Effect of alkali pretreatment on paramylon hydrogel: Structure, rheology, and formation mechanism

Paramylon hydrogels were prepared by pretreating β-1,3-glucan in NaOH or KOH (≥0.5 M) to disrupt its triple-helix structure, followed by HCl neutralization. The influence of Na⁺ versus K⁺ on hydrogel properties was examined. Gelation was shown to depend on hydrogen bonding, hydrophobic interactions, and electrostatic shielding via urea, SDS, and salt experiments. Enhanced hydrogen bonding manifested as broader FTIR hydroxyl peaks, higher DSC denaturation temperatures, and greater water retention capacity. The 0.9 M KOH-pretreated sample showed 1.25 times higher water retention (88.54%) than its NaOH counterpart, with a more compact microstructure. Enhanced hydrophobic interactions were evidenced by C6 signal shifts in ssNMR and aggregated fiber bundles in AFM. Rheologically, KOH-based hydrogels exhibited a 1.85-fold higher storage modulus (G′), further increased by salt addition, confirming electrostatic shielding. Their superior toughness was reflected in TPA, where KOH-pretreated hydrogels showed greater cohesiveness and a 5.5-fold higher chewiness than NaOH-based counterparts. The large ionic radius and thin hydration layer of K + enabled a "jigsaw puzzle" mechanism, yielding superior paramylon hydrogels under KOH pretreatment. By regulating alkali concentration and cation type, the structure and function of paramylon hydrogels were tailored, providing theoretical support for their applications in food and other fields.