Films for salmon freshness monitor, prepared with lipophilic soy protein, hydroxypropyl methylcellulose, and octadecenylsuccinic anhydride-modified γ-cyclodextrin-MOF loaded with shikonin

The development of smart packaging films has attracted considerable attention for their ability to keep track of the freshness of aquatic products. Incorporating natural pigments into edible films has emerged as a promising food freshness assessment approach. However, the limited stability and poor dispersion of natural pigments in film-forming solutions pose challenges to their practical applications in food. Herein, shikonin, a natural pigment, was successfully encapsulated within the pores of octadecenylsuccinic anhydride (ODSA) modified γ-cyclodextrin metal-organic frameworks (OCM). Subsequently, shikonin-loaded OCM (OCM-shikonin) was integrated into soy lipophilic protein/hydroxypropyl methylcellulose-based films (LP/HPMC films). The results demonstrated that the loading OCM-shikonin significantly enhanced the structural and functional characteristics of LP/HPMC films. Notably, the encapsulation rate of shikonin by OCM was 60.12 % ± 0.83, and its storage stability for 7 d was 1.5 times as high as that of free shikonin. The OCM-shikonin were evenly distributed within the LP/HPMC film matrix, resulting in improved mechanical properties, UV-blocking capability, and water vapor barrier properties of the LP/HPMC film. Additionally, the prepared LP/HPMC films loaded with OCM-shikonin (OCM-shikonin films) exhibited pH and ammonia sensitivity, enabling them to effectively monitor the freshness of salmon during storage. Furthermore, a deep-learning model was established to correlate the Total Volatile Basic Nitrogen (TVB-N) levels in salmon with color changes of the films. Among these models, the Xception model demonstrated a high accuracy of 0.9973, highlighting the potential of these films for real-time, reliable freshness monitoring. In conclusion, the OCM-shikonin films possess excellent pH-responsive properties, making them highly applicable for smart packaging in food safety and quality control. • The adsorption of shikonin on γ-CD-MOF is facilitated by ODSA modification. • The shikonin in ODSA modification γ-CD-MOF (OCM) exhibits excellent stability. • A pH-sensitive smart packaging film was fabricated by doping LP/HPMC with OCM-shikonin. • The OCM-shikonin film could be used to monitor the freshness of salmon. • The Xception model has the best potential to monitor the freshness of salmon.