Abstract: An intelligent indicator film was prepared with chitosan (CS) and sodium alginate (SA) as film-forming material with added black apple peel anthocyanin (BAA). The effects of different concentrations of BAA on the microstructure, thickness, color, mechanical properties, moisture content, and ultraviolet (UV) transmittance of the composite film were analyzed and compared. In addition, the feasibility of applying the composite film for monitoring shrimp freshness was studied. The results showed that addition of BAA made the components of the composite film interact with each other. BAA was well dispersed in the composite film, which significantly improved the mechanical properties of the composite film, and reduced its water content and UV transmittance. Furthermore, the color of BAA changed from red to yellow in the pH range of 1–14, which showed an obvious respond to pH. The composite film containing 15% BAA was sensitive to pH and thus could be used for monitoring shrimp freshness. On the 5th day of storage at 4 ℃, the total volatile basic nitrogen (TVB-N) content and pH of shrimp exceeded the spoilage threshold, indicating shrimp spoilage, and the color of the film changed from red to dark gray. Therefore, CS-SA composite films can be used as a good carrier for BAA to prepare an intelligent indicator film for shrimp freshness monitoring.

Key words: intelligent indicator film; chitosan; sodium alginate; black apple peel; shrimp freshness