Design and characterization of a pH-responsive intelligent active film for monitoring and preserving fish freshness.

An active intelligent packaging film (COL/CS/ZnO/ATH) was developed based on a collagen (COL), chitosan (CS), and nano-ZnO composite matrix, incorporating anthocyanins (ATH) extracted from red cabbage as a natural pH-sensitive indicator. FT-IR analysis and molecular docking revealed that the film's structure is governed by hydrogen-bonding interactions among ATH, collagen, and chitosan. The COL/CS/ZnO/ATH film exhibited excellent barrier properties, and high thermal stability, along with notable antioxidant and antibacterial activities. Compared with COL/CS film, the tensile strength, DPPH radical free, and ABTS radical free scavenging rate of the COL/CS/ZnO/ATH film had increased by 11.18 MPa, 71.09%, and 73.54%, respectively. Additionally, the film exhibited sensitive responses to both pH and ammonia variations. Application of the film to fish preservation demonstrated its efficacy, extending the shelf life by approximately 2 days. In addition, it allowed freshness to be monitored via observable color shifts. For quantitative assessment of this relationship, a smartphone app was used to extract RGB values, which were then correlated with both TVB-N and TVC. A linear regression model was established to predict changes in fish freshness. This multifunctional intelligent packaging system offers a simple and efficient approach for real-time food quality monitoring.