Reference Number: 465
Brown seaweeds such as Ascophyllum nodosum are a rich source of phlorotannins (oligomers and polymers of phloroglucinol units), a class of polyphenols that are unique to Phaeophyceae. At present, there is no information on the bioavailability of seaweed polyphenols and limited evidence on their bioactivity in vivo. Consequently, we investigated the gastrointestinal modifications in vitro of seaweed phlorotannins from A. nodosum and their bioavailability and effect on inflammatory markers in healthy participants. In vitro, some phlorotannin oligomers were identified after digestion and colonic fermentation. In addition, seven metabolites corresponding to in vitro-absorbed metabolites were identified. Urine and plasma samples contained a variety of metabolites attributed to both unconjugated and conjugated metabolites (glucuronides and/or sulphates). In both urine and plasma, the majority of the metabolites were found in samples collected at late time points (6-24 h), suggesting colonic metabolism of high-molecular-weight phlorotannins, with three phlorotannin oligomers (hydroxytrifuhalol A, 7-hydroxyeckol, C-O-C dimer of phloroglucinol) identified in urine samples. A significant increase of the cytokine IL-8 was also observed. Our study shows for the first time that seaweed phlorotannins are metabolised and absorbed, predominantly in the large intestine, and there is a large inter-individual variation in their metabolic profile. Three phlorotannin oligomers present in the capsule are excreted in urine. Our study is the first investigation of the metabolism and bioavailability of seaweed phlorotannins and the role of colonic biotransformation. In addition, IL-8 is a possible target for phlorotannin bioactivity.
Significance of this study to the baker:
Here at the Sourdough School we not only incorporate seaweed into our botanical blends, but also our sourdough bread.
The darker seaweed algae such as the brown seaweed mentioned in this study are not only rich in minerals and polysaccharides but also contain more bioactive properties such as polyphenols. These polyphenols are found to be high in antioxidants, and display anti-inflammatory and antimicrobial properties. This laboratory based study shows that the seaweed phlorotannins (polyphenol) are metabolised and absorbed predominantly in the large intestine suggesting a role in gastrointestinal health. These polyphenols from the seaweed, like other polyphenols, behave like a prebiotic. They are fed on by our beneficial gut microbes, providing the greater health benefits associated with building a healthy gut microbiome.