A smart colorimetric film coupling deep eutectic solvents and deep learning for real-time Salmon freshness monitoring

Effective freshness monitoring is essential for aquatic products to ensure food safety and reduce waste. To overcome the limitations of stability and sensitivity in colorimetric films, we developed a novel composite film by integrating a tannic acid-Fe 2+ (TF) chelate with deep eutectic solvents (DESs) in a polyvinyl alcohol matrix. The TF chelate served as multifunctional indicator, providing distinct color responses to NH₃, DMA, and TMA while enhancing hydrophobicity, UV-blocking, and thermal stability. DESs incorporation significantly improved mechanical properties (elongation at break up to 600%) and drastically enhanced sensitivity, enabling visible color changes within 1 min due to increased surface roughness (1.78 to 3.97 nm), hygroscopicity (1.8% to 5.6% at 33% RH), and water vapor permeability (0.4 to 0.8 g·mm/(m 2 ·h·kPa)). In salmon monitoring, the film showed clear color transitions. Deep learning-assisted analysis achieved over 97% accuracy in freshness classification. Overall, the films show strong potential for freshness monitoring of aquatic products.