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 brownish-yellow to purple-red, and the total color difference ( ΔE ) 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 °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 TVB-N 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.