Synthesis Optimization of Chitosan-Derived Carbon Dots for Gelatin Capsule Waste/Gum Arabic Active Packaging Films

This study aimed to optimize the synthesis of chitosan-derived carbon dots (CS-CDs) and incorporate them into gelatin capsule waste/Gum Arabic (Gel/GA) composite films for sustainable active packaging of minced fish. CS-CDs were synthesized hydrothermally at 180, 200, and 220 °C for 4, 5, and 6 h. The optimal condition was 200 °C for 6 h, producing spherical nanoparticles below 10 nm with strong blue fluorescence, a maximum absorbance at 293 nm, and antioxidant activities of 56% (2,2-diphenyl-1-picrylhydrazyl: DPPH) and 66% (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid): ABTS) at a concentration of 20% (v/v), together with antibacterial activity against S. aureus, S. enteritidis, and E. coli. The optimized CS-CDs were incorporated into Gel/GA films at 0–2% (w/v), significantly increasing tensile strength from 2.20 to 4.19 MPa and improving water resistance (p < 0.05). Antioxidant and antimicrobial activities increased with CS-CD concentration. Gel/GA/CD-2 exhibited the best overall performance and effectively preserved minced fish at room temperature for up to 48 h by reducing microbial growth and lipid oxidation. Overall, integrating CS-CDs with upcycled gelatin capsule waste provides a promising approach for developing multifunctional biodegradable active packaging with enhanced mechanical, antioxidant and antimicrobial properties for seafood preservation.