Interacción de compuestos fenólicos bioactivos con ciclodextrinas y polímeros de ciclodextrina

Resum

The present PhD Thesis investigates the interactions of two bioactive antioxidants present in virgin olive oil, tyrosol and caffeic acid, with cyclodextrins and cyclodextrin polymers. Firstly, the interactions of tyrosol with β-, methyl-β- and hydroxypropyl-β-cyclodextrin (HPβCD) have been analysed both in solution and in solid state. The stability constants of the complexes have been determined by UV-spectroscopy and fluorimetry. The characterization of the complexes in solid state has been carried out by X-ray diffraction and differential thermal analysis. Once complexation was verified, the influence of HPβCD on the antioxidant capacity and permeability through membrane of tyrosol and caffeic has been studied. The antioxidant capacity of tyrosol, determined by ORAC-fluorescein assays, increased in the presence of the cyclodextrin but that of caffeic acid experienced no change. The role of different cyclodextrins on the signal of the ORAC-fluorescein assay has been evaluated as well. The formation of inclusion complexes with HPβCD decreases the free fraction of the antioxidant and hence the permeability and flux through an artificial membrane. In addition, the sorption and release behavior of tyrosol and caffeic acid on polymeric systems based on cyclodextrins has been studied. Sorption is related to the extent of complexation of each antioxidant. The isosteric heats of sorption determined are higher at low coverages, in accordance with the heterogeneous nature of the polymers. Tyrosol presents higher isosteric heats than caffeic acid. Finally, it has been proved that diffusion is the predominant mechanism of antioxidants release from these cyclodextrin polymers. The microstructure of the polymers is in accordance with their respective release profiles.