In vitro antioxidant properties of red algal polysaccharides

The present study was devoted to in vitro antioxidant properties of lambda-, iks-, kappa-, kappa/beta- and kappa/iota-carrageenans from red algae of Gigartinaceae and Tichocarpaceae families collected from the Russian Pacific Coast. In vitro antioxidant capacity of carrageenans with different structural types was assessed by measuring their ferric-reducing antioxidant capacity, relative antioxidant capacity (phosphomolybdenum assay), and their scavenging effect on hydroxyl radicals, superoxide anion, nitric oxide and hydrogen peroxide. Influence of pH value on potential antioxidant capacity was also been investigated by means of linoleic model system. The reducing capacity of the investigated carrageenans was not much expressed, and capacity of the commercial polysaccharide samples was negligible. Iks-carrageenan containing three sulphate groups per disaccharide unit and a 3,6-anhydrogalactose unit was among the most effective superoxide anion (54.83% at the concentration of 1 mg/mL) and nitric oxide scavengers (37.26% at the concentration of 0.25 mg/mL) and the only polysaccharide possessing iron ion chelating capacity. Antioxidant actions of lambda-, iks-, kappa-, kappa/beta- and kappa/iota-carrageenans against reactive oxygen/nitrogen species depend on polysaccharide concentration and such fine structural characteristics as presence of hydrophobic 3,6-anhydrogalactose unit, amount and position of sulphate groups, and an oxidant agent, on which sample antioxidant action is directed. The results indicated that carrageenans possess antioxidant capacity in vitro, and this action notably depends on the structure of the polysaccharide itself than the reducing capacity of the polysaccharides.