Quaternized chitosan-based nanofibers with strong antibacterial and antioxidant activity designed as ecological active food packaging

The paper presents a novel design for nanofibers specifically tailored for food packaging applications. To this end, chitosan, quaternized chitosan, vanillin and poly(ethylene oxide) were electrospun into fibrous materials, having in mind the benefits brought by the (i) natural origin of the bioactive components, (ii) high surface-area-to-volume ratio of nanofibers and (iii) dynamic nature of the imine bonds. The investigation of the physicochemical characteristics by FTIR and 1H NMR spectroscopy, X-ray diffraction, SEM and polarized light microscopy confirmed the bonding of vanillin via dynamic imine units, strong intermolecular forces amongst the components and formation of fibers with average diameter of 140 nm. These features enabled high mechanical properties in terms of tensile strength, elongation at break, and Young's modulus, thermal stability, and good moisture adsorption. The encapsulation of vanillin by covalent imine bonds and the inclusion of quaternized chitosan endowed the fibers with high antioxidant, antibacterial and antifungal activity against relevant strains, such as E. coli, S. aureus and C. albicans. As a proof-of-concept, their application on raspberries as model fruits significantly extended the shelf life to 7 days under atmospheric conditions, confirmed by the physico-chemical and microbiological evaluation of the fruits. The natural origin of the components promoted fast biodegradation in soil in less than 7 weeks. All these data show that the studied imino-chitosan/quaternized chitosan-based nanofibers are valuable materials that meet the requirements for ecological active food packaging.