Preparation of a highly-sensitive intelligent label based on MOFs and its application in visual monitoring of pork freshness

To achieve non-destructive and real-time monitoring of pork freshness, an intelligent indicator label was developed using nanoparticles of cyclodextrin metal–organic frameworks (CD-MOFs) loaded with curcumin (Cur), referred to as CC-MOFs. The study investigated its application in the visual monitoring of pork freshness. The microstructures, chemical compositions, and thermal stability of CC-MOFs, as well as the responsiveness of the intelligent indicator label, were explored. Additionally, the feasibility of the indicator label for monitoring pork freshness was studied. The results demonstrated that in the CC-MOFs particles prepared via the green synthesis method, Cur was successfully embedded into the CD-MOFs pores via hydrogen bonding. This induced local reconstruction of the MOF framework, forming a porous structure with a rough surface, which significantly improved color persistence and stability. The CC-MOFs label responded sensitively to volatile ammonia, performing significantly better than the pure Cur label. In the pork storage model, the CC-MOFs label changed from khaki to orange-red and then to reddish-brown. The color changes were highly correlated with spoilage indicators such as TVB-N value, pH value, and electrical conductivity, and were consistent with electronic nose detection results. In summary, this intelligent indicator label can accurately distinguish three freshness levels of pork, providing a non-toxic and efficient visual solution for real-time food freshness monitoring.