Abstract
BackgroundBrown seaweeds are known to be a rich source of fiber with the presence of several non-digestible polysaccharides including laminarin, fucoidan and alginate. These individual polysaccharides have previously been shown to favorably alter the gut microbiota composition and activity albeit the effect of the collective brown seaweed fiber component on the microbiota remains to be determined.MethodsThis study investigated the effect of a crude polysaccharide-rich extract obtained from Laminaria digitata (CE) and a depolymerized CE extract (DE) on the gut microbiota composition and metabolism using an in vitro fecal batch culture model though metagenomic compositional analysis using 16S rRNA FLX amplicon pyrosequencing and short-chain fatty acid (SCFA) analysis using GC-FID.ResultsSelective culture analysis showed no significant changes in cultured lactobacilli or bifidobacteria between the CE or DE and the cellulose-negative control at any time point measured (0, 5, 10, 24, 36, 48 h). Following metagenomic analysis, the CE and DE significantly altered the relative abundance of several families including Lachnospiraceae and genera including Streptococcus, Ruminococcus and Parabacteroides of human fecal bacterial populations in comparison to cellulose after 24 h. The concentrations of acetic acid, propionic acid, butyric acid and total SCFA were significantly higher for both the CE and DE compared to cellulose after 10, 24, 36 and 48 h fermentation (p < 0.05). Furthermore, the acetate:propionate ratio was significantly reduced (p < 0.05) for both CD and DE following 24, 36 and 48 h fermentation.ConclusionThe microbiota-associated metabolic and compositional changes noted provide initial indication of putative beneficial health benefits of L. digitata in vitro; however, research is needed to clarify if L. digitata-derived fiber can favorably alter the gut microbiota and confer health benefits in vivo.
Highlights
Macroalgae as a food resource remains a substantial component of the human diet with over 2 million kg of edible seaweed harvested globally every year [1]
The Bacteroidetes species have considerable metabolic plasticity owing to an extensive array of Carbohydrate-Active Enzymes (CAZymes) including seaweed-glycan-degrading enzymes [31, 57], which allow them to catabolize the wide range of polysaccharides present in the human diet
The simulated digestion used in the current study provided indications that digestion-resistant polysaccharides present within the Crude extract (CE) and depolymerized CE extract (DE) extract had the potential to be extensively fermented by the human microbiota, which corroborates previous studies which have demonstrated that isolated laminarin, fucoidan and alginate are resistant to simulated gastrointestinal digestion [45]
Summary
Macroalgae as a food resource remains a substantial component of the human diet with over 2 million kg of edible seaweed harvested globally every year [1]. Each fiber source will exert different effects on the microbiota as the fermentation properties of non-digestible polysaccharides are strongly influenced by the monomer composition, type of bond, and degree of polymerization (DP) [9, 17]. Brown seaweeds are known to be a rich source of fiber with the presence of several non-digestible polysaccharides including laminarin, fucoidan and alginate These individual polysaccharides have previously been shown to favorably alter the gut microbiota composition and activity albeit the effect of the collective brown seaweed fiber component on the microbiota remains to be determined. Methods This study investigated the effect of a crude polysaccharide-rich extract obtained from Laminaria digitata (CE) and a depolymerized CE extract (DE) on the gut microbiota composition and metabolism using an in vitro fecal batch culture model though metagenomic compositional analysis using 16S rRNA FLX amplicon pyrosequencing and short-chain fatty acid (SCFA) analysis using GC-FID. Conclusion The microbiota-associated metabolic and compositional changes noted provide initial indication of putative beneficial health benefits of L. digitata in vitro; research is needed to clarify if L. digitata-derived fiber can favorably alter the gut microbiota and confer health benefits in vivo
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