This study investigates whether laminarin (β1-3,β1-6-glucan), a polysaccharide from seaweed, exhibits beneficial properties for human health by analysing its effects on intestinal parameters. Anaerobic batch culture fermenters were used for the screening of the in vitro utilization of laminarin by the human gut microflora through the monitoring of biochemical and microbiological parameters. Additionally, the influence of laminarin ingestion on the composition of intestinal mucus (neutral mucins, sialomucins and sulphomucins) was studied in rats. Laminarin was almost totally (more than 90% used) fermented after 24 h of incubation with human intestinal bacteria. It was not selectively used by bifidobacteria and lactobacilli, but increased the production of propionate and butyrate. Variations of mucus composition were observed in jejunum, ileum, caecum and colon, both in lumen content and in intestinal wall, of rats after ingestion of this polysaccharide. Due to its effects on mucus composition, laminarin could influence the adherence and the translocation of bacteria across the epithelial wall. In conclusion, laminarin seems to be a modulator of the intestinal metabolism by its effects on mucus composition, intestinal pH and short chain fatty acid (SCFA) production, especially butyrate.

Dietary fibres consist of edible plant polysaccharides that are resistant to digestion and absorption in the human small intestine but undergo complete or partial fermentation in the colon. Seaweeds, notably Laminaria spp, are particularly rich in polysaccharides resistant to hydrolysis in the upper gastrointestinal tract and are, in consequence, considered as dietary fibres. Most of the carbohydrates from Laminaria spp are thought to be indigestible by humans. The main storage polysaccharide of these algae is laminarin, a β-polymer of glucose. The aims of this work were, on the one hand, to compare various methods of extraction of laminarin by partial characterisation of the product obtained and, on the other hand, to study the fate of this polysaccharide and its effects in the gastrointestinal tract in order to determine its potential as a dietary fibre in human nutrition. Among four methods tested to extract laminarin, the best appeared to be a hot HCl-based method. Human digestive enzymes did not hydrolyse laminarin, so this polysaccharide can be considered as a dietary fibre. After ingestion by rats, this polysaccharide was not found in faeces of these animals. It did not increase the intestinal transit and stool output in vivo, but it increased the contractile response of the stomach to acetylcholine in vitro.

Background: The absorptive and goblet cells are the main cellular types encountered in the intestine epithelium. The cell lineage Caco-2 is a model commonly used to reproduce the features of the bowel epithelium. However, there is a strong debate regarding the value of Caco-2 cell culture to mimick in vivo situation. Indeed, some authors report in Caco-2 a low paracellular permeability and an ease of access of highly diffusible small molecules to the microvilli, due to an almost complete lack of mucus. The HT29-5M21 intestinal cell lineage is a mucin-secreting cellular population. A co-culture system carried out in a serum-free medium and comprising both Caco-2 and HT29-5M21 cells was developed. The systematic use of a co-culture system requires the characterization of the monolayer under a given experimental procedure.

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