Chitosan-based active films containing microwave-extracted Terminalia catappa leaf extract (TE) and hydrothermally synthesised zinc oxide were developed and characterised. The selected extraction condition (440 W, 20 min, followed by freeze drying) gave 29.5% extract recovery and a total phenolic content of 639.5 mg GAE/g extract. Structural analyses showed that the original crystalline ZnO phase was no longer detectable after film formation under acidic casting conditions, whereas zinc remained present in the film matrix, indicating acid-mediated dissolution and/or structural transformation during casting. Zinc-containing films exhibited higher tensile strength (up to 36.0 MPa), increased glass transition temperature (up to 122.9 °C), and reduced moisture content and water vapour transmission. TE contributed antioxidant activity and light-shielding properties, with antioxidant capacity reaching 22.1 mg Trolox/g film. Films containing ≥0.2% initial ZnO also showed disc-diffusion antimicrobial activity against Escherichia coli (up to 22.7 mm) and Staphylococcus aureus (up to 20.7 mm). A preliminary 7-day banana-wrapping study further suggested that intermediate formulations containing 0.1–0.2% TE and 0.2–0.3% initial ZnO provided a useful balance among mechanical performance, optical properties, antimicrobial activity, and visual preservation. Overall, zinc–polyphenol–chitosan interactions played an important role in governing film structure and functionality.
Thongchai et al. (Fri,) studied this question.