Development of ammonia-sensitive carboxymethyl cellulose/pectin colorimetric films with sodium lignosulfonate-regulated ZIF-67 for pork freshness monitoring

Volatile amines generated during meat spoilage provide direct chemical signals for freshness evaluation, but rapidly translating these signals into stable visual responses remains a challenge. Herein, a rapid colorimetric indicator film was developed by incorporating sodium lignosulfonate-regulated ZIF-67 (ZIF-67@SLS) into a sodium carboxymethyl cellulose/pectin (CP) matrix. Modification with SLS endows ZIF-67 with a surface that exhibits greater affinity for amine compounds, thereby enabling it to interact more efficiently with volatile amines associated with meat spoilage. After integration into the CP matrix, CP/ZIF-67@SLS-5% achieved a ΔE of 19.72 after 10 min of NH 3 exposure, representing an 83.8% increase compared to CP/ZIF-67 (ΔE = 10.73), indicating a faster and stronger ammonia-responsive color transition. Meanwhile, the CP/ZIF-67@SLS-5% film maintained good color stability during 21 days of storage at 4, 25, and 50 °C, with ΔE values remaining below 5. The optimized CP/ZIF-67@SLS-5% film also exhibited improved mechanical and barrier performance, with tensile strength and elongation at break reaching 6.49 ± 0.08 MPa and 46.10 ± 2.04%, respectively, and water vapor transmission rate decreasing to 767.71 g m −2 d −1 . When applied to pork freshness monitoring at 4 and 25 °C, the CP/ZIF-67@SLS-5% film displayed visible color transitions from pale purple to brown during storage, enabling timely visual indication of pork spoilage. This work demonstrates that SLS-regulated ZIF-67 can serve as a response-active colorimetric unit for developing rapid ammonia-responsive indicators toward meat freshness monitoring.