Antioxidant properties of supercritical extracts of brown algae

   Macroalgae is a unique feedstock capable of producing significant biomass in a fairly short time and synthesizing various chemical compounds, including specific biologically active substances that exhibit different biological activity. The study of antioxidant, antibacterial, antiviral, anti-inflammatory, and other properties of the biologically active substances of brown algae constitutes a relevant problem.   The present study aims to evaluate the antioxidant properties of supercritical extracts of the brown algae Saccharina japonica and Ascophyllum nodosum.   The content of carotenoids, phenolic compounds, and mannitol was determined using a spectrophotometric method. The metal content was analyzed using atomic absorption spectrometry. The antioxidant activity was evaluated according to antiradical activity using a 2,2-diphenyl-1-picrylhydrazyl radical, hydroxyl ion binding activity, and Fe+2 chelating activity, as well as the superoxide radical scavenging activity. The studies on the supercritical extracts of brown algae revealed a rather high content of fatty acids and phenolic compounds, with fatty acids most abundantly present in the supercritical extract of Ascophyllum nodosum; phenols, mannitol, and pigments, in the extract of Saccharina japonica. The predominant macroelement in the supercritical extracts of brown algae is potassium, with the maximum content found in the extract of Saccharina japonica. The supercritical extracts of brown algae are safe in terms of the contents of nitrosamines, polychlorinated biphenyls, toxic elements, and radionuclides. The most pronounced antiradical properties were shown by the supercritical extract of Saccharina japonica. The highest hydroxyl ion binding activity was noted in the supercritical extract of Saccharina japonica. In terms of superoxide radical scavenging activity, the maximum activity was exhibited by the extract of Ascophyllum nodosum. The Fe+2 chelating activity was about the same for the supercritical extracts of brown algae, with the maximum activity (38.7 %) observed for the extract of Ascophyllum nodosum.