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Abstract  

Classical thermogravimetry and its modification with Knudsen cells were employed to quantitatively investigate the osmo-dehydration of apple pulp samples. The data allowed realization of the complex mechanism of the process, which is not a mere solvent depletion, since it also implies sugar exchanges between the apple tissue and the hypertonic syrup used to dehydrate the fruit. The comparison between different hypertonic syrups, all at the same water activity, showed that maltose is more effective than either sucrose or a mixture of sugars that mimics the saccharide content of the apple. The conclusions are supported by a thermodynamic analysis of the aqueous solutions of these sugars at a concentration level as large as that of the hypertonic syrups used for the osmo-dehydration process.

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Journal of Thermal Analysis and Calorimetry
Authors: Pascal Clausen, Marco Signorelli, Andreas Schreiber, Eric Hughes, Christopher Plummer, Dimitrios Fessas, Alberto Schiraldi, and Jan-Anders Månson

Abstract  

Desorption isotherms for water, ethanol, ethyl acetate and toluene from a sodium smectite clay have been determined by both dynamic vapor sorption (DVS) measurements and Knudsen thermogravimetry (KTGA), at the exception of toluene that was measured only by the DVS method. The results obtained using these two methods were in satisfactory agreement, providing reliable insight into the desorption process, with certain lack of precision for ethyl acetate. The observed desorption behaviour suggests a liquid like phase at high volatile load, and a sorbed state in which molecules interact with the counter ions, at low volatile contents. However, the isotherms for water determined at various temperatures nearly superposed when plotted as a function of water activity, indicating the strength of the interactions in the clay–water system to remain of the same order of magnitude as that in bulk water, consistent with previous ab initio calculations.

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