Freshness monitoring of some food products using pH-responsive smart films containing cyanidin cation

In this study, we introduced an innovative method by incorporating 1-butyl-3-methylimidazolium chloride (BmimCl) as a versatile component and fine-tuning the mixture of chitosan, BmimCl, and cyanidin cation (Anth) to create pH-responsive smart films for food freshness. Owing to the dual functionality of BmimCl, it served as a plasticizer as well as enhanced the film’s capacity to display a broader spectrum of visible color changes. The material properties of chitosan films containing BmimCl and Anth at varying concentrations were characterized using FTIR, XRD, mechanical test, TGA, UV-vis and pH sensitivity. The combined results indicate that the chitosan-based pH-responsive smart film possessed excellent mechanical properties, great thermal stability, high light transmission, and a broad pH sensitivity. pH-responsive films were used for real-time freshness monitoring of freshwater shrimps, sterilized milk, and hairtails. Results revealed that BmimCl disrupts the hydrogen bond network of chitosan molecules. The films exhibit a transition from green to red as the food turns from fresh to spoiled, effectively demonstrating their capability to monitor freshness.