It is a challenge to degrade sulfated polysaccharides without stripping sulfate groups. In the present study, a photocatalytic method was applied to degrade fucoidan, a sulfated polysaccharide from brown algae. The degradation with varying addition amounts of H₂O₂ and TiO₂ were monitored by high performance gel permeation chromatography (HPGPC) and thin layer chromatography (TLC), and fucoidan was efficiently degraded with 5% TiO₂ and 0.95% H₂O₂. A comparison of the chemical compositions of 2 products obtained after 0.5 h and 3 h illumination, DF-0.5 (average Mw 90 kDa) and DF-3 (average Mw 3 kDa), respectively, with those of fucoidan indicates the photocatalytic degradation did not strip the sulfate groups, but reduced the galactose/fucose ratio. Moreover, 12 oligosaccharides in DF-3 were identified by HPLC-ESI-MSⁿ and 10 of them were sulfated. In addition, DF-0.5 showed anticoagulant activity as strong as fucoidan while DF-3 could specifically prolong the activated partial thromboplastin time. All samples exerted inhibition effects on the intrinsic pathway FXII in a dose-dependent manner. Thus, photocatalytic degradation demonstrated the potential to prepare sulfated low-molecular-weight fucoidan with anticoagulant activity.

Obesity is a major global health concern associated with various metabolic disorders. Fucoidan, a seaweed-derived sulfated polysaccharide, has shown potential in alleviating obesity through modulation of gut microbiota. However, comparative effects of native and depolymerized fucoidan (Dfuc) on HFD-induced obesity and gut microbiota dysbiosis remain unclear. In this study, we compared the anti-obesity effects of fucoidan and Dfuc and evaluated their regulatory effects on gut microbiota and microbial metabolites in HFD-fed mice. Results showed that fucoidan and Dfuc reduced body weight gain, fat accumulation and hepatic lipid abnormalities. They also alleviated liver injury and oxidative stress and inflammation in hepatic and colonic tissues, with Dfuc significantly improving parameters such as serum AST, hepatic MDA, SOD activity, and TNF-α expression compared to the HF group. Furthermore, gut microbiota analysis showed that both fucoidan and Dfuc treatments enriched Alloprevotella and Allobaculum, while fucoidan increased Akkermansia and Blautia, and Dfuc promoted Bifidobacterium and Romboutsia. Moreover, metabolite analysis showed that Dfuc significantly increased fecal acetate and propionate concentrations, and induced more pronounced changes in fecal metabolites related to amino acid, carbohydrate, and bile acid metabolism. These findings suggest that Dfuc holds potential as a functional food ingredient for alleviating HFD-induced obesity and gut microbiota dysbiosis.