title: A sulfated galactan with antioxidant capacity from the green variant of tetrasporic Gigartina skottsbergii (Gigartinales, Rhodophyta).
abstract: 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. (1)H and (13)C 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.
authors.affiliation: Departamento de Ciencias del Ambiente, Facultad de Química y Biología, Universidad de Santiago de Chile, Av. B. O'Higgins 3363, Santiago, Chile.
authors.forename: Tamara
authors.initials: T
authors.lastname: Barahona
authors.forename: María V
authors.initials: MV
authors.lastname: Encinas
authors.forename: Andrés
authors.initials: A
authors.lastname: Mansilla
authors.forename: Betty
authors.initials: B
authors.lastname: Matsuhiro
authors.forename: Elisa A
authors.initials: EA
authors.lastname: Zúñiga
mesh_terms: D000975:Antioxidants / Q000737:chemistry* / Q000302:isolation & purification / Q000494:pharmacology*; D052160:Benzothiazoles; D004579:Electron Transport; D005685:Galactans / Q000737:chemistry* / Q000302:isolation & purification / Q000494:pharmacology*; D017665:Hydroxyl Radical / Q000737:chemistry; D000461:Rhodophyta / Q000737:chemistry*; D013431:Sulfates / Q000737:chemistry*; D013451:Sulfonic Acids / Q000737:chemistry; D013844:Thiazoles / Q000737:chemistry
chemical_list: D000975:Antioxidants; D052160:Benzothiazoles; D005685:Galactans; D013431:Sulfates; D013451:Sulfonic Acids; D013844:Thiazoles; C002502:2,2'-azino-di-(3-ethylbenzothiazoline)-6-sulfonic acid; D017665:Hydroxyl Radical