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Carbohydrates Hemicelluloses, Polysaccharides

Occurrence. D-Xylose (10) is present in widely abundant polysaccharides of plant tissues. Xylan is the main carbohydrate found in the hemicellulosic fraction, and accounts for one third of all renewable organic carbon available on earth. The structure and composition of xylans are variable, from linear (3-(l->4)-linked xylose chains to highly branched heteropolysaccharides. The branches may involve short oligosaccharides, usually of L-arabinofuranosyl units. Xyloglucans are also important hemicellulose polysaccharides consisting of a backbone of ( I — 4)-(i-D-glucopyranosyl residues heavily substituted with a-D-Xylp. Other monosaccharides may also be present.44... [Pg.16]

Since starch is the most important and widespread reserve carbohydrate in seeds we will begin by surveying the metabolic reactions through which this polysaccharide is mobilized into a form available for the embryo. Details of the breakdown of other stored carbohydrates (hemicellulose, galactomannan, oligosaccharides) are discussed in the appropriate sections. [Pg.177]

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... [Pg.81]

The carbohydrates in rice bran are made up of the cell wall components such as polysaccharides, oligosaccharides, hemicelluloses, starch and some sugars. The health benefits of rice bran polysaccharides and hemicelluloses are discussed under phytochemicals of rice bran below. It is lactose-free and gluten-free. The water-soluble non-starchy polysaccharides, oligosaccharides and hemicelluloses are concentrated in the water-soluble fraction of rice... [Pg.352]

The primary walls of growing plant cells are composed of 90% carbohydrate and 10% protein (51). Carbohydrate in the primary wall is present predominantly as cellulose, hemicellulose, and pectin. The pectic polysaccharides, are defined as a group of cell wall polymers containing a-l,4-linked D-galactosyluronic acid residues (62,76). Pectic polysaccharides are a major component of the primary cell waU of dicots (22-35%), arc abundant in gymnosperms and non-graminaceous monocots, and are present in reduced amounts (-10%) in the primary walls of the graminaceae (27,62). [Pg.110]

We should note, also, that the lignin in the S2 layers is chemically bonded to the polysaccharide moiety (87-92). Such bonds occur not only in wood but may be formed during chemical pulping (93,94). Even if the lignin-carbohydrate bonds are restricted to the hemicelluloses (95), the regularity of these chain molecules will probably impose some non-randomness on the lignin structure. [Pg.13]

The present utilization of carbohydrates as a feedstock for the chemical industry is modest, when considering their ready availability, low cost and huge potential [92], The bulk of the annually renewable carbohydrate biomass consists of polysaccharides, but their non-food utilization is still modest. The low-molecular-weight carbohydrates, that is, the constituent units of these polysaccharides, are potential raw materials for several commodity chemicals in fact, glucose (available from cornstarch, bagasse, molasses, wood), fructose (inulin), xylose (hemicelluloses) or the disaccharide sucrose (world production 140 Mtons year-1) are inexpensive and available on a scale of several ten thousands. [Pg.316]

The polysaccharides cellulose and hemicellulose are two major components of lignocellulosic biomass and form an abundant, non-edible and renewable source of carbohydrates. Other sources include starch, chitin, inulin and smaller... [Pg.78]

Carbohydrates would be the predominant raw materials for future biorefineries. The major polysaccharides found in nature are cellulose, hemicellulose and starch (see Chapter 1). These molecules would be mainly utilised after they are broken down to their respective monomers via enzymatic hydrolysis, thermochemical degradation or a combination of these two. Cellulose and hemicellulose, together with lignin, constitute the main structural components of biomass. Starch is the major constituent of cereal crops. This section would focus on the potential utilisation of carbohydrates and lignocellulosic biomass for chemical production. [Pg.79]

Polysaccharides are the most abundant constituents of living matter. They are in principle built up in the same manner as oligosaccharides. The chain molecules can be either linear or branched, a fact that markedly affects the physical properties of the polysaccharides. The carbohydrate material in plants is largely composed of cellulose and hemicelluloses. Chapter 3 deals with their structure and properties. [Pg.37]

As I have already indicated, the polymeric carbohydrate materials available from natural sources include gums, starch and dextrins, cellulose, hemicellulose, chitin, and bacterial polysaccharides. [Pg.269]

The other noticeable product of this era was a steady stream of publications, mainly to the Journal of the Chemical Society, but also to the Biochemical Journal, to Chemistry and Industry, and later, to Carbohydrate Research. The atmosphere of this period is conveyed in several review lectures given by Hirst for example, the fourteenth Pedler lecture to the Chemical Society (1955) on Some Problems in the Chemistry of the Hemicelluloses, the Presidential Addresses to the Chemical Society (1957 and 1958) on Some Aspects ofthe Chemistry of the Fructosans and Polysaccharides of the Marine Algae, respectively, on Plant Gums, at the IVth International Congress of Biochemistry, Vienna (1958), and the Bakerian Lecture to the Royal Society (1959) on Molecular Structure in the Polysaccharide Group. These lectures were delivered with a quiet authority, and the published manuscripts show meticulous attention to detail. [Pg.8]

The Chapter by Wilkie (Aberdeen) on the hemicelluloses of the Gramineae serves to illustrate that not all areas of complex carbohydrates are yet amenable to neat and clear-cut structural interpretations as a result of modern technology. The article emphasizes the need for continued caution in attribution of precise structures to this enigmatic class of polysaccharides, and final answers can not yet be written on their structures and roles. [Pg.386]


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Carbohydrates polysaccharides

Hemicellulose

Hemicelluloses

Hemicelluloses polysaccharides

Polysaccharides hemicellulose

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