Arabinans

The pentosan polysaccharides, xylan and arabinan, commonly known as hemiceUulose, are the principal precursors of furfural and are always found together with lignin and cellulose in plant materials. 

Arabinan. This highly soluble polymer is found in the extracts of many fmits and seeds, in the boiling water extracts of pine wood (127), in the extracts of marshmallow roots (A/t/jaea officina/is) (128), and aspen (63) and willow (Sa/ix a/ba F) (129) bark. Because arabinan can be isolated from mildly degraded pectin fractions, it is often difficult to determine whether it is a hemiceUulose or a labile fragment of a larger polysaccharide and/or lignin complex. Arabinans have a complex stmcture composed almost entirely of 5-linked a-L-arabinofuranosyl units with similar residues linked to them at C-2 and/or C-3 and is soluble in 70% aqueous methanol solution. 

Scientific name/Common name Glucan Xylan Galactan Arabinan Man nan Uronic anhydride Acetyl Lignin Ash... 

A few examples of pure arabinans with effect in the complement system have been isolated from, for example, the fruits of Ziziphus jujuba (a-2,5-arabinofuranan) and from the roots of Bupleurum falcatum (Q -3,5-arabino-furanan-Q -l,4-glucan complex) [12,13]. 

Fig. 2 Average structure of the hairy or ramified region of an apectic substance, with a rhamnogalacturonan I backbone substituted at position 4 of the rhamnose units with arabinan and arabinogalactan type II side chains...

Isolation from sugar beet cell walls of arabinan oligosaccharides esterified by two ferulic acid monomers / / Plant Physiology. V. 134. P. 1173-1180. 

The length of the arabinan side chains present in subunit II may vary between 30 and 50 arabinose residues and several of these chains might be connected to the rhamnogalacturonan backbone which consists of only 8-10 sugar residues (ratio of rhamnose to galacturonic acid is 0.2 to 0.4). The arabinans might be connected directly to a rhamnose residue in the backbone or via one or more galactose residues [41]. 

The low amounts in 3- and 3,6-linked galactosyl, in 3- and 5-linked arabinosyl residues may be due to the presence of contaminating arabinogalactans and arabinans in apple and tomato juice RG-II preparations. 

Echinacea-polysaccharide II consists of arabino-3,6-P-galactan part, rhamnogalacturonan part and arabinan part [5], therefore it is suggested that the polysaccharide may be certain ramified region of pectic polysaccharide. 

Analysis of the products which become water-soluble after extrusioncooking showed that feroylated heteroxylans and glucans were solubilised from wheat bran (10), arabinans, heteroxyalans and pectins from pea hulls (11,12), and pectins from the other sources (13,14). 

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