The interactions of 12 essential oils with α- and β-cyclodextrins (α-CyD, β-CyD) were investigated in aqueous solution and in solid phase by solubility method, powder X-ray diffractometry, and thermal analyses (DTA, TG). Referring to the Bs type phase solubility diagrams, the solid complexes of essential oils with α- and β-CyDs were prepared, and their molar ratios were found to be 1 : 2 (guest molecule/α-CyD) and 1 : 1 (guest molecule/β-CyD), respectively. X-Ray diffraction patterns of the complexes showed a typical channel type of crystal packing for both α- and β-CyD systems. Apparent stability constants (Kc') of β-CyD complexes were greater than those of α-CyD complexes, where the steric and hydrophobic factors of the essential oils appeared to be responsible for the magnitude of Kc'values. The volatility and photooxidation of essential oils were significantly retarded by the binding to CyDs. The improved thermal and photochemical stabilities of the essential oils through inclusion complex formation suggest the ease of handling with prolonged storage time.
