Impact of tea tree essential oil and citric acid/choline chloride on physical, structural and antibacterial properties of chitosan-based films

The purpose of this study was to develop a novel antimicrobial packaging film by using chitosan (CS), deep eutectic solvent (DES, a plasticizer) and tea tree essential oil (TTO, a natural antibacterial agent). The physical properties of the films (i.e., water content, solubility, water vapor permeability, color, thickness, water contact angle, and mechanical properties) demonstrated that TTO reduced the hydrophilicity of the films. At the same time, DES significantly improved the flexibility of the films. Micro-structural characterization showed that DES and TTO interacted with the CS matrix and were uniformly dispersed in films. The interactions among these main components in the films were verified by Fourier transform infrared spectroscopy and X-ray diffraction analysis. Thermogravimetric analysis further confirmed that these films had good thermal stability. In addition, the antibacterial assays verified that the CS-DES-TTO films could inhibit the activity of planktonic Sh. flexneri. The films prepared in this study showed the characteristics required of active packaging materials.