Thymol and cinnamaldehyde formed inclusion complexes with beta-cyclodextrin (beta-CD) upon mixing the components in aqueous media and subsequent freeze-drying, as confirmed by differential scanning calorimetry. The samples were stored at constant relative humidities (RH) from 22% to 97%, at 25 degrees C. The release of encapsulated compounds was determined following the melting enthalpy of each guest. Water sorption isotherms for beta-CD and the complexes showed constant and low water sorption at RH <80%, then the uptake of water increased abruptly. The amount of sorbed water at each RH was smaller for the complexes than for beta-CD. The guest molecules displaced water molecules from inside the cavity of beta-CD. No thymol or cinnamaldehyde release was detected at RH <84%, and it increased abruptly from 84% RH, coincidentally with the abrupt increase of sorbed water. Water sorption significantly affects beta-CD complexes stability, which is thus governed by the shape of the water sorption isotherm. (C) 2010 Elsevier Ltd. All rights reserved.