Sorption and Release of Natural Phenolic Antioxidants in Different Cyclodextrin Polymers

The sorption and release of tyrosol and caffeic acid, two biophenolic antioxidants with known health benefits, in different insoluble cyclodextrin polymers have been studied. Cyclodextrin polymers were synthesized by cross-linking β-cyclodextrin or 50:50 w/w nominal mixtures of α- and β-cyclodextrins using either epichlorohydrin (EP) or toluene-2,4-diisocyanate (TDI) as cross-linking agents. An analogous sucrose polymer was prepared using EP as cross-linking reagent. Freundlich isotherms and isosteric heats of sorption for tyrosol and caffeic acid in the insoluble β-cyclodextrin polymer cross-linked with epichlorohydrin at 50 °C were obtained and discussed. Finally, the release of tyrosol and caffeic acid has been studied from loaded polymer disks, the microstructures of which were characterized by mercury intrusion porosimetry. Caffeic acid shows greater affinity than tyrosol for the polymeric matrices as it presents a higher sorption and a lower and slower release. However, tyrosol has a higher isosteric heat of sorption for low coverages.