Heat of sorption and free energy change of freeze-dried pineapple pulp

Abstract

Two thermodynamic properties, the heat of sorption (Qs) and the Gibbs free energy change (∆G) were evaluated at several temperatures (5, 25, 30, 35 and 55°C) on freeze-dried pineapple pulp. It was found that 1) the heat of sorption follows the Clauslus-Clapeyron relationship; 2) the shape of the heat of sorption vs. the equilibrium moisture content curve was sigmoid; 3) the heat of sorption from adsorption data gave higher values than those from desorption data; and 4) the free energy change (∆G) is linearly related to the equilibrium moisture content. These two parameters are very important in dealing with food stability because it is possible to predict the water activity at any given temperature of either of these values is known.