Pentosans formation

The estimation of furfural potential of various raw materials is best done by the AO AC method (1). Although Hquid chromatographic methods are now available for the estimation of polymeric pentosans, results do not always correlate well with furfural formation. 

These observations have a bearing also on certain claims37 which have been made concerning a supposed increase in the pentosan content when pectin is heated in alkaline solution. It is obvious that any increase in the proportion of pentosan in the product cannot be due to decarboxylation of the pectic acid molecule with the formation of the araban. The... 

A great deal of work is reported in the literature concerning the formation of lignin directly from cellulose or pentosans. Phillips (92), (93), on the basis of his work on annual plants, opposed this theory. According to him, lignin is produced in the plant directly from glucose or sucrose. 

Rye Proteins. While rye is the only European cereal able to completely replace wheat in bread, rye protein is not as effective as wheat protein. One reason for this is that as much as 80% of the protein in a rye sour dough is soluble compared with 10% of soluble protein in a wheat dough. One factor that inhibits the formation of a gluten-like complex is the 4-7% of pentosans present, which bind water and raise the viscosity of the dough. The crumb structure is then formed from the pentosans in combination with the starch. 

Didehydroferulic Acid 23 Formation. It should be noted that no direct evidence has ever been obtained in vivo to prove that didehydroferulic acid 23 is formed via free radical coupling reactions. This mechanism is assumed, since in vitro incubation of ferulic acid 1 and wheat pentosan, with... 

From this type of schematic representation it would be expected that a more highly branched xylan chain would give more potential for reaction of the arabinose residues, either through crosslink formation or by Maillard-type reactions. Indirect evidence supporting this concept can be derived from pentosan analysis of the hemicellulose fraction of grasses and legumes. 

The pyrolysis oil collected between 200 to 275 C in the second step was 18.14 % by wt. on an anhydrous wood basis and corresponded to the hemicelluloses degradation . In general, hemicelluloses decompose to yield furans and its derivatives as well as a series of aliphatic carboxylic acids. Hardwoods are composed of pentosan-based hemicelluloses, while hexosan-based hemicelluloses are found in softwoods. Hardwood produces more low molecular weight carboxylic acids and furans than softwood upon decomposition . In contrast, hardwood contains a lower quantity of fatty acids than softwood. Cl - C6 carboxylic acids, fatty acids (e.g. Cia), fiiran and derivatives were identified in this fraction. In the second pyrolysis step, a little rearrangement of the lignin polymer occurred which was based on the formation of small amount of phenolic compounds 0,395 % by wt., anhydrous wood basis). The main components of this fraction are listed in Table 2. Betulin and lupeol were abundant in this fraction. Furthermore, levoglucosan which has been reported earlier as a major compound in the cellulose-derived pyrolysis oils, was identified in the second... 

The rate of pentose formation from pentosan is proportional to the pentosan concentration, but is diminished by the sequence reaction of pentose to furfural, so that... 

With the sealed ampoule process used for their kinetic studies, Root, Saeman, Harris, and Neill [20] achieved fiirfiiral yields well in excess of 70 % at temperatures above 220 °C, whereas industrial furfural processes, operating at lower temperatures and featuring a continuous removal of the furfural by steam stripping, have typical yields below 60 %. By contrast, in analytical chemistry, at a proven yield of 100 % [21], the formation of furfural from xylose or pentosan is routinely used for the quantitative determination of these substances. It is of great importance to elaborate the reasons for this yield paradox . 

The explanation for the formation of 5-methyl furfural and furyl methyl ketone, which are isomers, lies in the fact that all raw materials used for the manufacture of furfural contain some methyl pentosan. As the furfural manufacturers are not in a habit to measure the methyl pentosan content of their raw material, it is instructive to look at the pentosan and methyl pentosan contents of various woods as published by Hagglund [42]. These data are compiled in Table 2. The methyl pentosan values were measured by a procedure due to Schorger [43], which is based on the fact that methyl furfural phloroglucide is soluble in hot ethanol while furfural phloroglucide is not. 

Wood contains from 8 to 10 per cent of a gum which is a mixture of complex carbohydrates. Wood gum yields xylose on hydrolysis and, like other substances which contain pentosans, is. converted into furfural on boiling with hydrochloric acid. The formation of furfural, it will be recalled, is a test for a pentose (365). 

Carbohydrates constitute the main constituents of plants, with.cellulose the most abundant. In addition, are the various hemicelluloses or polysaccharides, pentosans and polyuronides. Most of these substances, especially cellulose, are readily attacked by many species of soil microorganisms. The result is that the carbohydrate content of humus is very different from that of the plant residues from which most of the humus is derived (Gupta, 1962 Gupta et al, 1963 Gupta and Sowden, 1964). Humus usually contains little cellulose but does contain hemicelluloses and polyuronides. These substances are in part the residues of the original plant materials but most of them are the synthesized gums, slimes and cell walls of the microorganisms that are responsible for decomposition and the formation of humus. 

The degradation of proteoglycan by an elastase-enriched neutral protease preparation from leukocytes has been shown to be inhibited by pentosan polysulphate, an anti-inflammatory agent, presumably by formation of a complex between the drug and the proteoglycan. ... 

The aldobiouronic acids liberate carbon dioxide and form furfural in a manner similar to the uronic acids. With polysaccharide materials, the formation of carbon dioxide is considered very strong evidence for the presence of uronic acids. The evidence for a biological formation of pentosan material by the decarboxylation of uronic acid groupings is very weak, however, for some polyuronide materials contain both arabofuranose and galactopyranose units (see Chapter XII). 

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