Alginate-based multifunctional films incorporated with sulfur quantum dots for active packaging applications.

Sulfur quantum dots (SQDs) were fabricated using a facile hydrothermal method and used for the preparation of functional food packaging film and compared the properties with other sulfur-based fillers like elemental sulfur (ES) and sulfur nanoparticles (SNP). The SQDs have an average size of 5.3 nm and were very stable in aqueous suspension. Unlike other sulfur-based fillers, the SQD showed high antioxidant, antibacterial and antifungal activity, but no cytotoxicity was found for L929 mouse fibroblasts even after long-term exposure of 48 h. When sulfur-based fillers were added to the alginate film, SQD was more evenly dispersed in the polymer matrix than SNP and ES. The addition of SQD to the alginate film increased the film's UV barrier property by 82% and tensile strength by 18%. Also, the addition of SQDs to the films did not affect the stiffness (elastic modulus, EM) and water vapor barrier permeability (WVP) of the films. In addition, SQD-added films exhibited excellent antioxidant and strong antibacterial activity against bacterial (E. coli and L. monocytogenes) and fungal (A. niger and P. chrysogenum) food pathogens. When the film was applied as a bread packaging test, the SQD-added film prevented mold growth for 14 days, unlike the ES and SNP-added films.