A colormetry-enhanced and highly pH-responsive smart film using 1-butyl-3-methylimidazolium chloride as tuner for monitoring grass carp freshness

This study developed an innovative colorimetric film by incorporating 1-butyl-3-methylimidazolium chloride (BmimCl) in a composite matrix containing red cabbage anthocyanins extract (RCAE), ferulic acid (FA), gellan gum (GG), and potato starch (PS) for real-time grass carp freshness detection. A comprehensive analysis was conducted on the rheological characteristics of film-forming solutions, mechanical properties, hydrophobicity, opacity, characterization of structure, sensitivity, and color stability of smart film. Significantly, the introduction of BmimCl led to multifaceted enhancements in film performance. The findings indicated that the flexibility of films added with BmimCl was enhanced and the elongation at break (EAB) was increased from 20.34 % to 28.36 %. The surface of films was smoother and denser, and the surface roughness was reduced from 1.7 μm to 1.2 μm. The peak intensities of the XRD and FT-IR patterns of films changed, indicating the formation of hydrogen bonds between BmimCl and film substrates. The GGPS-R-FA-B4 film presented the most pronounced color change in different pH environments and the most sensitive response to the variation of ammonia concentration in the environment. The color of GGPS-R-FA-B4 film exhibited a strong correlation with the quality change of fish, which could be used to distinguish the freshness, sub-freshness, and spoilage of grass carp. This study provided an effective method to enhance the accuracy and sensitivity of smart films for monitoring food freshness.