Abstract
Phenolic components from the edible brown seaweed, Ascophyllum nodosum, have been associated with considerable antioxidant activity but also bioactivities related to human health. This study aims to select and identify the main phlorotannin components from this seaweed which have been previously associated with potential health benefits. Methods to enrich phenolic components then further select phlorotannin components from ethanolic extracts of Ascophyllum nodosum were applied. The composition and phenolic diversity of these extracts were defined using data dependent liquid chromatography mass spectroscopic (LC-MSn) techniques. A series of phlorotannin oligomers with apparent degree of polymerization (DP) from 10 to 31 were enriched by solid phase extraction and could be selected by fractionation on Sephadex LH-20. Evidence was also obtained for the presence of dibenzodioxin linked phlorotannins as well as sulphated phlorotannins and phenolic acids. As well as diversity in molecular size, there was evidence for potential isomers at each DP. MS2 fragmentation analyses strongly suggested that the phlorotannins contained ether linked phloroglucinol units and were most likely fucophlorethols and MS3 data suggested that the isomers may result from branching within the chain. Therefore, application of these LC-MSn techniques provided further information on the structural diversity of the phlorotannins from Ascophyllum, which could be correlated against their reported bioactivities and could be further applied to phlorotannins from different seaweed species.
Highlights
Phlorotannins are dehydro-polymers of phloroglucinol units associated with brown seaweeds (Phaeophyceae) [1,2,3]
We report on the enrichment and fractionation of phlorotannins and related phenolics from Ascophyllum nodosum and apply a series of liquid chromatography mass spectrometric (LC-MSn ) methods to define their structural diversity
The reasonably high Total phenol content (TPC) in the unbound material may be due to non-phenolic material that cross-reacts with the non-specific Folin reagent [26]
Summary
Phlorotannins are dehydro-polymers of phloroglucinol units associated with brown seaweeds (Phaeophyceae) [1,2,3] They appear to play a defensive role in the seaweeds, protecting against herbivory [4,5,6] and UV-B radiation e.g., [7]. Their levels vary with season, developmental stages and abiotic stresses [8,9,10,11] and it has been suggested that there is balance between a structural role in the algal cell wall and these protective roles [12]. If the phloroglucinol units are only linked by phenyl -C-C bonds, they are termed fucols; if they are only linked by -C-O-C- aryl ether bonds, they are termed phlorethols and if both linkages are present they are termed fucaphlorethols.
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