In vitro digestion and fermentation of three polysaccharide fractions from Laminaria japonica and their impact on lipid metabolism-associated human gut microbiota.

Our previous study has proved that the three polysaccharide fractions from L. japonica (LP-A4, LP-A6, and LP-A8) had significantly different structure characterization. Herein, we conducted in vitro simulated digestion and fermentation to study the digestive mechanism of LP-As. The results of gastrointestinal digestion indicated that LP-A6 and LP-A8 would be easier to trap the enzyme molecules for their denser interconnected macromolecule network compared with LP-A4. Fermentation of LP-As by human gut microbiota, especially for LP-A8, generated a large amount of short-chain fatty acids (SCFAs), which could upregulate the abundance of Firmicutes (Lachnoclostridium and Eubacterium). The high content of sulfate and highly branched sugar residue of LP-A8 might help it be easily used by Firmicutes in gut microbiota of hyperlipidemic patients. Functional analysis revealed that the increased metabolic activities of glycerophospholipid metabolism, ether lipid metabolism, and fatty acid metabolism induced by LP-A8 treatment were closely associated with metabolic syndromes and hyperlipidemia.