Polysaccharides bark

The common hemiceUulose components of arborescent plants are listed in Table 3. Xylans, arabinogalactans, and pectic substances are common to all while only traces (if at all) of glucomaimans are found in the cell walls of bamboo. Other polysaccharides are found in trace amounts in wood as well as in bark, growing tissues, and other specialized parts of trees. 

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. 

A. Deters, A. Dauer, E. Schnetz, M. Fartasshc and A. Hensel, High molecular compounds (polysaccharides and proanthocyanidins) from Hamamelis virginiana bark influence on human skin keratinocyte proliferation and differentiation and influence on irritated skin. Phytochemistry 58 (2001) 949-958. 

Lycium chinense Miller Di Gu Pi (Matrimony vine) (root bark) Cinnamic acid, betaine, peptides, acyclic diterpene glycosides, polysaccharide, kukoamines.33 Lower blood sugar and blood pressure, antipyretic, stimulate uterine contraction, antibacterial. 

In addition to the previously described polysaccharides, which are classified on a structural basis as glycans of various types (for example, D-glucans, D-mannans, and D-xylans), a wide variety of complex structures is present in plants. These are difficult to classify on a structural basis they are commonly known as plant gums, and seed and bark mucilages. 

We started a series of experiments to dissolve celluloses, pulps, and samples of wood or bark in acetylating media containing dimethyl-formamide, followed by hydrolysis to achieve rapid and complete formation of monomeric sugars. The main purpose was to develop a rapid and reproducible method for the determination of the sugar units present in polysaccharides, particularly those resistant to milder treatment. 

Fang, P., McGinnis, G. D., and Wilson, W. W. (1981). Thermal fragmentation for the identification of pyrolytic products from bark polysaccharides. Anal. Chem. 53 2172-2174. 

Plant gums, which occur as exudates on the bark or leaves of trees, are salts of polyuronic acids and are usually freely soluble in water. It is often difficult to decide whether such polysaccharides are homogeneous, but a beginning has now been made in the determination of their structures. Weak linkages have been shown to be present, and it is possible to remove portions of the molecules that are readily hydrolyzable by mild acid, leaving a more stable acidic residue. The structure of the gums appears to depend upon the source, and some studies are complicated by the fact that the botanical origin of the gum was not known with certainty. 

Nephritis is an autoimmune disease caused by activation of the complement system. Cinnamon cortex and cinnamon oil inhibited complement formation in vitro. Cinncassiol C, and its glucoside, the cinncassiols C2 and C3 and cinncassiol D, and its glucoside were reported to possess anticomplementary activity. A water-soluble polysaccharide isolated from the cinnamon extract showed complement system activity (Tang and Eisenbrand, 1992). 2-Hydroxycinnamaldehyde and 2-benzyloxy cinnamaldehyde isolated from the stem bark of cinnamon possessed immunomodulatory effects (Koh et al., 1999). 

A number of plants and some trees contain a white, milky liquid that is released when the stem or bark is cut. The liquid is called a latex from the Latin meaning liquid. Common sources include dandelions, milkweed, goldenrod, and potted rubber plants. Rubber trees, from which substantial quantities of latex can be harvested, grow in some tropical areas of the world. A major constituent of this latex is a homopolymer of isoprene (2-methyl-1,3-butadiene), called polyisoprene. Polyisoprene, as well as a number of other elastomers, has a carbon-carbon double bond in every repeat unit. The properties of polyisoprene are the result of the presence of these double bonds. Just as stereochemistry plays a critical role in both proteins and polysaccharides, we will see its importance here. 

Timell, T. E. (1965). Wood and bark polysaccharides. In "Cellular Ultrastructure of Woody Plants" (W. A. C6te, Jr., ed.), pp. 127-156. Syracuse Univ. Press, Syracuse, New York. Timell, T. E. (1967). Recent progress in the chemistry of wood hemicelluloses. Wood Sci. Technol. 1,45-70. 

Polysaccharides, lignin, and suberins are the principal cell wall constituents of bark. 

Polysaccharides. The bast fibers are essentially built up by polysaccharides. Cellulose dominates (roughly 30% of the dry bark weight) in addition to the hemicelluloses, which are of the same type as in wood (see Section 3.3). 

In addition, a highly branched arabinan probably occurs in many barks, and especially pines. The connecting strands of the sieve elements are surrounded by a polysaccharide called callose, which is a (1 —> 3)-/3-D-glucan. 

These results may be compared with viscosities obtained in a similar way from conifer bark extracts which, while heterogeneous, contain polymeric pro-cyanidins or mixed polymeric procyanidins and prodelphinidins as their predominant components (2). For example, Weissman (25) reported a viscosity of 65 mPa-s for a 30% solution of the water extract from Pinus oocarpa bark, and Dix and Marutsky (26) obtained a value of 31 mPa-s for a similar solution from Picea abies bark. These viscosities are similar to those observed for the 30% procyanidin polymer solutions. They indicate that the viscosities of these bark extract solutions are dominated by the proanthocyanidins and that there is little influence from any accompanying polysaccharides-as already suggested by Weissmann (25)-in contrast to wattle extracts where gums play an important role in determining solution viscosities (7). 

When P. radiata bark is extracted by sulfite-carbonate, the solution viscosities are much lower. For example, Woo (30) reported a viscosity of 1,600 mPa-s for a 45% solution of Tannaphen, a commercial tannin extract from P. radiata bark that contains approximately 70% proanthocyanidins. When extracted with sulfite-carbonate, the proanthocyanidins will be partly depolymerized 31), which will cause a fall in viscosity. Whether the very high viscosities observed for aqueous extracts by Yazaki and Hillis 29) are due to the P, radiata proanthocyanidins being of much higher molecular weight than other conifer tannins or due to complexation of the proanthocyanidins with the polysaccharide fraction 32) remains to be shown. 

Another gum analyzed by Py-GC is the cherry gum, which can be isolated from exudation of the bark of the cherry tree. The gum is a complex polysaccharide with a variable proportion of the acid components and neutrai sugars [6a]. A model composition of this gum is the following ... 

Polysaccharides of the xyloglucan may be of relatively widespread occurrence, and examples have been reported from the bark of Engel-mann spruce (Picea engelmann), 5 red-spruce compression-wood,155 the seeds of white mustard (Brassica alba),156 and sycamore callus-cells.157 The mustard156 and sycamore157 polysaccharides are charac-... 

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