Comparative Study of Inclusion Complexes of Natural Terpineol, β-Sitosterol and Cholesterol with β-Cyclodextrin

DOS SANTOS, CRISTINA; MAZZOBRE, MARÍA FLORENCIA; BUERA, MARÍA DEL PILAR

Córdoba

Congreso; V Congreso Internacional de Ciencia y Tecnología de Alimentos (CICYTAC 2014); 2014

Cyclodextrins(CDs) are cyclic polysaccharides with a hydrophobic inner cavity and a hydrophilic outer surface that can encapsulate molecules to form host?guest supramolecular complexes. Since β-cyclodextrin(β-CD) is nontoxic and chemically stable, it can be used to increase the water solubility of hydrophobic ligands. The objective of present work was to study the ability of β-CD to encapsulate different non-polar ligands: terpineol, β-sitosterol and cholesterol. Stability constants of the encapsulation processes were obtained from phase solubility studies, physical properties and stability of the complexes during storage were also evaluated. The inclusion complexes were prepared by coprecipitation and freeze-drying method, using different ligands/β-CD molar ratios, temperatures and stirring times. Differential scanning calorimetry(DSC), infrared spectroscopy, magnetic nuclear resonance(NMR), X-ray diffraction and scanning electron microscopy (SEM) were used to confirm the formation of complexes. Phase solubility studies were carried out according to the Higuchi and Connors method to obtain the thermodynamic parameters involved in the formation of complexes using the Van?t Hoff equation. The sorption isotherms of β-CD and the complexes were obtained by the isopiestic method at 25°C. The analysis of the DSC thermograms confirmed that sitosterol and cholesterol were partially (40-60%) encapsulated in β-CD, depending on the experimental conditions, while terpineol was completely encapsulated.The aqueous solubility of the studied ligands increased with the presence of β-CD. The analysis of solubilities as a function of CD concentration gives rise to AL-type diagrams, indicating that complexes formed were of first order. The thermodynamic parameters of each ligand encapsulation were calculated. The negative values of ΔH and of G°25 indicate that the interaction processes between ligands/β-CD are exothermic and spontaneous in all cases. The relatively small enthalpy changes are typical of low energy interactions prevailing in complexes, like hydrophobic interactions and van der Waals forces. The presence of any of the ligands greatly modified the CD sorption curves; the amount of adsorbed water being smaller in the combined systems. The isotherms of the combined systems did not show a plateau, which indicates that no hydrates were formed and followed a sigmoid-type behavior with a marked increase of water content at more than 85% relative humidity(RH).The stability of the dehydrated complexes was influenced by water content and by ligand nature and structure. Terpineol remained included up to 60 days of storage, even at high RH. In the case of cholesterol and sitosterol, their inclusion increased as increasing RH and also the amount of CD in the systems. The obtained solubility, storage stability and thermodynamic data would be useful in the development of innovative food or pharmaceutical products requiring the addition of labile functional ingredients.