Development of sustainable and active food packaging films based on alginate enriched with plant polyphenol carbon dots and layered clay.

Natural polymer based food packaging has attracted more and more attention, but the lack of active functions of natural polymer hinders its application in the field of active packaging. In this study, chlorogenic acid carbon dots (CGA-CDs) was synthesized mildly using natural plant polyphenol CGA as carbon source, and CGA functionalized layered clays (LDHs@CGA) was introduced as reinforcing agent. Alg active films were fabricated by solution casting method using natural polysaccharide-alginate (Alg), CGA-CDs and LDHs@CGA. The results showed that the average particle size of the synthesized CGA-CDs was ∼2.0 nm, with obvious graphitized structure inside and active groups (-OH and -NH, etc.) outside, showing obvious UV absorption and antibacterial activity. With the addition of CGA-CDs, UV barrier, antibacterial, thermal stability, hydrophobicity and flexibility of Alg active films were significantly improved. When the amount of CGA-CDs reached 2 %, UV transmission (280 nm) and of Alg active films was only 2.66 %, which was reduced by 88.1 % compared with pure Alg film. The highest antibacterial rate against Escherichia coli and Staphylococcus aureus reached 86.0 % and 91.6 %, respectively. Freshness preservation experiment of fresh-cut apples indicated that Alg active coating incorporating CGA-CDs maintained the lowest browning index and mildew. These results indicate that the excellent active functions of CGA-CDs can promote the application of Alg matrix in the field of natural polymer active packaging.