Preparation and characterization of pH-sensitive intelligent films based on carboxymethyl chitosan and sodium alginate for preservation monitoring

Bio-based intelligent film materials have emerged as an effective alternative to traditional petroleum-based food packaging. In this study, different proportions of procyanidins and curcumin were incorporated into carboxymethyl chitosan and sodium alginate solutions, and pH-sensitive intelligent packaging films were successfully prepared by solution-casting method for monitoring freshness and shelf life of food. Compared with the thickness of film without active compounds (92.67 μm), the addition of procyanidins and curcumin made the thickness of films reach 99.67–105.80 μm, and the total dissolved mass and swelling rate decreased. Hydrogen bonds and electrostatic interaction among procyanidins, curcumin, carboxymethyl chitosan and sodium alginate also effectively improved the mechanical properties of films. The films had good UV barrier properties, and their opacity were higher than 10%. When the concentration of procyanidins and curcumin was higher than 25 μg/mL, the radical scavenging ability of DPPH and ABTS of the prepared films could reach more than 50%, and the films had effective inhibitory effects on Escherichia coli and Staphylococcus aureus. Moreover, due to the presence of procyanidins and curcumin, the prepared film-forming solutions and films showed different colors in the pH range of 2–12. The application of pH-sensitive films on food could reflect the quality and freshness of shrimp, and effectively prolong the shelf life of grapes. The prepared film also had the advantages of biodegradability and environmental friendliness, which was of great significance for replacing petroleum-based materials and promoting food safety.