Insoluble Retrogradation-Resistant Starch-Chitosan Foams

Insoluble starch-chitosan foams were produced through a novel plasticization process that integrates glycerol via a post-expansion soaking and freeze-drying process. Starch foams incorporating 4% and 8% chitosan were first expanded and cross-linked using microwave heating, then soaked in a 7.5% glycerol solution, frozen, and freeze-dried to retain glycerol within the foam matrix. This process uniquely preserves the position of the glycerol in the foam by sublimating water during freeze-drying, allowing for internal plasticization without structural collapse. The resulting foams showed up to a 43% reduction in compressive modulus, yielding mechanically soft yet stable structures. Rheological characterization revealed that chitosan-starch polyelectrolyte complexation helped reduce retrogradation with the presence of glycerol. Increasing chitosan content enhanced foam integrity, while swelling behavior confirmed that both chitosan and glycerol concentrations influenced solution uptake. This study demonstrates a promising method for producing soft, insoluble, stable and retrogradation-resistant starch-based foams for a wide variety of diverse applications.