Flexible Edible Materials from Extrusion-Plasticized Modified Cassava Starches with Maltol and Ethyl Maltol: Molecular Interactions, Mechanical Properties, and Antioxidant and Antimicrobial Activities

This study systematically investigated how cassava starch modification chemistry and hydroxypropyl substitution level influence the structure and functional performance of extrusion-plasticized edible materials containing maltol or ethyl maltol. Native starch, acetylated starch, octenyl succinate-modified starch, and hydroxypropylated starches with low, medium, and high substitution levels were incorporated with 3% maltol or ethyl maltol and processed by twin-screw extrusion. The resulting materials were characterized for microstructure, molecular environment, crystalline organization, thermal behavior, mechanical properties, antioxidant activity, and antimicrobial performance. FTIR and NMR analyses showed changes in the molecular environment after incorporation of the maltol derivatives, while XRD revealed formulation-dependent differences in structural ordering. Mechanical responses were strongly matrix-dependent, with tensile strength, elongation at break, and Young’s modulus reaching up to 3.56 MPa, 552%, and 108 MPa, respectively. DPPH radical-scavenging activity increased with extraction time and reached approximately 80–82% after 5 h in the most active formulations. Antibacterial activity was selective, with the largest inhibition zone against Bacillus subtilis reaching 3.53 mm, whereas no inhibition zones were detected against Staphylococcus aureus or Escherichia coli. Antifungal activity was more pronounced, with maximum inhibition zones of 7.39 mm against Aspergillus niger and 0.55 mm against Penicillium sp.; no distinct inhibition zone was observed against Rhizopus sp., although delayed sporulation was observed in some maltol-containing samples. These findings demonstrate that starch modification chemistry and substitution level govern the balance among structural organization, mechanical behavior, antioxidant activity, and selective antimicrobial performance of extrusion-plasticized cassava starch matrices containing maltol derivatives.