Effect of Fucoidan on Rheological and Tribological Properties of Milk Protein Isolate

This study investigated the effects of fucoidan (1–3 wt%) on the rheological and tribological properties of milk protein isolate (MPI, 15 wt%). With increasing fucoidan concentration, particle sizes of MPI–fucoidan mixtures significantly increased, and their ζ-potentials gradually decreased. Fourier transform infrared spectroscopy confirmed the presence of intermolecular interactions between MPI and fucoidan, while scanning electron microscopy revealed that these interactions promoted the formation of a more uniform, compact, and robust three-dimensional network structure. The MPI-fucoidan mixtures exhibited significantly lower flow behavior indices (0.44–0.48) and higher consistency indices (7.24–10.1 Pa∙sⁿ) and apparent viscosity at 100 s⁻¹ (0.67–0.75 Pa∙s) compared to that without fucoidan (0.52, 1.19 Pa∙sⁿ, and 0.21 Pa∙s, respectively). Viscoelastic properties also significantly improved with higher fucoidan concentrations, with the elastic modulus showing a more pronounced increase than the viscous modulus. While MPI alone exhibited time-independent flow behavior, MPI-fucoidan mixtures displayed thixotropic behavior. All samples showed friction curves with five distinct regimes, and both maximum and minimum friction coefficients decreased as fucoidan concentration increased, indicating improved lubrication. These findings suggest that fucoidan can enhance the tribo-rheological performance of MPI, offering potential applications in food formulation.