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

Abstract

A novel colorimetric indicator for pork freshness composed of agar, ZnTPPS4 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 ZnTPPS4/AG compound, and the results showed good compatibility between agar and ZnTPPS4. 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 ZnTPPS4/AG with higher content of ZnTPPS4 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 ZnTPPS4/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.