Pentosan solubility

Somewhat analogous to these rice products is Oatrim, a material based on oat flour. It was developed at the Northern Laboratory of the USDA and is offered commercially by several firms. Oatrim contains 5% proteia, 5% P-glucan, 2% pentosans, and 83% maltodextrias. Unique properties are claimed based on the P-glucan component, and preparation of Oatrim is disclosed ia USDA pubHcations and patents. Briefly, oat flour is broken down by a-amylase, then the water-soluble component is dried and is the product of commerce, aimed at ground meat product usage. 

Certain cereal grains, especiaUy wheat and rye, contain hemicelluloselike arabinoxylans [9040-27-1], commonly caUed pentosans. Wheat flour pentosans are divided into two types water-soluble and water-insoluble arabinoxylans, which respectively constitute - 1.1 1.6% and 0.4—0.7% of the total flour. These polysaccharides have functional roles in dough development and baking performance. The water-soluble wheat-flour arabinoxylans consist of a (1 — 4)-linked chain of P-D-xylopyranosyl units substituted at 0-2 and/or 0-3 with single-unit a-L-arabinofuranosyl units. Preparations from each source consist of a family of molecules of various molecular weights and xyl ara ratios. 

However, fine grinding of iasoluble dietary fiber such as bran reduces WHC. In general, branched polysaccharides are more soluble than are linear polysaccharides because close packing of molecular chains is precluded. WHC is strongly kifluenced by the pentosan components of cell-waU dietary fiber and varies with the stmcture and source of these hemiceUuloses. 

The support for a chemical linkage between cellulose and lignin in wood, presented by Hibbert and co-workers (90), is based on their treatment of oak wood with acetic anhydride, glacial acetic acid and catalytic amounts of sulfuric acid. A fraction soluble in dioxane was found to have, after several precipitations, the same composition of lignin, cellulose and pentosan as that of the wood itself. 

Dried Gluten. This material is sold as vital wheat gluten, it is produced by a scaled up version of the process for producing wet gluten for flour testing. A flour and water dough is made and then washed to remove the starch, the soluble proteins and the pentosan-based gum fraction. This latter fraction is an example of a non-starch carbohydrate. 

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. 

Xylan has the general properties of insolubility in water, solubility in alkaline solutions, ease of acid hydrolysis, high negative optical rotation, and non-reducing action toward Fehling s solution. It can be placed in three general polysaccharide classes (1) pentosan, (2) glycan, and (3) hemicellulose. It is classed as a pentosan because it is principally a polymer of a pentose. It is by far the most abundant pentosan. 

Usually it is considered that xylan has been effectively removed if the extracted residue compares in composition to a-cellulose. Yet, even a-cellulose contains small amounts of xylan as well as other hemicelluloses such as mannan.67 69 Beta and 7-cellulose are mixtures which contain pentosans along with other alkali-soluble extractives.1M0... 

Both D-glucuronic acid and/or its 4-O-methyl ether and arabinose are also present in cereal xylans (4). Endospermic arabinoxylans of annual plants, often referred to as pentosans, are because of their branched structures more soluble in water and dilute alkali than xylans of lignocellulosic materials. They also have at least one, or even two, substituents per xylose residue (5). 

The final purification is designed chiefly to remove pentosans, as these undergo nitration with difficulty to yield products of low nitrogen content that are insoluble or only partly soluble in organic solvents. Hence the presence of pentosans can... 

The ratio acid cellulose was 60. The nitration was carried out for 1 hr at 15-18°C. From the values obtained the deleterious effect of pentosans is noticeable since the presence of these compounds reduces the yield and the solubility of the product. The adverse effect of a high percentage of pentosans is less evident when only lower... 

The other carbohydrates in cane juice are the soluble polysaccharides vaguely classified under the terms "hemi-celluloses, soluble gums and pectins. It is possible that some of these polysaccharides may enter the juice during the milling of the cane as the plant cell structure is destroyed. A gummy product has been isolated from cane fiber by alkali extraction followed by alcohol precipitation. Acid hydrolysis of this substance yielded crystalline D-xylose and L-arabinose.10 Such gums in Trinidad cane juices were isolated by alcohol precipitation at suitable hydrogen ion concentration and assayed for pentose content by the Tollens 2-fural-dehyde assay the results showed an apparent pentosan content of 0.04-0.07%u of the Brix solids. 

The A-starch slurry from the centrifugal decanter is screened and then refined either with hydrocyclones or with separators and decanters. Purification and concentration of A-starch is accomplished in multistage hydrocyclones, or the A-starch slurry is separated into A and B fractions in a nozzle-type centrifuge and the A-starch fraction is finally refined in a centrifugal decanter. The B-starch stream is passed through vibrating screens and concentrated in a decanter. Pentosans and other solubles are concentrated and either dried or co-fermented with the B-starch for ethanol production. 

B. H. Howard, Hydrolysis of the soluble pentosans of wheat flour and Rhodymenia palmata by ruminal micro-organisms, Biochem. J., 67 (1957) 643—651. 

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. 

The procedure for determining the methyl pentosan content of the raw material is based on the fact, discovered by Schorger [114], that methyl furfural phloroglucide is soluble in hot ethanol while furfural phloroglucide is not, so that the two can be separated. 

In comparison with fungal amylase, fungal hemicellulase is more functional. Hemi-cellulase is a complex mixture of enzymes. It hydrolyses water-insoluble hemicellu-lose into water-soluble pentosan and, as a consequence, has a great impact on dough water management. 

In several cases, separation of acidic xylans from neutral glucomannans has been achieved by way of their acetates, by a method originally suggested by Perlin. As mentioned earlier (see Part I, p. 295), the acetates of acidic xylans are seldom readily soluble in chloroform. On the other hand, acetylated hexosans dissolve readily. When a chloroform solution of a glucuronoxylan acetate and a glucomannan acetate is shaken with water, an emulsion is formed which contains the pentosan acetate while the hexosan acetate remains in the chloroform. This method has been successfully applied by other workers, but it is somewhat time-consuming. 

The main direction of research now appears to be toward the utilization of wood by-products. Wood generally contains from 50-60% cellulose, 20-30% lignin, 10-20% pentosans, 0-7% mannans and some acetyl linkages (usually 0.5-2% acetic acid) (48). This wide assortment of carbohydrates is of interest to ruminant nutritionists for at least three reasons. Ruminants need a source of readily available energy, usually obtained as hexoses derived from soluble carbohydrates. Most forages contain pentosans or hemicelluloses, but no reliable concentrated pure source of these materials is available and until recently it was not possible to obtain enough to evaluate the utility of these products in defined rations. Finally, the possibility of producing polymers from feed material is attractive. 

Interactions of aqueous electrolytes with nonionic polysaccharides play an essential role in Investigations of plant cell wall polysaccharides, where Isolation and fractionation procedures are commonly based on different degrees of solubility in particular electrolytes. This is especially true of the beta-1,4-linked pentosans and hexosans which are the primary backbone structures of most of the cell wall polysaccharides not Infrequently solubility is the basis of identification as well. The beta-1,4-linked hexosans are a special subset which, because of constraints on the freedom of rotation about the bonds of the glycosidic linkage, tend to be less soluble than the pentosans or the hexosans with less constrained linkages. 

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