Nanocellulose-enhanced smart film for the accurate monitoring of shrimp freshness via anthocyanin-induced color changes

Smart films allow consumers to visually determine food freshness. We aimed to improve the surface contact area of gas permeation in anthocyanin (AH)-induced smart films by introducing nanocellulose (NC) prepared by sulfuric acid (CNSA), citric acid (CNCA), and TEMPO (CNF) to improve their sensitivity. The film matrix was composed of PVA. The structure, functionality, and sensitivity of films were compared. The results showed that films incorporating CNSA and CNCA had larger surface areas and stronger intermolecular interactions. Sensitivity tests showed a color change from blue-violet to yellow in PVA/AH-CNSA and -CNCA films at 131 ppm of ammonia, occurring within 4 min of exposure. Shrimp freshness was further monitored using the films, with three stages of shrimp freshness (fresh, sub-fresh, and spoiled) differentiated clearly via distinct color changes. A strong correlation between freshness indexes and color parameters was established. The PVA/AH-CNSA and -CNCA films are suitable for real-time monitoring seafood freshness.