Mechanisms of <i>Laminaria japonica</i> Polysaccharide Digestion and Absorption: Structure, In Vivo Fluorescence Imaging, and Gut Microbiota

This study clarified the structure and digestive properties of the <i>Laminaria japonica</i> polysaccharide (LJP). It was demonstrated that LJP belongs to a heteropolysaccharide composed of mannuronic acid, fucose, galactose, glucuronic acid, mannose, xylose, glucose, and guluronic acid in the proportion of 34.56%: 30.55%: 10.63%: 7.52%: 6.66%: 3.74%: 3.62%: 2.72%, with a backbone chain composed of →4)-β-d-ManA-(1→, →3)-α-l-Fuc<i>p</i>-(1→, →4)-α-GulA-(1→, →3,4)-α-GlcA-(1→, and →4)-β-d-GlcA-(1→. In vivo fluorescence imaging indicated that LJP was mainly distributed in the stomach and intestinal segments of mice, and the fluorescence signal gradually disappeared after 12 h of digestion. In addition, LJP had no effect on the phenotype and general health of mice while promoting the proliferation of the beneficial bacteria <i>Rikenella</i>, <i>Rikenellaceae_RC9_gut_group</i>. Notably, 100 mg/kg LJP significantly increased the levels of acetic and butyric acid in the mice feces, which were 1.51 and 2.65 folds higher than the controls, respectively. Our study illuminated the absorption and distribution mechanism of LJP, providing a scientific reference for revealing LJP as a potential prebiotic.