Net Isosteric Heats of Adsorption and Desorption for Different Forms of Hybrid Rice

Abstract

Hygroscopy of hybrid rice affects storage, handling, and processing. The thermodynamic relationship upon which the estimate of isosteric heat is based is the Clausius-Clayperon equation. The net isosteric heat of sorption was determined from the slope of the ln(rh) versus 1/T lines at a constant moisture content. Net isosteric heat of desorption was found higher than that for the adsorption within a moisture content range of 12–20% for all of the rice kernels. The net isosteric heats of desorption and adsorption were higher for hybrid rough rice kernels followed by brown rice and milled rice kernels, respectively. An empirical equation was fitted to describe the net isosteric heats of hybrid rice kernels as a function of moisture content and was found adequate to predict the net isosteric heats. The intercept K was also found to be a function of moisture content and the model predicted the K value well (r2 = 0.85 for adsorption and r2 = 0.92 for desorption). This set of two equations would be useful in the simulation of hybrid rice during storage.