Preparation of pH sensitive P-doped carbon dots-loaded starch/polyvinyl alcohol packaging film for real-time monitoring freshness of pork

Using biodegradable films as smart packaging to monitor the freshness of meat in real time is a promising and challenging work. Herein, the phosphorus-doped carbon dots (P-CDs) with pH sensitivity were coated on starch/ polyvinyl alcohol film (SP film) by a simple scrape-coating method and applied to monitor the freshness of pork. The P-CDs@SP film exhibits a uniform surface, excellent mechanical properties, higher light blocking. When the total volatile base nitrogen (TVB-N) of pork exceeded 15 mg/100 g, the color of the film changed from brownishyellow to purple-red, and the total color difference (Delta E) of the film obviously increased from 10.24 to 9.37 to 20.75 and 22.93 under the storage conditions of 25 and 4 degrees C, respectively. This can be attributed to the abundant hydroxyl groups on the surface of P-CDs and SP film to promote their stable binding through hydrogen bonds, which greatly improves the hydrophilicity of the films, providing conditions for the rapid conversion of the TVBN to ammonia and the formation of an alkaline environment. This work can simply and effectively monitor the freshness of pork through the changes of film color, will provide a new idea for the preparation of biodegradable smart packaging materials.