Intra-thallus phlorotannin content and antioxidant activity in Phaeophyceae of temperate waters

This study focuses on the intra-thallus variation in phlorotannin content and antioxidant activity in temperate brown seaweeds. Two species of Fucales ( Ascophyllum nodosum and Sargassum muticum ) and two species of Laminariales ( Laminaria digitata and L. hyperborea ) were collected from the shoreline of Brittany (France). Both Fucales contained high phenolic levels along their thallus (ca. 5% DW in A. nodosum and 6% DW in S. muticum ). No significant differences were found between vegetative and reproductive parts of A. nodosum . In contrast, intra-thallus and inter-specific variations were observed in phenolic contents of the two species of Laminariales studied. In L. digitata , phenolic content was about 0.2% DW, with a maximum in the holdfast, whereas in L. hyperborea , it averaged about 2.6% DW, with the highest value measured in the basal part of the old blade. In both species, phlorotannin contents were lower in the meristematic region. Intra-thallus variations of the antioxidant activity measured by the DPPH (2,2-diphenyl-1-picrylhydrazyl) method were also detected. Antioxidant activity was correlated to the phenol contents of the different parts of thalli in three species. In L. digitata , no activity was found because of low phenol levels. The observed variations in both the antioxidant activity and the phenol content could result from qualitative features of the phenolic pool.