Antioxidant activity of brown alga Saccharina bongardiana from Kamchatka (Pacific coast of Russia). A methodological approach

The present study aims to investigate the levels of polyphenols and antioxidant activity in one of the most important commercial species of seaweeds in Kamchatka, an edible brown seaweed Saccharina bongardiana. Six extracts of S. bongardiana, acetone, methanol, ethanol, and the respective 70 % aqueous solutions, were assessed for total phenol content in order to determine the most efficient extracting solvent. The total phenol content was measured by the Folin-Ciocalteu method and expressed as phloroglucinol equivalents (PGE). The antioxidant tests used were 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay, linoleic acid-beta carotene oxidation inhibiting assay, and Fe2+ ion chelating method. Higher phenolic contents were obtained using aqueous organic solvents, as compared to the respective absolute solvents; 70 % acetone was found to be the most efficient solvent (1.039 mg PGE 100 mg(-1) dry algal powder). High significant correlations were noted between total phenol content and the tested antioxidant activities; so the aqueous organic extracts exhibited the highest antioxidant activities versus DPPH radicals (EC50 values of 0.6-1.1 mg dry weight (DW) mL(-1)), linoleic acid-beta carotene oxidation (74-78 % at 0.8 mg DW mL(-1)), as well as ferrous ions (EC50 values of 5.0-7.9 mg DW mL(-1)). Some methodological recommendations regarding the assays used and the expression of results are proposed.