Antioxidants from Australian fucoid seaweeds: Comparisons with well-characterised North Atlantic species

Oxidative stress is implicated in the development of numerous chronic diseases, increasing interest in natural sources of antioxidant compounds. Fucoid brown seaweeds are rich in bioactive metabolites, including phenolic compounds, polysaccharides and pigments, with reported antioxidant activities and promising applications across health-related industries. However, Australian fucoids remain largely underexplored compared with commercially harvested Northern Hemisphere species, and their biochemical diversity and antioxidant potential require further characterisation. High endemism and exposure to intense environmental pressures, including high UV radiation and ocean warming, could favour the production of unique defence molecules in Australian fucoids. This study evaluated the composition and antioxidant potential of four ecologically dominant Australian fucoids ( Hormosira banksii , Durvillaea potatorum , Cystophora torulosa and Phyllospora comosa ) compared with five well-characterised North Atlantic species ( Fucus spiralis , Ascophyllum nodosum , Fucus serratus , Himanthalia elongata and Sargassum muticum ). 1 H HR-MAS NMR spectroscopy was used to fingerprint global molecular composition, whilst targeted extractions were performed to quantify major bioactive compounds (phlorotannins, fucoxanthin, alginates and fucoidans) and evaluate their antioxidant activities using DPPH and FRAP assays. Amongst the compounds investigated, phlorotannins were identified as the strongest contributors to antioxidant potential, combining high concentrations with strong radical scavenging and reducing activities. Although Australian fucoid extracts did not exhibit higher antioxidant potential than their North Atlantic counterparts overall, with A. nodosum displaying the highest phlorotannin concentrations, they remained comparable to the other well-characterised species whilst exhibiting distinct species-specific molecular profiles. These findings highlight the antioxidant potential of Australian fucoids and support further characterisation of their phlorotannins towards sustainable seaweed-based applications.