Phase solubility studies of terpineol with β-cyclodextrins and stability of the freeze-dried inclusion complex

In present work, phase solubility analysis were conducted for studying the solubility of terpineol, a natural flavor compound with antifungal and disinfectant action, in 2-hydroxypropyl-β-cyclodextrin (HBCD) and in β-cyclodextrin (BCD) aqueous solutions and for calculating the thermodynamic parameters involved in the complex formation. Physical properties of the freeze-dried complexes were also evaluated as a function of water content and storage time. The solubility of terpineol increased linearly as the concentration of BCD or HBCD was increased, confirming the 1:1 stoichiometry of the complex. The negative value of the enthalpy and of the Gibbs energy demonstrated that the process is exothermic and spontaneous. Since complexation gives more ordered systems, the negative value obtained for the entropy change confirms the encapsulation of terpineol both in HBCD and BCD. The water adsorption data and glass transition values obtained revealed that complexation involves the displacement of water molecules from the cavity of the CDs by the guest compound that is being included.