Moisture Equilibrium in Apples at Several Temperatures: Experimental Data and Theoretical Considerations

ABSTRACT Moisture equilibrium data for desorption of water from apples was determined at 20°, 30°, 40°, 50° and 60°C. The rehydration 40°C isotherm was also found. The experimental procedure was a gravimetric dynamic method. Sorptive capacity decreases as temperature increases. Rehydration of the dried material results in hysteresis. The data are interpreted in thermodynamic terms. Specific surface and monolayer concentrations are also found. Pore size distribution studies show that the most frequent pore radius at 20°C and 40°C are, respectively, 26 Å and 22 Å. Hysteresis data are compared with what would be expected from the cellulose wall, indicating that solubility and other effects increase sharply the sorptive capacity of the fruit. A comparison of desorption and adsorption characteristics shows that dehydration results in serious damage of the fruit structure.