Preparation and characterization of kodo millet starch/gum tragacanth/ copper oxide nanoparticles-based antimicrobial food packaging films

This work developed antimicrobial bio-nanocomposite films using Kodo millet starch (KMS) and gum tragacanth (GT) with varying concentrations (1, 2, and 3 % w/w) of copper oxide nanoparticles (CuO NPs) via solution casting technique. Incorporating CuO NPs decreases the viscoelastic attributes of the KMS/GT film-forming dispersions, indicating the disentanglement of polymer chains. Adding hydrophobic CuO NPs significantly reduces the free hydroxyl groups in the KMS/GT matrix and decreases the water solubility by increasing surface hydrophobicity (up to similar to 92 degrees). The KMS/GT/CuO NP nanocomposite films showed strong UV barrier properties due to the UV-light absorbing capacity of CuO NPs. The surface micrographs displayed that the increase in CuO NPs concentrations increases the surface roughness due to the agglomeration of NPs. The XRD results confirm the presence of CuO NPs in the film matrix and the increasing crystallinity in the nanocomposite films. The loading of 3 % CuO NPs improved the tensile strength (from 9.31 +/- 2.24 MPa to 13.21 +/- 2.98 MPa) and Young's modulus (from 12.21 +/- 2.65 MPa to 17.06 +/- 2.69 MPa), due to the reinforcement ability of CuO NPs. In addition, the increase in CuO NPs concentrations enhances the water vapor barrier properties (up to 88 %) of the KMS/GT films. Furthermore, incorporating CuO NPs into KMS/GT films imparted strong antimicrobial activity against Bacillus cereus and Escherichia coli microorganisms. The prepared KMS/GT/CuO NPs films could be a sustainable antimicrobial packaging material for food packaging applications.