Study on the mechanical properties, shape memory behavior, microstructure, and deformation mechanism of starch–chitosan shape memory food emulsion gels: Salt-responsive basis

To overcome the limitations of deformable foods with a single deformation mode and an uncontrollable final shape, this study constructed a salt-responsive shape memory emulsion gel (SMEG) using starch and chitosan (CS), introducing programmable deformation behavior into deformable food systems. The results indicate that at a CS concentration of 2.0% (m/v, CS (2.0)), the gel exhibits a dense and uniform three-dimensional network structure. It can be bent into a spiral shape and fully recovers its original shape after the external force is removed, without wrinkles or cracks, demonstrating good flexibility. This provides the essential physical foundation for its shape memory behavior. CS (2.0) can efficiently fix temporary shapes in NaCl solution (approximately 100% shape memory rate) and fully recover to its original shape in deionized water (approximately 100% recovery rate), while allowing autonomous definition of multiple temporary shapes. Systematic studies using rheology, microstructural observations (SEM, CLSM), and characterization of intermolecular interactions (FTIR) indicate that during the shape fixing stage, enhanced hydrogen bonding densify the polymer network; during the recovery stage, deionized water removes salt ions and disrupts temporary hydrogen bonds, driving network expansion and shape recovery. The reversible phase of CS (2.0) corresponds to a temporary physical crosslinking state formed between CS and NaCl, fixing the temporary shape, while hydrogen bonds act as the main noncovalent interactions driving shape memory recovery. This study provides new theoretical guidance for the design of food hydrogels with controllable shape memory properties.