Sorption isotherm and calorimetric behavior of amorphous/crystalline raffinose-water systems

The water adsorption and desorption isotherms at 21 degrees C of initially amorphous raffinose over a range of relative humidity of 11% to 97% have been determined. Upon adsorption, the isotherm exhibited a "quasi" plateau, and the moisture content at this plateau was found to be very close to the amount required to form the crystalline raffinose pentahydrate (R.5 H2O). Crystallization of raffinose (R.5 H2O) during water adsorption at 52% and 58% RH was indicated by differential scanning calorimetry (DSC); both thermograms showed an endothermal peak of melting corresponding to R.5H(2)O. The results of the crystallization kinetics at 52% and 58% RH indicated that the time to assess the stable physical state in a sugar system for a given external condition has to be properly defined and depends on the (T-T-g) value.