Profiling phlorotannins from Fucus spp. of the Northern Portuguese coastline: Chemical approach by HPLC-DAD-ESI/MSn and UPLC-ESI-QTOF/MS

Several attempts have been made in recent years to fully characterize phlorotannin-rich extracts. Nevertheless, this remains a challenging quest, not only because of seaweed complex chemical composition, but also due to the diverse structural assemblage within phlorotannin molecules (i.e., type of linkage, modification site, and number of additional hydroxyl groups). In this work, 22 phlorotannins were tentatively identified and their presence confirmed, in purified extracts obtained from four Fucus species, by HPLC-DAD-ESI/MSn and UPLC-ESI-QTOF/MS analyses. The characterized phlorotannins exhibited molecular weights ranging from 370 to 746 Da and relatively low degree of polymerization (3-6 phloroglucinol units). Isomers of fucophlorethol, dioxinodehy-droeckol, difucophlorethol, fucodiphlorethol, bisfucophlorethol, fucofuroeckol, trifucophlorethol, fucotriphlorethol, tetrafucophlorethol, and of fucotetraphlorethol were identified. Among the analysed phlorotannin purified extracts, only the ones wild-sourced and from aquaculture-grown Fucus vesiculosus exhibited five and six-ringed phloroglucinol oligomers in their composition. The remaining extracts from Fucus guiryi, Fucus serratus and Fucus spiralis were richer in both trimers and tetramers. The variability observed for the overall phlorotannin composition points to the influence of species-specific and/or external factors. As far as we know, mass spectra confirming the presence and degree of polymerization of phlorotannins in Portuguese-sourced brown macroalgae, specifically F. guiryi and F. serratus, as well as of aquaculture-grown F. vesiculosus, are not found in literature. The information gained in this work ascertains the role of advanced analytical tools in facilitating the use of this valuable natural resource for the development of macroalgal-based products, opening doors for future application of phlorotannin-rich extracts in the commercial areas related to nutraceuticals, pharmaceuticals, and cosmetics.