Plants arabinogalactans: From structures to physico-chemical and biological properties.

Arabinogalactans (AGs) are plant heteropolysaccharides with complex structures occasionally attached to proteins (AGPs). AGs in cell matrix of different parts of plant are freely available or chemically bound to pectin rhamnogalactan. Type I with predominantly ß-d-(1 â†’ 4)-galactan and type II with ß-d-(1 â†’ 3) and/or (1 â†’ 6)-galactan structural backbones construct the two main groups of AGs. In the current review, the chemical structure of AGs is firstly discussed focusing on non-traditional plant sources and not including well known industrial gums. After that, processes for their extraction and purification are considered and finally their techno-functional and biological properties are highlighted. The role of AG structure and function on health advantages such as anti-tumor, antioxidant, anti-ulcer- anti-diabetic and other activites and also the immunomodulatory effects on in-vivo model systems are overviewed.

Characterization of arabinogalactan-rich mucilage from Cereus triangularis cladodes.

Cereus triangularis (Cactaceae) is a cactus used in food decoction as a traditional medicine in the North region of Madagascar to reduce stomach ache and intestinal diseases. Hydrocolloids were sequentially extracted from its cladodes with a yield of 24% (240 mg/g based on dried cladodes powder). Structural analyses has revealed that this polysaccharide with a molecular mass of 8430,000g/mol was mainly composed of a galactan backbone of a (1 → 4) linked ß-d-Galp residues probably substituted at position 3 by L-arabinofuranosyl residues. In vitro antioxidant activity of this arabinogalactan-rich fraction was detected and quantified by radical DPPH scavenging, hydroxyl radical scavenging, radical anion superoxide scavenging and reducing power method.

Highly sulphated galactan from Halymenia durvillei (Halymeniales, Rhodophyta), a red seaweed of Madagascar marine coasts.

Halymenia durvillei is a red seaweed with a great potential as sulphated galactan producer collected in the coastal waters of small island of Madagascar (Nosy-be in Indian Ocean). To elucidate the structure of its polysaccharide, NMR (1H and 13C), FTIR, HPAEC and different colorimetric methods were carried out. It has been shown that this polysaccharide, consisted mainly of galactose, was branched by xylose and galactose in minor amounts. Arabinose and fucose were also detected. This galactan was found highly sulphated (42%, w/w) and pyruvylated (1.8%, w/w). Analysis of glycosidic linkages by CPG-MS and 13C NMR indicated that the polysaccharide has the defining linear backbone of alternating 3-beta-D-galactopyranosyl units and 4-linked alpha-L/D-galactopyranosyl residues. 3,6-Anhydrogalactose units have been also detected in minor quantity. This lambda-carrageenan like polysaccharide has shown original sulphatation patterns with 2-O (26%) or 2/6-O (58%) sulphated 3-linked beta-D-galactopyranosyl units and 6-O (19%) or 2/6-O (47%) 4-linked alpha-L/D-galactopyranosyl residues.