Gut-protective efficacy of red algal galactans: The role of structure and molecular weight.

Linking structure, rheology, and bioactivity, this study demonstrates how red algal galactans can be tailored as functional food ingredients with gut-protective potential. Funoran and furcellaran were isolated from Gloiopeltis furcata and Furcellaria lumbricalis, respectively, and characterized using chromatographic and NMR spectroscopic techniques. Funoran was identified as a highly sulfated, methoxylated agaran (22.7% sulfate), whereas furcellaran exhibited a hybrid κ-/β-carrageenan structure (17.4% sulfate). High molecular weights (3955 and 2966 kDa) were observed and reduced via controlled autohydrolysis without sulfate loss. Structural variations governed rheological behavior, with furcellaran showing ion-dependent gelation and funoran forming weaker networks. Both native and depolymerized galactans were non-cytotoxic to Caco-2 cells, maintained tight junction integrity, and reduced oxidative stress. In a DSS-induced colitis model, treatments alleviated clinical symptoms, decreased pro-inflammatory cytokines and MPO activity, and restored barrier-related proteins. Metagenomic analysis revealed partial correction of dysbiosis, including enrichment of short-chain fatty acid producing taxa, particularly in depolymerized funoran. Overall, structural features and molecular weight critically determine both rheological and biological functions. Depolymerization enhances fermentability while preserving bioactivity, highlighting red-algal galactans as promising multifunctional hydrocolloids for food and gut health applications.