Multifunctional carbon dots reinforced gelatin-based coating film for strawberry preservation

The development of safe, non-toxic, multifunctional nano preserved materials with excellent performance has become a hot research topic. Multifunctional Sophora Japonica extract (95% rutin)-derived carbon dots (R-CDs) were prepared by hydrothermal method. The π-π conjugation structure of R-CDs enabled them UV broadband absorption properties. The excellent antioxidant properties of R-CDs were attributed to the presence of the sp2 carbon in core and a large number of hydroxyl groups at the edges, and their degradation rate of potassium permanganate and scavenging activity of superoxide anion radical were better than that of ascorbic acid. The presence of CO bond may be the site for the generation of reactive oxygen species (ROS) and thus they could kill Staphylococcus aureus (S. aureus), Bacillus subtilis (B. subtilis) and Listeria monocytogenes (L. monocytogenes) at a concentration of 2 mg/mL and inhibited the growth of fungi (Botrytis cinerea). Then R-CDs were uniformly dispersed in gelatin-based solution, and the as-prepared films had smooth surface, good hydrophilicity, strong mechanical properties and good biocompatibility. With the increase of R-CDs addition, the tensile strength increased and then decreased, and the elongation at break rose to 358%. The film inherited the broadband UV absorption, antioxidant and antibacterial properties of R-CDs. The storage period of strawberries was prolonged after coating. The variety and abundance of microorganisms on the surface of strawberries was reduced and the growth of harmful bacteria was inhibited. This work provides more possibilities for the application of nanomaterials in fruit preservation.