Synergistic effect of dual mechanical-chemical modification on κ-carrageenan matrix: enhanced esterification efficiency and physicochemical performance

κ-carrageenan (KC) is a sulfated linear polysaccharide derived from red algae whose functional properties may be limited by insufficient water retention and freeze-thaw stability. This study employed a dual modification strategy combining mechanical activation and glutaric anhydride esterification to address these limitations. The results showed that this approach significantly improved the esterification efficiency of KC and enhanced the freeze-thaw stability of its gels and emulsion gels. As characterized by scanning electron microscopy and infrared spectroscopy of the particles, it was found that the dual modification led to dissociated original morphology and increased surface roughness of KC particles, which was beneficial to the diffusion of GA molecules and water molecules into the particles, and ultimately led to an increase in the esterification degree by 20.9 %. Meanwhile, as the GA groups were introduced, they enhanced the intermolecular electrostatic repulsion and spatial site resistance effects, significantly improving KC water-holding capacity. SEM and LF-NMR of the gel further confirmed that the dual modification could effectively alleviate the irreversible destruction of the gel network during freezing-thawing, resulting in a lower freeze-thaw dehydration rate and a noticeable improvement in the emulsion gel's freeze-thaw stability. This study provides an innovative modification strategy for improving KC's functional properties and expanding its industrial applications.