Low temperature preparation of high-performance citric acid crosslinked starch gels with adjustable properties based on cationic esterification synergistic crosslinking

Citric acid (CA) is a commonly used crosslinking agent for good-grade starch gels, but its high crosslinking temperature limits its application. Recent attempts to prepare CA-crosslinked modified starch gels (SC) at low temperatures have resulted in low crosslinking degrees that do not meet application requirements. This study presents a new method for stable preparation of high-strength Fe3+-CA synergistic crosslinked starch gels at low temperatures (90 °C), carried out in a stable and controlled multi-physical field high-shear reaction environment. The enhancement effect of synergistic crosslinking reaction on starch gel properties was quantitatively characterized by linear and nonlinear rheological properties. The results showed that the elastic modulus of synergistically crosslinked modified SC-0.6Fe3+ (G' = 1082.71 ± 21.50) at 0.1% strain was significantly increased by 491.57% compared to the elastic modulus of SC (G' = 183.04 ± 13.32) without synergistic crosslinking modification. SC-0.6Fe3+ demonstrated the largest elastic Lissajous ring area, indicating stronger resistance to deformation in the synergistic crosslinked gel system. Additionally, adjusting the cation concentration allowed for flexible modulation of the rheological properties of starch gels. SEM and N2 adsorption data revealed that SC-0.6Fe3+ had a denser honeycomb porous structure and a smaller pore size distribution. FTIR, XRD, DSC, and TGA results suggested that the synergistic crosslinking enhancement effect might be achieved through electrostatic attraction, hydrogen bonding, ionic dipole interactions, and ester bonding. Our work provides an effective strategy for batch preparation of adjustable high-performance food-grade crosslinked starch gels in low-temperature environments.