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 be en determined. Upon adsorption, the isotherm exhibited a "quasi" plateau, a nd the moisture content at this plateau was found to be very close to the a mount required to form the crystalline raffinose pentahydrate (R.5 H2O). Cr ystallization of raffinose (R.5 H2O) during water adsorption at 52% and 58% RH was indicated by differential scanning calorimetry (DSC); both thermogr ams showed an endothermal peak of melting corresponding to R.5H(2)O. The re sults 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 exte rnal condition has to be properly defined and depends on the (T-T-g) value.