Effect of sulfur nanoparticles on properties of alginate-based films for active food packaging applications

Sulfur nanoparticles (SNPs) were prepared and embedded in calcium cross-linked alginate films in varying concentration, and their effect on the functional properties of the films were studied. The FE-SEM image showed uniform dispersion of up to 2 wt% of SNPs, above which aggregation was observed. The addition of 2 wt% of SNPs showed the best results of the tensile and water vapor barrier properties, with an increase in 12% and 41%, respectively. The surface color of the films changed significantly by the addition of SNPs with a decrease in transparency. However, the UV barrier properties showed a considerable increase of 99%. In addition, the incorporation of SNPs increased the hydrophobicity of the film, which was evident by the increased water contact angle and decreased moisture content of the film, as indicated by the thermal analysis results. The antimicrobial activity of alginate/SNPs composite film was tested against foodborne pathogenic bacteria, E. coli and L. monocytogenes. The nanocomposite film did not completely destroy E. coli but showed a bacteriostatic activity to reduce the 60% of bacterial colonies. However, the activity against L. monocytogenes was found to be highly bactericidal at the highest nanoparticle concentration, where a 100% bacterial elimination was observed after 12 h of exposure. Thus, the alginate/SNPs composite film can be used for the packaging of frozen foods with high moisture content that are susceptible to Listeria monocytogenes contamination, such as meat products.

Automated summary

Sulfur nanoparticles embedded in calcium cross-linked alginate films improved the tensile and water vapor barrier properties, as well as increased UV barrier properties and hydrophobicity of the films. The nanocomposite film exhibited antimicrobial activity, with bacteriostatic effects against E. coli and highly bactericidal effects against L. monocytogenes.