Pentosans

Properties of Pentosans (SECTIONS 365, 382, 656).— (a) Tests for lignin.—Dissolve a few drops of aniline in a few drops of dilute hydrochloric acid, and dilute with 5 cc. of water. Pour one-half of the solution onto a piece of paper made from wood-pulp (newspaper) and one-half onto a paper made from linen. Repeat the tests using a solution of phloroglucinol in dilute hydrochloric acid. 

Cereals also contain polysaccharides other than starch. In endosperm cells their content is much less than that of starch (cf. Table 15.29). They include pentosans, cellulose, 3-glucans and glu-cofructans. These polysaccharides are primarily constituents of cell walls, and are more abundant in the outer portions than the inner portions of the kernel. Therefore, their content in flour increases as the degree of fineness increases (cf. rye as an example in Table 15.36). 

From a nutritional and physiological viewpoint, soluble and insoluble polysaccharides other than starch and lignin (cf. 18.1.2.5.1) are also called dietary fiber. The most important fiber sources are cereals and legumes, while their content in fmits and vegetables is relatively low. 

The pentosan content of cereals varies. Rye flour is exceptionally rich (6-8%) in comparison to wheat flour (1.5-2.5%). A portion of pentosans, 25-33% in wheat and 15-25% in rye, is water-soluble. 

The Ws-AX cause up to 25% of the water binding in dough. They increase the viscosity and, consequently, the stability of the gas bubbles. In contrast, the action of Wi-AX is considered to be unfavourable. They form physical barriers against the gluten and destabilize the gas bubbles. 

Accordingly, the baking result is positively influenced by endoxylanases which preferentially hydrolyze Wi-AX. Since inhibitors are present in wheat which inhibit the activity of added endoxylanases, attempts are being made with the help of molecular engineering techniques to produce microbial enzymes which do not react with these inhibitors. 

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The pentosan polysaccharides, xylan and arabinan, commonly known as hemiceUulose, are the principal precursors of furfural and are always found together with lignin and cellulose in plant materials. 

Furfural is commercially produced in batch or continuous digesters (37) where the pentosans are first hydroly2ed to pentoses (primarily xylose (12), which are then subsequendy cyclodehydrated to furfural ... 

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. 

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 minor content of impurities found ia the starch slurry are connected to the starch granules themselves. To faciUtate the purification of the starch duriag filtration, ceUulases, pentosanases, glucanases, proteases, and pectinases are sometimes used. Wheat starch is known to form precipitates or hazes that are difficult to filter. Arabiaoxylan, pentosanes, andlysophosphoHpids are claimed to be responsible for this problem (73). 

A pentosanase that works on the gluten—pentosan fraction of flour results in easier dough-handling and improved cmmb stmcture. Pentosanases... 

The German ending -an should be translated -ane if it is the name of a hydrocarbon (or parent heterocyclic compound) which is fully saturated otherwise, -an. Examples methane, menthane, tolan, furan, pentosan. 

Pentosan polysulfate Inhibits heparin-binding growth factors... 

Xylan sulphates, known also as pentosan polysulphates (PPS), are permanently studied with regard to their biological activities [3,419-422]. Usually, sulphuric acid, sulphur trioxide, or chlorsulphonic acid are employed as sul-phating agents alone or in combination with alcohols, amines or chlorinated hydrocarbons as reaction media [423]. 

Polysaccharides are condensation products of more than ten monosaccharide units examples are the starches and dextrins, which may be linear or branched polymers. Polysaccharides are sometimes classified as hexosans or pentosans, depending upon the identity of the constituent monosaccharides. 

Maffrand JP, Herbert JM, Bernat A, Defreyn G, Delebassee D, Savi P, Pinot JJ, Sampol J. Experimental and clinical pharmacology of pentosan polysulphate. Semin Thrombosis Haemostasis 1991 17 (Suppl. 2) 186-198. 

The concept of extractive reaction, which was conceived over 40 years ago, has connections with acid hydrolysis of pentosans in an aqueous medium to give furfural, which readily polymerizes in the presence of an acid. The use of a water-immiscible solvent, such as tetralin allows the labile furfural to be extracted and thus prevents polymerization, increases the yield, and improves the recovery procedures. In the recent past an interesting and useful method has been suggested by Rivalier et al. (1995) for acid-catalysed dehydration of hexoses to 5-hydroxy methyl furfural. Here, a new solid-liquid-liquid extractor reactor has been suggested with zeolites in protonic form like H-Y-faujasite, H-mordenite, H-beta, and H-ZSM-5, in suspension in the aqueous phase and with simultaneous extraction of the intermediate product with a solvent, like methyl Aobutyl ketone, circulating countercurrently. 

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... 

The well-known acid-catalyzed conversion of sugars into furan derivatives obviously consists of a complex sequence of reactions, and the industrial heterophasic conversion of pentosans in plant tissues has been discussed in detail.11 The reactions themselves are still not well understood, although xylose and glucuronic acid in deuterium oxide afford 2-furaldehyde without uptake of isotope thus limiting the mechanistic possibilities to those not permitting reversible enolization.12 The bacterial sugar streptose yields... 

Among other polyions Meyerhoff s group demonstrated successful detection of pentosan polysulfate (PPS) [45], an anti-osteoarthritis drug, in plasma and polyanions with high phosphate content, including polyphosphates and nucleic acids in saline solutions [46],... 

N. Durust and M.E. Meyerhoff, Determination of pentosan polysulfate and its binding to polycationic species using polyion-sensitive membrane electrodes. Arm Chim. Acta 432, 253-260 (2001). 

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. 

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. 

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. 

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