Intelligent biogenic pH‐sensitive and amine‐responsive color‐changing label for real‐time monitoring of shrimp freshness

Abstract BACKGROUND This study developed an intelligent, pH‐sensitive and amine‐responsive colorimetric label based on chitosan, whey protein and thymol blue by controlling the pH value of the film‐forming solution. The obtained label was used to monitor shrimp freshness in real time. The results of this study offer a new approach for developing highly intelligent biogenic labels for freshness monitoring during seafood preservation and processing. RESULTS The pH 2.0 chitosan–whey protein–thymol blue (CWT‐pH 2.0) label exhibited remarkable properties, including the highest tensile strength (5.90 MPa), excellent thermal stability, low water solubility (27.80%) and highly sensitive color responsiveness. The characterization techniques of scanning electron microscopy, X‐ray diffraction and Fourier transform infrared spectroscopy confirmed the effective immobilization of thymol blue within the film‐forming matrix through hydrogen bonding. Furthermore, the CWT‐pH 2.0 label demonstrated visible color changes in the presence of volatile ammonia concentrations ranging from 25 to 25 000 ppm. Consequently, the label successfully facilitated real‐time monitoring of shrimp freshness during storage at 4 °C. Importantly, the release rate of thymol blue from the label in food simulants was minimal, measuring only 2.53%. CONCLUSION The CWT‐pH 2.0 label exhibits significant potential as a highly intelligent biogenic label for freshness monitoring in seafood preservation and processing. © 2023 Society of Chemical Industry.