Development of a pH‐sensing indicator for shrimp freshness monitoring: Curcumin and anthocyanin‐loaded gelatin films

An intelligent pH‐sensing indicator containing Roselle (Hibiseus sabdariffa L.) (RS) anthocyanin and curcumin (CR) was developed and characterized as on‐package indicator tags to check the freshness of shrimp during the storage at 4°C. FE‐SEM and FT‐IR analysis showed that RS and CR were successfully immobilized in the gelatin–glycerol film‐forming substrate. The addition of various natural dyes increased the thickness and antioxidant action of the colorimetric film. To assess the response to changes in the pH, the colorimetric film was immersed in different buffers. Based on volatile amines secreted by shrimp, a test application of a colorimetric film containing natural dyes at a ratio of CR:RS = 1:4 (v/v) was conducted in shrimp at 4°C. The total volatile basic nitrogen (TVB‐N) and the pH of shrimp were monitored during refrigerated storage for 10 days, and the color changes of the indicator were recorded simultaneously. The results indicated that the designed colorimetric film could produce various colors, which are thought to be indicative of the freshness and spoilage of packaged shrimp. Therefore, the target film can be utilized as a promising smart packaging material for monitoring the freshness of shrimp and aquatic products in real time. Results indicated that a mixture of curcumin and anthocyanin could be a good indicator material for intelligent film to nondestructively monitor the freshness of shrimp.