Arabinogalactans larch

The water-extractable arabinogalactans are most abundant in the larches (Larix spp.). The most extensively studied has been that of the heartwood of the western larch Larix occidentalis). The source, production, properties, and potential uses of this polysaccharide are reviewed in Chap. 10.2.2. 

The structural information on larchwood arabinogalactan has been reviewed (162). Its main structural features are represented by the structure in Fig. 4.1. 

Units such as these (MW-2200 daltons) are joined by sugar units vulnerable to periodate oxidation to give polymers with a wide range of molecular weights of from 16-18000 to 100000 (49, 60). 

It has been reported that the ratio of galatose to arabinose in the arabinogalactan of Larix occidentalis increases and that the number-average molecular weight of the polymer decreases with increasing age of the wood (67, 154). 

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Larch Gum. Larch gum [37320-79-9] (larch arabinogalactan) is obtained by water extraction of the western larch tree, iLarix occidentalism the heartwood of which contains 5—35% on a dry wood basis. In the early 1960s, a countercurrent hot water extraction system was developed, and the gum was produced commercially by the St. Regis Paper Co. under the trade name Stractan. The potential production capacity of this gum is 10,000 t/yr based on the wood residues from the lumber industry. However, the product could not compete with gum arabic, and commercial production is now limited to small batches for a specific medical appHcation. 

Larch arabinogalactan is approved in 21 CFR 172.610 as a food additive for use as an emulsifier, stabilizer, binder or bodying agent for essential oils and noimutritive sweeteners, flavor bases, nonstandardized dressings, and pudding mixes. It has also been used in the preparation of cosmetic and pharmaceutical dispersions and as an emulsifier in oil—water emulsions (69). Industrially, the main use has been in Hthography as a gum arabic substitute. 

Within the scope of this review, the contributions of the last decade concerning cell-wall polysaccharides isolated from woody and other plant tissues will be reviewed according to the above-proposed classification of hemicelluloses including larch arabinogalactans. The present review article updates and extends previous reviews [3-5] and will focus in particular on new investigated plant sources, isolation methods, structural features, physicochemical and various functional properties of hemicelluloses. Attention will also be paid to the modification of isolated hemicelluloses or hemicellulosic materials and the appHcation possibiUties of hemicelluloses and their derivatives, including their use for the production of composite materials and other biomaterials. 

A monograph on the larch arabinogalactan has been published, containing pharmacokinetics, clinical indications, the lack of side-effects and dosage [60]. In a report from 2003, the effect over time of in-vivo administration of the larch arabinogalactan on the immune and hemopoietic cell... 

KELLY G s (1999) Larch arabinogalactan Clinical relevance of a novel immune-enhancing polysaccharide. Med Rev, 4(2) 96-103. 

Larch arabinogalactans, 4 718 LaRC-TOR series polyimides, 20 282 Lard, in soap making, 22 735 Large block carbons, 12 764 Large bulk superconductors, 23 869... 

Recent investigations by Bouveng and Lindberg124 have shown that Western-larch arabinogalactan is more complex than previously supposed. 

Mild, acid hydrolysis of European-larch arabinogalactan results in the formation of 3-0-/3-L-arabinopyranosyl-L-arabinose (XXXIX). 26 Although this disaccharide has been isolated as an acid-reversion product from L-arab-inose,131 it is accompanied under these conditions by two other arabinose-containing disaccharides, neither of which was detected in the larch polysaccharide hydrolyzate. Since hydrolysis of methylated -galactan gave approximately equimolar proportions of 2,3,4-tri-O-methyl-L-arabinose and 2,5-di-O-methyl-n-arabinose, traces of 2,3,5-tri-O-methyl-L-arabinose, and no mono-O-methyl-L-arabinose, it is clear that the L-arabinose units must arise from an arabinogalactan rather than from an arabinan, and that the majority of these must be present in 3-0-/3-L-arabinopyranosyl-L-arabino-furanose side-chains (XLV) linked, in some way as yet unknown, to the framework of D-galactose units (XLI). 

Agars, alginates, carrageenans, furcellaran Extracts Larch arabinogalactan, pectins... 

Some hemicelluloses have practical applications such as larch arabinogalactan, which is a water-soluble gum found in the heartwood of trees from Larix genus, and which is used in processed food as an emulsifier, or in pudding mixes, etc. A Py-GC/MS study of arabinogalactan from larch wood indicated the presence of the galactose unit and of arabinose unit in the ratio 6 1, as it is known in this material. The arabinose units were identified mainly by the formation of 1,4-anhydro-L-arabinopyranose, which elutes faster than the corresponding hexoses. The structure shown below was therefore confirmed by Py-GC/MS [64]. 

Like most wood polysaccharides, the larch arabinogalactans probably differ only in minor structural details from one species to another, the general pattern remaining the same for the entire genus. 

Larch arabinogalactan has a backbone of (l-3)-linked (3-D-galactopyranosyl units each of which contains a side chain at position C-6. Most of these side chains are galactohiosyl units containing a (l-6)-p-D-linkage. Another side chain type that occurs is a single L-arabinofuranose unit or 3-0-(3-L-arabinopyranosyl)-a-L-arabinofuranosyl units. The preliminary X-ray fibre diffraction data [16] proved that western larch arabinogalactan can adopt a triple helix conformation. 

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