Seaweed residue–derived carbon dots composite films for spoilage-responsive monitoring and preservation of large yellow croaker fillets

A multifunctional packaging film was developed by incorporating blueberry anthocyanins (BA) and seaweed-residue-derived carbon dots (CDs) into a chitosan/fish gelatin (CS/FG) matrix. The CS/FG/BA/0.1CDs film exhibited well-balanced rheology, UV shielding ability, and thermal stability. It also showed improved mechanical strength, enhanced structural uniformity, lower oxygen permeability (4.14 × 10^-11 g·m/(m²·s·Pa)), and superior antioxidant (ABTS: 97.15%; DPPH: 81.88%) and antibacterial activity. Importantly, the film displayed stable and visible colorimetric responses to pH (2-12) and ammonia vapor, enabling real-time freshness monitoring. When applied to large yellow croaker fillets stored at 4 °C, the film effectively delayed spoilage as indicated by reduced pH rise (6.89 ± 0.11), total volatile basic nitrogen content (28.9 ± 1.44 mg N/100 g), and microbial growth after 12 days. Treated samples also retained better texture, water-holding capacity, and sensory scores. These results demonstrate the synergistic effects of BA and CDs in supporting both preservation and intelligent monitoring, offering a sustainable packaging strategy for high-value aquatic products.