Microstructural insights and mechanical properties of physically crosslinked starch hydrogels via two-way amylose regulation.
Physical starch hydrogels have attracted significant attention due to their biodegradability and biocompatibility as clean-label hydrogels. In this work, we investigate the combined effect of maize starch amylose content and concentration on the formation of physically crosslinked low- and high-amylose hydrogels, prepared through a three-step physical process (swelling, gelatinization, retrogradation). Rheological characterization, including steady-state and dynamic measurements, was used to evaluate the texture profile analysis (TPA), hardness, fluid release and consistency coefficient (K). High-amylose maize hydrogels display 5-7 fold increase in hardness and 5-16 fold decrease in cohesiveness, with the dynamic mechanical loss tangent (tan δ) value being 0.12 for the hardest high-amylose studied sample. The microstructure and the correlation to the mechanical properties, retrogradation and syneresis were investigated by complementary scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). The role of hydrogen bonding between water molecules and polysaccharide chains with different order of organization, is highlighted. Our results provide insight into starch re-organization, including the formation of single-stranded amylose helices (V-amylose) within the crystalline and amorphous regions. Overall, we demonstrate that the mechanical properties and syneresis behavior of starch-based hydrogels could be effectively tailored by the proposed two-way amylose regulation, offering a promising strategy for developing bioinks for 3D printing in functional food applications.