Plants hemicelluloses

Endo-xylanases (1,4-p-D-xylan xylanohydrolase, EC 3.2.1.8), which hydrolyze mainly interior p-(l- 4)-D-xylosyl bonds in the plant hemicellulose xylan, have been isolated from many fungi and bacteria and occasionally from plants and invertebrates. Because xylan is one of the most common of all natural materials, and its removal or conversion is often desirable, the endo-xylanase family has high commercial as well as scientific interest. 

Antitumor Activity and Composition of Some Plant Hemicelluloses... 

Diequatorially linked polypyranose structures form fibres when the polysaccharides are undecorated - indeed, oligosaccharides beyond a degree of polymerisation of 6 become almost water insoluble. When, however, the backbone chain is substituted ( decorated ), as it is in the plant hemicelluloses, the decoration interferes with the parallel packing of the chains and much more soluble polymers result. 

Material Plant Hemicellulose Cellulose Crude Lignin Reference... 

Hemicellulose is a group of polysaccharides that can be found in the plant s cell wall that surrounds the cellulose, protein, lignin, and other materials that covalently bonded, hydrogen bonds, ionic bonds and interactions hydrophoby [35]. In plants, hemicellulose is a second polymer after cellulose that abundance in wood and cereals. It consists of approximately one-quarter to one-third of the plant material. This amount varies according to the type of plants, such as corn steins [28.0%], wheat straw [38.8%), rice straw [35.8%), and rye straw [36.9%). Hemicellulose serves as a supporter to cell wall and as an adhesive between single cells In plants [10]. 

Arabans high molecular mass, branched polysaccharides composed of t-arabinose linked 1,5 and 1,3 in furanose form (see carbohydrates). A. are found widely as components of plant hemicelluloses. 

C12H22O11 342.299 Structural unit in the glucomannans of plant hemicelluloses. Isol. from the partial acid hydrolysates of the glucomannans from Amorphophallus spp., white spruce (Pinus glauca), western hemlock (Tsuga heterophylla), red maple (Acer rubrum), eastern white pine (Pinus strobus), larch (Larix decidua), jack pine (Pinus bank-siana) and from Narcissus tazetta from hemicelluloses of lobolly pine (Pinus taeda) and in trace amounts from the acetolysates of the a-celluloses from white birch (Betula papyrifera) and slash pine... 

C12H22O11 342.299 Structural unit in the glucomannan of plant hemicelluloses. Isol. from partial acid hydrol. of Amorphophalus, spp., Picea glauca, Tsuga heterophylla, Acer rubrum and others. 

Perhaps in part due to the lack of commerical supply, hemicellulose has found relatively little industrial utility. The reported industrial applications for plant hemicellulose include their use as viscosity modifiers, gelling agents, tablet binders, or wet strength additives (/). Recently, there has been interest in the use... 

D-galactose, C HiiOe. Crystallizes in the pyranose form m.p. 1I8-120 C (monohydrate), 165-5" C (anhydrous). An isomer of glucose which is fairly widely distributed in plants. It is a constituent of raffinose and slachyose, of hemicelluloses, of pectin, of gums and mucilages, and of some glycosides. In animals it forms half the lactose molecule and is the sugar found in the brain. Chemically it is very similar to glucose. It has the structure... 

Hemicellulose [9034-32-6] is the least utilized component of the biomass triad comprising cellulose (qv), lignin (qv), and hemiceUulose. The term was origiaated by Schulze (1) and is used here to distinguish the nonceUulosic polysaccharides of plant cell walls from those that are not part of the wall stmcture. Confusion arises because other hemicellulose definitions based on solvent extraction are often used in the Hterature (2—4). The term polyose is used in Europe to describe these nonceUulosic polysaccharides from wood, whereas hemicellulose is used to describe the alkaline extracts from commercial pulps (4). The quantity of hemicellulose in different sources varies considerably as shown in Table 1. 

Hemicelluloses and Related Polysaccharides. HemiceUuloses [9034-32-6] are a large group of polysaccharides that are associated with ceUulose in the primary and secondary ceU waUs of aU higher plants, but otherwise have no relationship to ceUulose (2). They are also present in some other plants. 

Some hemicelluloses are partiaUy extractable with water, but they are usuaUy extracted with alkaline solutions foUowing removal of Upids and lignin. DeUgnifted plant material is termed, holoceUulose. Neutralization of the alkaline extract effects precipitation of the more linear and less acidic hemicelluloses, termed the hemiceUulose A [63100-39-0] fraction. The more acidic and more branched material, termed hemiceUulose B [63100-40-3], is precipitated with ethanol (70%). HemiceUulose B types type are usuaUy water-soluble after extraction. 

The two intermediates of commercial furan resins are furfural and furfuryl alcohol. Furfural occurs in the free state in many plants but is obtained commercially by degradation of hemicellulose constituents present in these plants. There are a number of cheap sources of furfural, and theoretical yields of over 20% (on a dry basis) may be obtained from both com cobs and oat husks. In practice yields of slightly more than half these theoretical figures may be obtained. In the USA furfural is produced in large quantities by digestion of com cobs with steam and sulphuric acid. The furfural is removed by steam distillation. 

In the past, research activities in the field of hemicellulose were aimed mainly at utilizing plant biomass by conversion into sugars, chemicals, fuel and as sources of heat energy. However, hemicelluloses, due to their structural varieties and diversity are also attractive as biopolymers, which can be utilized in their native or modified forms in various areas, including food and non-food applications. 

Xyloglucans are classified as gum when they are extractable with hot water from seed endosperm cell walls, such as the tamarind seed xyloglucan, and as hemicelluloses because they are alkali-extractable from the cell walls of vegetative plant tissues where they are closely associated with cellulose [2]. Also /3-glucans with mixed linkages appear under the name gum as well as hemicellulose in the literature. 

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. 

Xylan-type polysaccharides are the main hemicellulose components of secondary cell walls constituting about 20-30% of the biomass of dicotyl plants (hardwoods and herbaceous plants). In some tissues of monocotyl plants (grasses and cereals) xylans occur up to 50% [6j. Xylans are thus available in huge and replenishable amoimts as by-products from forestry, the agriculture, wood, and pulp and paper industries. Nowadays, xylans of some seaweed represent a novel biopolymer resource [4j. The diversity and complexity of xylans suggest that many useful by-products can be potentially produced and, therefore, these polysaccharides are considered as possible biopolymer raw materials for various exploitations. As a renewable resource, xylans are... 

Glucomannans (GM) and galactoglucomannans (GGM), common constituents of plant cell walls, are the major hemicellulosic components of the secondary cell walls of softwoods, whereas in the secondary cell walls of hardwoods they occur in minor amounts. They are suggested to be present together with xylan and fucogalactoxyloglucan in the primary cell walls of higher plants [192]. These polysaccharides were extensively studied in the 1960s [6,193]. 

The number of reports about hemicelluloses that have been covered by this review indicates the significantly increased importance of all types of hemicelluloses as plant constituents and isolated polymers during the last decade. Attention has been paid not only to known hemicelluloses but also to the primary structure, physicochemical, physical, and various functional properties of hemicelluloses isolated from hitherto uninvestigated plants. The efforts to exploit a variety of plant as potential sources of hemicelluloses were pointed out particularly for agricultural crops, wood wastes, as well as for by-products of pulp and rayon fiber technologies. Many studies were devoted to characterize seed-storage hemicelluloses from plants that have been traditionally applied in food and medicine of many underdeveloped countries to find substitutes for imported commercial food giuns. 

Plant litter consists mainly of sugars, cellulose, hemicellulose, lignin, waxes, and polyphe-... 

Kacurakova, M., Capek, P., Sasinkova, V., WeUner, N. Ebringerova, A. (2000). FT-IR study of plant cell wall model compounds pectic polysaccharides and hemicelluloses. Carbohydrate Polymers, Vol. 43,2, (October 2000), pp. (195-203), ISSN 0144-8617... 

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