Properties of Roselle and alizarin mixed loaded gelatin films as a pH‐sensing indicator for shrimp freshness monitoring

An intelligent pH‐sensing indicator containing Roselle (Hibiscus sabdariffa L.) (ROS) anthocyanin and alizarin (ALZ) was developed and characterized as on‐package indicator tags to check the shrimp freshness during the storing at 4°C. Fourier transform infrared (FT‐IR) analysis showed that ROS and ALZ were successfully immobilized in the gelatin–glycerol film‐forming substrate. The addition of various natural dyes enhanced the thickness and antioxidant action of the colourimetric film. To assess the response to changes in the pH, the colourimetric film was immersed in different buffers. Based on volatile amines secreted by shrimp, a test application of a colourimetric film containing natural dyes at a ratio of ROS:ALZ = 4:1 (v/v) was conducted in shrimp at 4°C. The findings indicated that the designed colourimetric film could produce various colours, which are thought to indicate 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.