Sodium alginate/chitosan-based intelligent multifunctional bilayer film for shrimp freshness retention and monitoring.

Developing bifunctional innovative food packaging for maintaining and monitoring food freshness is crucial for food safety. Here, we prepared tannic acid cinnamaldehyde nanoemulsions through self-assembly and ionic cross-linking between the natural emulsifiers tannic acid and cinnamaldehyde, and were incorporated into chitosan as a protective outer layer. Sodium alginate anchored with alizarin was employed as the sensing inner layer. A pH-sensitive bilayer film integrating real-time monitoring and maintenance of food fresh food freshness was designed using layer-by-layer assembly (LBL) technology. The prepared bilayer film exhibited 100 % UV protection, >99 % antimicrobial effect, and 94.86 % and 97.91 % clearance rates for DPPH and ABTS free radicals, respectively. In addition, the bilayer film exhibited high biosafety and sensitive, reversible, and rapid response to pH/NH. Shrimp preservation experiments showed that the smart bilayer film could effectively slow down the growth of microorganisms on the surface of shrimp, extend the freshness period of shrimp, and could monitor the freshness of shrimp in real-time through color changes. In conclusion, the prepared SL-CCT bilayer film has excellent potential for food preservation and freshness monitoring, providing a new perspective for design and development of multifunctional smart food packaging films.