A sulfated galactan with antioxidant capacity from the green variant of tetrasporic Gigartina skottsbergii (Gigartinales, Rhodophyta)

• Published in: Carbohydrate research Vol. 347; no. 1; pp. 114 - 120
• Main Authors: Barahona, Tamara, Encinas, María V., Mansilla, Andrés, Matsuhiro, Betty, Zúñiga, Elisa A.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ltd 10.01.2012
• Subjects: antioxidant activity; Antioxidant capacity; Antioxidants - chemistry; Antioxidants - isolation & purification; Antioxidants - pharmacology; Benzothiazoles; carbon; carrageenans; Electron Transport; Galactans - chemistry; Galactans - isolation & purification; Galactans - pharmacology; galactose; Gigartina; Green variant red seaweed; Hydroxyl Radical - chemistry; hydroxyl radicals; lambda-carrageenan; nuclear magnetic resonance spectroscopy; polysaccharides; reaction kinetics; Rhodophyta - chemistry; stable isotopes; sulfates; Sulfates - chemistry; Sulfonic Acids - chemistry; Thiazoles - chemistry; λ Carrageenan; λ Carrageenan; Antioxidant capacity; Green variant red seaweed
• ISSN: 0008-6215; 1873-426X
• DOI: 10.1016/j.carres.2011.11.014

Proposed structure for the polysaccharide synthesized by the green variant of tetrasporic Gigartina skottsbergii. [Display omitted] ► The polysaccharide was composed of d-galactose and sulfate in a ratio of 1:0.65. ► The galactan presents similar structure to λ-carrageenan but with lower sulfation. ► Sulfate groups are located at position O-2 and O-6 of α- d-galactopyranosyl residue. ► The antioxidant capacity of the galactan was evaluated by different radicals. ► ORAC assay is an adequate method to measure the antioxidant capacity of D-galactan. The water soluble polysaccharide produced by the green variant of tetrasporic Gigartina skottsbergii was found to be composed of d-galactose and sulfate groups in a molar ratio of 1.0:0.65. 1H and 13C NMR spectroscopy studies of the desulfated polysaccharide showed a major backbone structure of alternating 3-linked β- d-galactopyranosyl and 4-linked α- d-galactopyranosyl units, and minor signals ascribed to 3- O-methyl-substitution on the latter unit. Ethylation analysis of the polysaccharide indicated that the sulfate groups are mainly located at position O-2 of 4-linked α- d-galactopyranosyl residue and partially located at positions O-6 of the same unit and at position O-2 of 3-linked β- d-galactopyranosyl residue, and confirmed the presence of 3- O-methyl-galactose in minor amounts (4.4%). The sulfated d-galactan presents a similar structure to λ carrageenan but with much lower sulfation at position O-6 of the α-residue and at position O-2 of β-residue. The antioxidant capacity of the sulfated d-galactan was evaluated by the peroxyl radicals (ORAC method), hydroxyl radicals, chelating activity, and ABTS + assays. Kinetic results obtained in these assays were compared with those obtained for the commercial λ carrageenan. The antioxidant activity toward peroxyl radicals was higher for commercial λ carrageenan, this agrees with its higher content of sulfate group. The kinetics of the reaction of both polysaccharides with hydroxyl and ABTS + radicals showed a complex mechanism, but the antioxidant activity was higher for the polysaccharide from the green variant of tetrasporic Gigartina skottsbergii.