Effect of Simulated Salivary Fluid on Tribo-Rheological Properties of Fucoidan-Guar Gum Mixtures and their Anti-Inflammatory Activity after in Vitro Digestion

Abstract

Fucoidan holds promise for use in functional beverages due to its various bioactivities, including anti-inflammatory activity, particularly for elderly individuals. To ensure safe consumption by those with swallowing difficulties, these beverages need to be thickened using agents such as guar gum (GG) at high concentrations (21.0%). Therefore, this study investigated the influence of saliva on the tribo-rheological properties of 1.0% GG-based fucoidan mixtures, which are closely related to mouthfeel during the oral processing. Additionally, the post-digestive anti-inflamma-tory activity of fucoidan-GG mixtures was evaluated using the INFOGEST digestion model. All mixtures exhibited pseudoplastic flow behavior, and their apparent viscosity and viscoelastic moduli tended to increase with increasing fucoidan content. The presence of simulated salivary fluid (SSF) reduced shear-thinning behavior and overall rheo-logical characteristics. Specifically, the SSF-mixed samples exhibited shorter relaxation times and more pronounced changes in viscoelastic moduli as a function of the fucoidan-to-GG ratio compared to their original counterparts, sug-gesting alterations in the nature of intermolecular interactions between the two biopolymers. These changes altered the tribological behavior of the mixtures. A decreasing trend in the friction coefficient was observed with increasing fucoidan content. Additionally, higher fucoidan content led to a delayed transition from the boundary to mixed lubri-cation regime in both original and SSF-mixed samples, with a more pronounced delay observed in the latter. After digestion, fucoidan-rich mixtures ([fucoidan] >= [GG]) significantly suppressed tumor necrosis factor-a production in lipopolysaccharide-stimulated RAW264.7 cells. These findings can provide insights into the design of dysphagia-friendly functional beverages containing fucoidan.