Poly(lactic acid)/ZIF-67 colorimetric headspace indicators for monitoring chicken breast freshness

Poly(lactic acid) (PLA)/zeolitic imidazolate framework-67 (ZIF-67) composite films were developed as intelligent indicators for monitoring chicken freshness through volatile amine detection. ZIF-67 particles, with an average particle size of 413 ± 104 nm and a BET surface area of 2163 m² g^-1, were incorporated into PLA at concentrations of 0.3-0.9 wt%. Film properties depended on ZIF-67 loading, with improved mechanical performance and reduced water vapor and apparent oxygen permeability at the intermediate concentration. The films exhibited rapid colorimetric responses to ammonia, dimethylamine, and trimethylamine, which are volatile basic nitrogen compounds formed during protein degradation. A perceptible color change (ΔE > 5) occurred within minutes of exposure. When applied as a headspace indicator to chicken stored at 23 °C, the film containing 0.6 wt% ZIF-67 showed a clear color transition corresponding to the increase in total volatile basic nitrogen, which exceeded the spoilage threshold of 30 mg N/100 g at approximately 36 h. These findings support PLA/ZIF0.6 as a non-contact headspace indicator label attached to the lid, not as a food-contact packaging film for monitoring poultry freshness.