Enhancing the Structure, Optical, and Antimicrobial Advancements of Starch/Chitosan Blend Through Green-Synthesized SeO2 Nanoparticles and Their Application for Ras Cheese Packaging

Antimicrobial film (a film incorporated with antimicrobial agents) is a promising active packaging material that can extend the shelf life and maintain the quality of food products. In this work, selenium oxide nanoparticles (SeO₂-NPs) were green synthesized by halotolerant strain Bacillus subtilis EG5QL12 and then incorporated into a starch/chitosan (St/Cs) blend via the solution casting route. High-resolution transmission electron microscope (HR-TEM) revealed the spherical morphology of the prepared SeO₂-NPs, which is about 14 nm in size. X-ray diffraction (XRD) also confirmed the formation of nanosized crystalline SeO₂ and semicrystalline St/Cs blends. The main XRD peaks of the blend were shifted, indicating the complexation between St/Cs and the SeO₂ nanofillers. Fourier transform infrared spectroscopy (FTIR) spectra confirmed these structural changes in the blend, where the peaks became narrower and less intense. The field emission scan electron microscope/energy dispersive X-ray spectroscopy (FE-SEM/EDAX) analyses revealed the homogeneity between Cs and St and the steady distribution of Se inside the matrix. The St/Cs film exhibited high transmittance (87%) in the visible and IR ranges, significantly decreasing with increasing SeO₂-NPs content. The indirect/indirect optical band gap shrank from 4.7 and 5.4 eV to 3.9 and 4.9 eV, respectively. The green-synthesized SeO₂-NPs, blend, and nanocomposite demonstrated broad antimicrobial efficacy against gram-positive and gram-negative microorganisms. Of the checked microorganisms, Staphylococcus aureus was determined to be the most susceptible. Furthermore, Escherichia coli showed the least sensitivity to the solutions under study. The nanocomposite presented a highly significant influence on all examined microbes compared to both of its components alone, in addition to decreasing the amount used by both of them, due to the synergistic effect between chitosan and the SeO₂-NPs that have the ability to increase the concentration of reactive oxygen species (ROS) within cells, disrupt the microbial cell membrane, and inhibit the synthesis of protein, and nucleic acid. The coating of Ras cheese with the nanocomposite solution resulted in improving and preserving the chemical, and microbiological characteristics of the cheese produced.