Cellulose nanofiber-based coating film integrated with nitrogen-functionalized carbon dots for active packaging applications of fresh fruit

Carbon dots were synthesized using a hydrothermal method with glucose as the carbon source (GCD) and functionalized with nitrogen. The GCD and N-functionalized carbon dots (NGCD) were used to prepare cellulose nanofiber (CNF)-based composite films. GCD and NGCD provided high UV blocking properties to the CNF film without changing the transparency, reducing the T280 by 91–98 % and T660 by 12−10 %. The addition of GCD and NGCD did not affect the mechanical properties but increased the film's water vapor permeability (WVP) and water contact angle (WCA). The composite films also showed high antioxidant activity with 99−99 % of ABTS and 80–85 % of DPPH radical scavenging activities. The CNF-based films with GCD generated reactive oxygen species (ROS) to exhibit high antimicrobial activity; however, the CNF/NGCD film showed stronger antibacterial and antifungal activity than the CNF/GCD film. In addition, the CNF-based films incorporated with GCDs showed negligible cytotoxicity. When tangerine and strawberry fruit were coated with the CNF-based coating solutions, the fruit coated with CNF/NGCD inhibited fungal growth on the fruit surface, extending their shelf life by more than 10 and 2 d, respectively. The CD-added CNF films with high antioxidant, antimicrobial, and low cytotoxicity are likely to be used for antifungal coating of fresh fruit and active packaging applications.