Funoran is a sulfated red algal polysaccharide belonging to the broader class of agarans. Although it shares certain structural features with agarose and porphyran, funoran remains comparatively under-characterized, particularly regarding its cation-mediated structural and functional properties. In this study, funoran fractions extracted from several Gloiopeltis species were systematically analyzed to elucidate their structural features and physicochemical behavior as hydrocolloids. The polymers were characterized using HPLC, FTIR, ¹H NMR spectroscopy, rheology, and wide-angle X-ray scattering (WAXS).

¹H NMR analysis confirmed the primary repeating unit of funoran as G6S – LA (β-d-galactose-6-sulfate–3,6-anhydro-α-l-galactose). WAXS revealed that the addition of only 20 mM BaCl₂ induced a distinct structural transformation, evidenced by the splitting of diffraction peaks into multiple reflections. This peak separation indicates increased chain ordering and tighter molecular packing, suggesting a strong and specific interaction between Ba²⁺ ions and funoran chains.

Ion-mediated changes were also evident in rheological measurements. At 300 mM BaCl₂, the storage modulus (G′) increased by more than an order of magnitude compared with the control (without Ba²⁺), reflecting a substantial enhancement in gel strength and network cohesion. This dramatic rise in viscoelasticity is consistent with the formation of strong intermolecular cross-links and a denser polymer network mediated by divalent cations.

Overall, these findings provide important new insights into the structure–function relationships of funorans and demonstrate that divalent cation modulation—particularly through Ba²⁺—offers a powerful strategy for tailoring the rheological and structural properties of sulfated agarans for cosmetic, biomedical, and other biotechnological hydrocolloid applications