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Recently, Professor Xiangning Chen's team from the Key Laboratory of Agricultural Product Processing and Quality Control (Co-construction by Ministry and Province), Ministry of Agriculture and Rural Affairs Beijing of our university, published a research paper titled "pH-responsive color indicator film based on gelatin/chitosan cross-linking with anthocyanin-Fe²⁺ chelate for pork freshness monitoring" in the authoritative journal in the field of food, "Food Hydrocolloids" (Chinese Academy of Sciences (CAS) 1st Quartile, IF=11.0). The study, through cross-linking polymerization reactions and various characterization techniques, deeply explored the stability and color response characteristics of anthocyanin-Fe²⁺ chelate in gelatin/chitosan matrix, and the intelligent film prepared with natural anthocyanins showed high sensitivity to ammonia produced by meat. This provides an innovative solution for monitoring the freshness of chilled pork.

Structural changes of BA and BA-Fe²⁺ after binding with the matrix

Comparison of atomic force microscopy images of surface roughness for films with different components

Color changes and sensitivity comparison of films with different components in ammonia vapor

The study achieved the binding of anthocyanin indicator with the film matrix through hydrogen bonds between the hydroxyl groups of the chelate and the hydroxyl, amino, and ester groups in the cross-linked matrix, giving the intelligent indicator film good stability. The addition of BA-Fe²⁺ and its interaction with other components in the film improved the film's stability under high-temperature conditions and its barrier to oxygen, protecting the pH indicator from oxidation. The indicator film also has certain antioxidant and antibacterial activities. In the storage experiment of chilled pork, the indicator film changed from rose red to dark red, then gradually to purple and blue. Purple indicates an early spoilage warning, and a further change to blue indicates that the meat is no longer suitable for consumption.

Haolan Zhao, a master's student from the College of Food Science and Engineering, is the first author of the paper, and Professor Xiangning Chen and Dr. Hongru Zhang are the corresponding authors of the paper.