Thermal, Mechanical, Microstructural and Inhibitory Characteristics of Sodium Caseinate Based Bioactive Films Reinforced by ZnONPs/Encapsulated Melissa officinalis Essential Oil

Abstract

Sodium caseinate (SC) based active edible films containing a mixture of zinc oxide nanoparticles (ZnONPs) and microcapsules of Melissa officinalis essential oil (MMEO) were prepared, and their characteristics were investigated. MMEO was used at concentrations of 0, 5 and 10% w/v and the amounts of ZnONPs were 0, 0.01, and 0.03% w/v. Central composite design (CCD) was utilized to optimize the effects of MMEO and ZnONPs on the biopolymer. The mechanical test results demonstrated that increasing MMEO and ZnONPs concentrations increased tensile strength. Morphological results showed that the prepared microcapsules were homogeneously spherical in the sodium caseinate film, and the nanoparticles were evenly dispersed. Fourier transform infrared spectroscopy (FTIR) results exhibited the compatibility between SC and nanocarriers. The results of X-ray diffraction (XRD) analyses indicated that nanocomposite films had higher crystallinity than pure films of SC. The results of differential scanning calorimetry (DSC) showed that dissociation of the intramolecular bond as well as the melting of the crystalline regions caused endothermic peaks in these compounds. The prepared films presented high antioxidant properties and the antibacterial behavior of the films was improved by incorporation of MMEO and ZnONPs into the films. The optimized film fabricated in this study had a practical potential to use as a biodegradable active edible film for food packaging.