Rheological characteristics of fucoidan-galactomannan mixtures

We investigated the steady and dynamic shear rheological properties of fucoidan-galactomannan (GM) with different mannose-to-galactose (M/G) ratios to confirm the intermolecular interactions between fucoidan and GMs [locust bean gum (LBG), tara gum (TG), and guar gum (GG)]. All fucoidan-GM mixtures exhibited pseudoplastic behavior, and the apparent viscosity at 50 s⁻¹ (η_a,50) values increased in a fucoidan concentration-dependent manner. Similarly, the dynamic moduli of mixtures exhibited an increasing tendency with higher fucoidan concentrations. A pronounced decrease in the activation energy of viscosity was observed in the fucoidan-LBG mixture as the fucoidan concentration increased. Crossover was noted in plots of dynamic moduli vs. frequency, and the crossover point shifted toward low frequency with adding more fucoidan. The relative magnitudes of η_a,50, dynamic moduli, and intrinsic viscosity of mixtures increased as fucoidan concentration increased, with the fucoidan-LBG mixture exhibiting the highest relative values, followed by fucoidan-TG and -GG mixtures. The intermolecular energy between fucoidan and GMs, determined by molecular docking, exhibited the following order: GG (− 20.8 kJ·mol⁻¹) > TG (− 22.2 kJ·mol⁻¹) > LBG (− 31.0 kJ·mol⁻¹). These results demonstrate that there are intermolecular interactions between fucoidan and GMs, and fucoidan tends to form more and stronger interactions with GMs having a higher M/G ratio.