Biodegradable active packaging films based on methyl cellulose/chitosan nanofibers and turnip peel carbon dots for perishable food preservation

Abstract

Active food packaging system extends the longevity of products and preserves their quality by incorporating functional additives. In this study, the transparent and multifunctional composite films from methylcellulose/chitosan nanofibers (MC/ChNFs) matrix were produced via casting method by adding carbon dots (CDs) prepared using turnip peel bio-waste (TPCDs; 1, 3, and 5 wt%). Here, TPCD was incorporated into biopolymeric films to provide improved physic-mechanical, microstructural, and functional properties. TPCD is well dispersed in MC/ChNFs matrix, and each moiety is hydrogen bonded with the other. Thus, the incorporation of TPCDs 3 wt% into the films reduced water vapor permeability (3.4 → 2.9 × 10⁻¹¹ g.m/m².s.Pa), moisture content (36.62 % → 21.77 %), and water solubility (56.12 % → 39.12 %), while tensile strength (22.56 → 28.05 MPa), elongation at break (42.57 % → 49.14 %), and water contact angle (46.6°→ 50.6°) presented the opposite trend. In contrast, the film containing 5 wt% TPCDs had slightly lower physic-mechanical properties. The biopolymer films containing higher TPCDs (5 wt%) indicated favorable functional properties, including good antimicrobial activity against S. aureus (21 mm) and Escherichia coli (15 mm) strains, which arises from the reactive oxygen species (ROS) generated by TPCDs, effectively inhibiting microbial growth. The proposed films also indicated excellent antioxidant properties (DPPH•; 88 %) and proper UV protection (96 %), contributing to extended shelf life and quality preservation of packaged food in real application. The application of films in real food packaging showed that 5 wt% TPCDs-rich MC/ChNFs film maintained the freshness and visual quality of APPLE up to 5 d at 4 °C. Also, the film containing 5 % TPCDs increased the shelf life of minced red meat up to 8 d Therefore, this active film is an environmentally friendly packaging that increases safety, durability, and quality of perishable foods.