Preparation and characterization of casein films loaded with silver nanoparticles for food packaging applications

Current trends in food packaging emphasize the use of biodegradable, renewable materials instead of fossil-derived polymer materials. In this study, edible films were prepared from both pure casein and casein extracted from skim milk powder. Potassium sorbate was incorporated as a preservative in the film-forming solutions. The study was conducted in two sequential stages. In the first stage, various concentrations of glycerol (1%, 2%, and 3% v/v) were tested to identify the optimal level of plasticizer based on the physical and mechanical properties of the films. Once the optimal glycerol concentration was determined, it was kept constant for the preparation of films reinforced with silver nanoparticles (AgNPs). Subsequently, AgNPs were incorporated at different concentrations (20, 30, 40, and 50 ppm), and their effects on the physical, mechanical, and antimicrobial properties of the films were evaluated. The results showed that glycerol improved elongation at break but reduced tensile strength. The optimum concentration (2% v/v) provided a balance between tensile strength (5.4 MPa) and elongation at break (26%) for films prepared from extracted casein. A decrease in water vapour permeability (WVP) was observed with increasing AgNPs concentration, where WVP decreased by 20.12% and 23.76% at 50 ppm for pure and extracted casein films, respectively. Mechanical properties were also enhanced, with tensile strength increasing by 63.41% and 35.18% for extracted and pure casein films, respectively. Furthermore, AgNPs significantly reduced the total bacterial count by 90% and 70% for extracted and pure casein films, respectively, as well as yeast and mold counts.