The temperature dependence of isosteric heat of sorption of some cereal grains

Abstract

An equation predicting the temperature dependence of the isosteric heat of sorption was calculated using the Othmer method. This equation was applied to water vapour pressure isotherms of cereal grains (sorghum, wheat and rough rice) at different temperatures to calculate the isosteric heat and its dependence on moisture content and temperature. The results show a slight decrease of the isosteric heat with increasing temperature. For rough rice grain, the desorption heats calculated by the proposed method at two temperatures were compared with those obtained by the Clausius-Clapeyron method.Vapour pressures were calculated as P, = a,Pt using Pe at different 40,50,60,70 temperatures from Wexler (1976).

Moisture desorption isotherms of rough rice at high temperatures

“…This procedure has been widely used to determine the isosteric heat of adsorption or desorption for many cereals (Aguerre, Suárez, & Viollaz, 1988;Muthu & Chattopadhyay, 1993;Putranon, Bowrey, & Fowler, 1980;Tolaba et al, 2004). The values of water activity were obtained using the equation that better fits experimental moisture sorption data for the temperature range studied.…”

Moisture sorption isotherms and isosteric heat of sorption of coffee in different processing levels

“…Thermodynamic principles are applied in sorption isotherm data to obtain more information about energy requirement of dehydration, properties of water, food microstructure, physical phenomena on food surfaces and sorption kinetic parameters. One method widely used for calculating isosteric heat of sorption is based on the Clausius–Clapeyron equation, which assumes temperature‐independent heat of sorption and allows easy calculation of isosteric heat from sorption isotherms (Aguerre et al. , 1988).…”

Higroscopic properties of castor seeds (Ricinus Comunis L.)

“…An alternative method for calculating isosteric heats developed by Othmer (Perry and Chilton, 1991) assumes that the heats of both sorption and condensation have the same temperature dependence. This assumption is less restrictive than the Clapeyron method, in which both heats are considered to be constant (Aguerre et al, 1988).…”