Oligosaccharides possess characteristics such as low molecular weight, good solubility, and high bioavailability, which make them better absorbed than fucoidan. This study hypothesizes that fucoidan oligosaccharides can be absorbed by intestinal epithelial cells and quickly enter the bloodstream, with a rapid absorption rate. In this study, fucoidan oligosaccharides were obtained through acid degradation and Bio Gel column separation. By analyzing the chemical composition and molecular weight, oligosaccharides with smaller molecular weights and simpler monosaccharide compositions were selected for further research. A cell model and pharmacokinetic studies in mice were established to analyze the absorption patterns of the oligosaccharides. The results showed that after acid degradation and column separation, high-molecular-weight oligosaccharides SPF1 with a molecular weight range of 1.63 × 10⁴ to 2.14 × 10⁵ Da and the low-molecular-weight oligosaccharides SPF2 with a molecular weight range of 244.22 to 1545.36 Da were obtained. In cell transport and uptake experiments, the transport of SPF1 and SPF2 was positively correlated with time and negatively correlated with concentration. The transport rates of SPF1 and SPF2 ranged from 20% to 70%, with P_app values greater than 1 × 10⁻⁵ cm/s. In the pharmacokinetics study, the blood concentration of the oligosaccharides in mice was simulated and analyzed using DAS 2.0, which indicated that the fucoidan oligosaccharides exhibited good absorption characteristics in vivo and in vitro. Therefore, fucoidan oligosaccharides with smaller molecular weights are more easily absorbed, which provides a theoretical basis for the application of fucoidan oligosaccharides.

This study investigated how different extraction parts of raw materials and different flocculation methods affect the extraction yield, structure, and properties of sodium alginate. The aim was to improve the quality of sodium alginate and provide theoretical guidance for upstream enterprises. In this study, Lessonia nigrescens (LN) was used as a raw material. The alkali treatment conditions were optimized. The optimal extraction conditions were determined to be a 2% sodium carbonate concentration, a duration of 4 h, a material-to-liquid ratio of 1:40, and a temperature of 60 °C, achieving an extraction yield of 43.03%. LN was categorized into blades, stipes, holdfasts, and whole seaweed for comparative analysis, and sodium alginate was flocculated using the acid, calcium, and ethanol methods. Structural and physicochemical analyses showed that the mannuronic acid/guluronic acid (M/G) ratios of the twelve sodium alginate samples ranged from 5.73 to 8.76. The LN part had a greater influence on the M/G ratio than the flocculation method. The relative molecular weight (2343–3074 kDa) and viscosity (170–331 mPa·s) exhibited consistent trends. For the same part, the effect of the flocculation method on the molecular weight followed the order ethanol > acid > calcium. The physicochemical properties of the extracted sodium alginate met the requirements specified in the physicochemical index standard GB 1886.243-2016 of China.

Ulcerative colitis (UC) is a form of inflammatory bowel disease (IBD), which is marked by severe abdominal pain, weight loss, perianal bleeding, and diarrhea. This study successfully isolated and purified four low-molecular-weight fucoidan oligosaccharides through acid hydrolysis and Bio Gel P10 gel filtration. The molecular weights were 2.9 × 10⁴–1.36 × 10⁵ Da, 182–1012 Da, 161–939 Da and 161–939 Da, respectively. A mouse model of colitis was induced using Dextran Sulfate Sodium (DSS). The results indicated that fucoidan and fucoidan oligosaccharides could ameliorate murine ulcerative colitis, with the oligosaccharides (200 mg/kg/d) demonstrating superior therapeutic effects. This superiority was likely attributed to the lower molecular weight and higher content of total sugars and fucose. The primary mechanisms involved the modulation of gene and protein expression levels associated with the Toll-like receptor 4, Myeloid differentiation primary response 88, nuclear factor kappa-light-chain-enhancer of activated B cells, p65, and Inhibitor of kappa light polypeptide gene enhancer in B cells, alpha (TLR4, MYD88, NF-κB p65, and IκB-α) signaling pathways, which reduce the production of inflammatory cytokines such as tumor necrosis factor-alpha, Interleukin-1 beta and Interleukin-6 (TNF-α, IL-1β, and IL-6). Additionally, these oligosaccharides alleviated oxidative stress, enhanced the levels of intestinal barrier proteins (Claudin family member 4 and Zonula occludens protein 1), regulated the abundance and diversity of the gut microbiota, and increased the levels of short-chain fatty acids (SCFAs) in the intestine. It is worth emphasizing that this study can only demonstrate that fucoidan oligosaccharides have a mitigating effect on intestinal inflammation in mice. Further research is needed in the future to investigate the structure–activity relationship of fucoidan oligosaccharides and their impact on human intestinal microbiota, in order to further elucidate their anti-inflammatory mechanisms.