A novel colorimetric label based on ZnTPPS4/AG indicating pork freshness

A novel colorimetric indicator for pork freshness composed of agar, ZnTPPS 4 and glycerin was designed and developed by casting/solvent evaporation method. The FT-IR, UV-vis, XRD and SEM were employed to analyze the structure and valence bonds of ZnTPPS 4 /AG compound, and the results showed good compatibility between agar and ZnTPPS 4 . The tensile strength and elongation at the breaking point of indicator films increased slightly with increase of porphyrin, which may have been a contributing factor of H-bonds. After 7 days of placement, the total color variation ([Formula: see text]E) of major films was less than 5, manifesting in the color stability being sufficient enough to act as a color indicator, and the mechanism for color variation was explained therein. Furthermore, the prepared films were utilized as indicators for monitoring the freshness of lean meat at room temperature (25[Formula: see text]C). The total volatile basic nitrogen (TVB-N) of pork and [Formula: see text]E of the labels were recorded simultaneously. The trials demonstrated that ZnTPPS 4 /AG with higher content of ZnTPPS 4 had the superior sensitivity and the color changes of labels in pork packaging changed according to the decay threshold of TVB-N, which implied that ZnTPPS 4 /AG was able to indicate the spoilage via colorimetric method. Therefore, these novel indication labels could be used to monitor the pork freshness in a real-time, nondestructive and inexpensive way.