Bambara Groundnut Pericarp–Derived Carbon Dots: Reinforcement of Gelatin/PLA Bilayer Films and Their Function as Preservative in Packed Asian Seabass Slices

Conversion of agro-waste into carbon dots (CDs) transforms biomass into sustainable nanomaterials, enabling advanced applications in packaging and ensuring food safety. Bambara groundnut pericarp powder (BGPP) was hydrothermally processed at 200°C for varying durations (3-12 h) to synthesize BGP-CDs. BGP-CDs exhibited differences in size (1.34-15.02 nm), shape, and chemical composition, as characterized by transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) analyses. All samples exhibited excellent optical properties, including photoluminescence and UV barrier capability. Notably, BGP-CDs/3 (synthesized for 3 h) at 100 µg/mL demonstrated the highest UV-blocking efficiency against UV-A (35.62%) and UV-B (92.64%) lights. BGP-CDs synthesized for 12 h exhibited remarkable antimicrobial activities against selected species (Escherichia coli, Listeria monocytogenes, Aspergillus flavus, and Aspergillus parasiticus) due to their nanoscale size; however, their reduced size negatively impacted human cell viability. Antioxidant activity was highest in BGP-CDs synthesized for 6 h (BGP-CDs/6), as determined by different assays. Incorporating BGP-CDs/6 (4%, w/w) into gelatin/polylactic acid (PLA) bilayer film enhanced UV and water barrier properties, antioxidant capacity, and antibacterial efficacy compared to the control film. Additionally, Asian seabass slices (AS-S) packaged in pouches made from active bilayer film had the maintained color with negligible pH change. Microbial growth and lipid oxidation in AS-S were retarded as indicated by the lower rise in total viable count (TVC) and psychrophilic bacterial count (PBC) as well as thiobarbituric acid reactive substances (TBARS) values over 12 days of storage at 4°C. Thus, the developed multifunctional packaging film offers an innovative strategy that could impede the quality loss of perishable fish slices.