Recording thermal history of pork meat by self-coloration gel

For real-time dynamic quality evaluation of pork meat, the thermal accumulation monitoring for the entire period is essential. The research aims to develop a novel covalent organic framework (COF) gel capable of recording such information. The COF with self-responsive irreversible color change property was synthesized using benzene-1,3,5-tricarboxaldehyde, 2,5-diamino-1,4-benzenedithiol dihydrochloride and p-phthalaldehyde as monomers. The thermal accumulation was monitored based on the COF over a broad temperature range (−22 °C–55 °C), which covered the storage temperatures of the pork meat. The results were easily readable by series visible color variations (yellow, green, blue and dark blue) displayed by COF during the thermal accumulation monitoring in the temperature range (25 °C–55 °C) of study. At the lower temperature (−22 °C–4 °C), small variation of the thermal information can be effectively represented by quantitative analysis. The color change rates were in the order of k_-22 °C < k_{4 °C} < k_25 °C < k_35 °C < k_55 °C. The activation energy of reaction was 65.31 kJ mol⁻¹. The indicator gel was prepared by the COF combining with carrageenan in pure aqueous medium. The potential application of the COF gel for real-time monitoring the dynamic quality change of pork samples was investigated. The response signals of the COF gel were well matched with the growth rate of microbe in pork meat. The proposed COF gel based thermal history indicator is promising for real-time monitoring dynamic quality changes of pork meat during the cold supply chain.