vaporization of the sample decreased almost exponentially with an increase in moisture content. For samples at a moisture content above 50% (d.b.), the values of latent heat of vaporization sufficiently approached that of free water.