Novel Co-MOF-doped gelatin/agar intelligent film for beef freshness visual tracking based on the structural change of...

It is an important task to construct intelligent packaging for meat freshness monitoring with good color stability and indication function. Herein, cobalt-based metal-organic framework nanomaterials (Co-MOF, ZIF-67) with antimicrobial and ammonia-sensitive properties were successfully synthesized and added into gelatin/agar (GA) matrix to develop highly stable intelligent films (GA/ZIF67). The incorporation of ZIF-67 nanoparticles enhanced the hydrophobicity (water contact angle >90°) and UV-blocking properties (close to 0.3 % at T280) of the films and endowed the films with excellent antimicrobial activity. The GA/ZIF67 films exhibited outstanding ammonia-sensitive functionality and color stability. More crucially, the ammonia-sensitive color-changing mechanism of ZIF-67 may be attributed to the slow etching effect of its crystal facets upon exposure to ammonia. With the gradual spoilage of beef, the color of the GA/ZIF67 film changes from blue-violet to gray-yellow/orange-red. In addition, the RGB value of the film collected by a mobile device App was used to quickly determine the freshness of beef, reducing individual variability in color perception. Overall, this work offers novel insights into exploring Co-MOF as a new type of indicator for developing a rapid and real-time beef freshness monitoring system, which has great potential for application in the intelligent packaging field.