Development of ZnO based chitosan carboxymethylcellulose films containing Nigella sativa essential oil emulsion for feta cheese preservation

Lipid oxidation and microbial spoilage are major challenges limiting the shelf life of high-fat dairy products such as feta cheese. Active packaging systems incorporating natural bioactive compounds and inorganic nanoparticles provide a promising strategy to improve food preservation. This study aimed to develop an active bionanocomposite film based on chitosan–carboxymethylcellulose (Ch–CMC), zinc oxide (ZnO) nanoparticles, and a Nigella sativa L. essential oil submicron emulsion (NEN) for improving the preservation performance of feta cheese packaging during refrigerated storage. The effects of ZnO nanoparticles and NEN incorporation on the physicochemical, barrier, mechanical, morphological, and antimicrobial properties of the films were investigated. The incorporation of ZnO and NEN significantly (p < 0.05) improved film barrier properties by reducing water vapor permeability and limiting UV–visible light transmission, while increasing hydrophobicity and structural integrity. ZnO primarily enhanced tensile strength, whereas NEN improved film flexibility and elongation at break. The active films exhibited strong antimicrobial activity against Staphylococcus aureus , Escherichia coli , and Aspergillus niger , with inhibition zones reaching 25.89, 22.65, and 26.58 mm, respectively. Structural analysis revealed improved matrix compactness at optimized NEN concentrations, whereas excessive NEN incorporation promoted phase heterogeneity. During refrigerated storage, the active films also effectively suppressed microbial proliferation in feta cheese. After 45 days, mold and yeast counts were reduced from 3.13 log CFU/g in the control to 0.48 log CFU/g in cheese packaged with the film containing ZnO and 4% NEN, while detectable fungal growth was delayed by at least 15 days compared with the control. Overall, the developed ZnO–NEN bionanocomposite films exhibited improved barrier, mechanical, and antimicrobial performance, effectively preserving the microbiological quality and extending the shelf life of feta cheese.