Whey Protein Concentrate/Zinc Oxide bionanocomposites for antimicrobial applications

Developing advanced antimicrobial materials is a key necessity in ensuring proper control and management of microbial infections. New therapeutic strategies are required to overcome the onset of antimicrobial resistance (AMR) and more biocompatible compounds shall replace the currently used petroleum-derived plastics in the fabrication of antimicrobial devices. The present work offers a preliminary investigation of whey protein concentrate (WPC)/zinc oxide (ZnO) composites to combine the biocompatibility of WPC with the antimicrobial properties of zinc oxide. Two types of composites were prepared with a simple, crosslinker-free, solvent casting method, by varying the content of two different samples of ZnO, i.e. a commercial zinc oxide powder, characterized by well-defined micrometric crystals, and a nanostructured ZnO, synthesised by wet chemical precipitation and characterized by nanometric quasi-spherical particles. Composites were characterised with Field Emission Scanning Electron Microscopy (FE-SEM), UV-vis spectrophotometry and Fourier Transform Infrared Spectroscopy (FTIR) techniques. Functional properties were assessed with swelling and solubility tests and with moisture content measurements. Antimicrobial tests against S. epidermidis (Gram+) and E. coli (Gram-) were performed to assess the performances of the composites and of the two ZnO samples. A ZnO dose-dependent effect was observed and significant improvements in antimicrobial properties were obtained when the metal oxide was present in its nanostructured form. This improvement can be attributed to the smaller size of the nanoparticles and the higher surface area of the material. These early findings suggest that these bionanocomposites could represent a promising technology in wound healing or food packaging applications.