Conformational and rheological behavior of kappa carrageenan in glycerol: Effects of sodium salts and preparation temperature

Kappa carrageenan (KC), a sulfated polysaccharide derived from red seaweed, exhibits distinct gelation properties that are influenced by ionic strength and thermal conditions. While its behavior in aqueous media is well-established, understanding KC's gelation mechanisms in non-aqueous solvents (like glycerol) remains limited. This study investigates the conformational and rheological properties of kappa carrageenan in glycerol, focusing on the effects of sodium salts (NaCl, NaH₂PO₄, Na₃PO₄) at varying concentrations and preparation temperatures (60 °C and 80 °C). Rheological measurements reveal distinct viscosity trends influenced by salt type and temperature, highlighting the interplay between ionic interactions and KC's conformational transitions. Phosphate salts significantly enhance network elasticity and stability, especially at intermediate concentrations, whereas NaCl induces weaker, viscosity-dominated structures. Atomic force microscopy imaging provides complementary nanoscale insights, showcasing salt-specific structural transitions from looped to branched networks, alongside a temperature-dependent helix-to-coil transformation. These results illustrate how the precisely tuning ionic conditions and the preparation temperatures in glycerol media can effectively modulate KC's structure and viscoelastic properties. This deeper understanding facilitates targeted design and optimization of carrageenan-based materials across food, pharmaceutical, cosmetic, and biotechnological applications.