Green Modifiers for Sustainable Kuzu Starch-Based Films: Tailoring Functional Properties

Studies have shown that the use of readily available and easily prepared modifiers can control the specific properties of the starch material, targeting those that are most beneficial for specific applications. Starch is one of the materials poised to replace traditional polymers in food packaging and wound dressings. However, its functional properties, including barrier properties, antibacterial and mechanical properties, need to be improved. Films made of kuzu starch cross-linked with citric acid and plasticised with glycerol were modified with various modifiers: Kalanchoe pinnata extract, silver nanoparticles in this extract, an extract additionally stabilised with a biopreservative, and chitosan. The effect of these modifiers on the chemical structure and morphology of the starch films, as well as on their barrier properties, thermal, mechanical, and bacteriostatic properties, was determined. Only films containing silver nanoparticles produced clear inhibition zones against Staphylococcus aureus and Escherichia coli. Chitosan-containing films exhibited weak antibacterial activity, while no measurable inhibition zones were observed for unmodified starch films or films containing only Kalanchoe pinnata extract. No viable yeasts or moulds were detected on the film surfaces during the 14-day storage period under the conditions of the study. The starch film with chitosan had the highest tensile strength, while film with the Kalanchoe pinnata extract had the highest elongation. The film made of starch with Kalanchoe pinnata extract had the highest water vapour transmission rate and the lowest contact angle, while the film made of starch with chitosan had the highest barrier properties.