Seaweed represents a sustainable and underexplored source of bioactive compounds with potential applications in health, functional food and well-being. This study presents the characterization of extracts from the macroalgae, Gracilaria sp. (red), Ulva sp. (green) and Fucus vesiculosus (brown), cultivated in ALGAplus company (Portugal). The aim was to identify promising bioactive compounds for the future development of high-value products for potential health and well-being applications.

The obtained aqueous extracts were purified by precipitation with ethanol, resulting for each seaweed in a polysaccharide-free extract and a polysaccharide fraction. All the extracts and fractions were analysed for total phenolic content (TPC), antioxidant activity by DPPH method and bioactive compound profile by high-performance liquid chromatography with diode array detection (HPLC-DAD).

The polysaccharide-free extract from the red seaweed showed the highest total phenolic content (0.76 mg/mg) and antioxidant activity (27.4% for 0.5 mg/mL). An enrichment of compounds was also observed in the obtained purified extract’s HPLC-DAD chromatographic profile compared to the initial extract. Therefore, the identification of the compounds present in this purified extract by high-resolution mass spectrometry will be presented. Safety assessments of the purified extract included in vivo tests using Artemia salina and in vitro MTT assays on HaCaT keratinocytes. No toxicity was observed, and 96% cell viability was obtained, respectively.

The obtained results reinforce the potential of Gracilaria sp. as a promising marine biotechnological resource of non-toxic, bioactive and antioxidant compounds with application in dermatological formulations, food supplements and other innovative solutions in the areas of health and well-being.