Scalable Valorization of Sargassum thunbergii Biomass to Produce Bioactive Fucoidan with Immunomodulatory and Gut Health Applications.

Marine macroalgae such as Sargassum thunbergii (ST) represent an abundant but underutilized biomass resource with strong potential for valorization into high-value bioactive compounds. In this study, a scalable and environmentally friendly extraction process was developed to obtain fucoidan from unused S. thunbergii . The process involved 1% acetic acid soaking, hot water extraction, 5% CaCl₂ treatment at pH 11, ethanol precipitation (1:3 v/v) at pH 5, and freeze drying. The resulting fucoidan (STF) exhibited a high sulfate (~ 16%) and fucose (~ 19–20%) content, while retaining essential minerals and meeting safety standards (total arsenic: 3.0 mg/kg; inorganic arsenic: 0.79 mg/kg). In vitro analyses demonstrated that STF enhances nitric oxide production, activates the NF-κB signaling pathway, and suppresses Th17 cell polarization, indicating strong immunomodulatory potential. In vivo, STF and chitooligosaccharides (COS) were evaluated using a DSS-induced zebrafish intestinal inflammation model. STF and COS treatment significantly downregulated pro-inflammatory IL-1β expression, thereby aiding in gut microbiota balance, characterized by increased microbial diversity, enrichment of beneficial taxa such as Lactobacillus , and reduced dominance of Cetobacterium . These findings highlight the feasibility of valorizing S. thunbergii biomass into bioactive fucoidan with potential applications in functional foods, dietary supplements, and nutraceuticals promoting intestinal and immune health.