Effect of hydroxypropyl-β-cyclodextrin and coadjuvants on the sorption capacity of hydrophilic polymer films for monoterpene alcohols

Chitosan films filled with hydroxypropyl-β-cyclodextrin at a 1:1 weight ratio and plasticized with 35 or 50% glycerol or 35% propylene glycol were prepared by casting and conditioned at different relative humidities to achieve a similar water content. Sorption properties of the films for various monoterpene compounds with phenolic, or with linear or cyclohexyl alcohol structures were studied after their immersion in the volatile liquids. In general, the films presented a considerable capacity to retain monophenolic compounds, with sorption values ranging from 455% for meta-cumenol to 193% for guaiacol, for chitosan films with the same formulation. These values were two orders of magnitude higher than those of compounds without the phenol group. The affinity for monophenolic compounds decreased in films plasticized with hydrophilic propylene glycol, whereas no changes were observed in the retention of non-phenolic monoterpenes. Replacement of chitosan with polyvinyl alcohol polymer considerably decreased the retention of monophenolic compounds, with the exception of isoeugenol. Finally, the antimicrobial activity of monoterpenes and films loaded with them was evaluated in vitro by the microatmosphere test against Escherichia coli and Staphylococcus aureus. The present study shows that hydroxypropyl-β-cyclodextrin and the plasticization level achieved by hydrophilic films can be used to regulate loading capacity and sorption selectivity of naturally occurring antimicrobial compounds.The authors acknowledge financial support from the Spanish Ministry of Economy and Competitiveness (MINECO, AGL2012-39920-C03-01 and AGL2015-64595-R projects). Laura Higueras thanks the Spanish National Research Council for a JAE-PreDoc Fellowship.Peer reviewe