Functionalization of chitosan films using essential oils by supercritical CO2 impregnation method for various applications

Herein, chitosan films obtained by different approaches were functionalized with essential oils, i.e. mentha, clove, and cinnamon, by Supercritical Solvent Impregnation method to impart antioxidant and antimicrobial activity. The films were prepared from solutions with two different polymer concentrations (1 and 2.5 wt%) following three methodologies: casting and then drying at air (25 °C, 39 % relative humidity), casting and drying at 60 °C in humid conditions (82 % relativity humidity) and casting and water elimination by a freeze-drying process. The films were, then, characterized by scanning electron microscopy and X-ray diffraction, proving that the thickness, porosity, and crystallinity of the films are highly dependent on the preparation method. These structural variations affected the impregnation of essential oils by supercritical fluids, in terms of the amount and composition of the active compounds. Subsequently, yellowness, antioxidant and antimicrobial properties of the impregnated films were evaluated. The results demonstrated that the impregnated films retained high concentration of essential oils, especially the films impregnated with clove and produced by the freeze-drying process due to their higher porosity and lower crystallinity. These films also exhibited superior antimicrobial activity against Gram-positive and Gram-negative bacteria in comparison with the other two analyzed preparation methods.