Chemical structures of phlorotannins from abundant brown seaweeds along tropical and temperate Atlantic coasts and their associated activities

Abstract

Abstract Phlorotannins are highly hydroxylated polymeric metabolites produced by brown seaweeds, and known for their wide range of bioactivities, which makes them promising for various fields of applications. It is strongly suspected that the potential of their bioactivities is directly related to their chemical structure. The present study aims to characterize the phlorotannin chemical structure of abundant brown macroalgae: two species were collected in the tropical Atlantic Ocean (Sargassum natans I, S. natans VIII and S. fluitans III), while the others (Sargassum muticum, Ascophyllum nodosum, Laminaria digitata and L. hyperborea) were sampled either on the coasts of Brittany or Normandy (France) and are already valorised by French companies. Phlorotannins were extracted and purified to obtain phlorotannin-rich fractions. These fractions were tested for their radical scavenging activity as well as their antibacterial activity against two bacterial strains of interest for human health and cosmetics. In parallel, the chemical structure of phlorotannins was elucidated through 2-Dimensions Nuclear Magnetic Resonance spectroscopy (2D-NMR). A. nodosum phlorotannin-purified fraction exhibited the highest phenolic content, the highest radical scavenging activity and the highest antibacterial activity against bacterial strains. Phlorethol-type phlorotannins were identified in S. natans I and S. muticum, while fucophlorethol-type phlorotannins were identified in S. natans VIII, L. hyperborea and A. nodosum. The levels of activities seem to be linked with the structure and the quantity of phlorotannins which emphasize the need for further investigations in order to sustain the use of algal phlorotannins as bioactive metabolites for the human well-being sector.