Development of halochromic labels based on binary systems of cationic guar gum and κ-carrageenan loaded with alizarin red S for monitoring milk and seafood freshness

Monitoring of food quality, in particular, high-protein food quality, is an important component in ensuring food safety and human health. In this research, a feasible and easy solution casting and solvent evaporation strategy was adapted to fabricate alizarin red S (ARS)-loaded halochromic cationic guar gum (CGG) and κ-carrageenan (CAR) blend packaging labels to improve its good physical strength, multifunctional acid–base responsive characteristics, and water barrier properties. The findings indicated that incorporating CAR at 40% polymer solid mass achieved higher tensile strength (21.0 ± 1.77 MPa), water resistance (29.92 ± 6.61% solubility), and thermal stability, which can be attributed to good compatibility between CGG and CAR. The results obtained from FT-IR, XRD, and SEM analyses demonstrate that the incorporation of ARS exhibits non-covalent bonding with the polymer blend matrix through electrostatic interactions and hydrogen bonding, thus reducing its crystallinity and restructuring the CGG-CAR matrix disorderly. The prepared indicating label films presented visual recognition of ammonia and trimethylamine (TMA-N) at 0.008 mM in 6 min (the total color difference (ΔE) for TMA-N is>11.89), and can be reused at least six times. Moreover, the color of ARS at different pH values remains persistent for at least 180 days. The practical applications show that the films, as indicator labels, can realize real-time, accurate, and visual dynamic monitoring of seafood (shrimp) and milk by engendering three chromatic stages discernible by the naked eye (fresh, spoiling, and spoiled). The ΔE for monitoring sub-fresh milk and shrimp reached as high as 14.91 and 13.32, respectively.