Comprehensive characterization of active chitosan-gelatin blend films enriched with different essential oils

Natural extracts and plant essential oils (EOs) have long been recognized as valid alternatives to synthetic food additives owing to their proved wide-spectrum antimicrobial capacity. The main aim of this study was to characterize the physical, mechanical, water barrier, microstructural and antimicrobial properties of chitosan-gelatin blend films enriched with cinnamon, citronella, pink clove, nutmeg and thyme EOs. The film microstructure determined by scanning electron microscopy, showed that all active films had heterogeneous surface: in particular, films including cinnamon, nutmeg and thyme EOs showed remarkable pores on the surface. The possible interaction of chitosan-gelatin blend film with incorporated EOs was investigated using Fourier-transform infrared (FT-IR) spectroscopy. Presence of new bands and changes in the FT-IR spectra confirmed intermolecular interactions between the chitosan-gelatin matrix and the EOs. The antimicrobial activity of films was determined using the disk diffusion assay. Active films inhibited the growth of four major food bacterial pathogens including Campylobacter jejuni, Escherichia coli, Listeria monocytogenes and Salmonella typhimurium and, among the tested EOs, thyme was the most effective (p < 0.05). The active films can be considered as effective barriers against UV light. The incorporation of EOs to the chitosan-gelatin film increased thickness, moisture content, water vapor permeability, b(star) and Delta E-star values (p < 0.05) while it decreased L-star value, light transparency and opacity (p < 0.05). Overall, the characterization of functional properties revealed that chitosan-gelatin films incorporated with EOs could be used as environmentally friendly active food packaging with antimicrobial properties and potential to extend the shelf-life of food products.