Pentosan, cereal

Hoseney, R. C. Faubion, J. M. (1981). A mechanism for the oxidative gelation of wheat flour water-soluble pentosans. Cereal Chemistry, 58, 421-424. 

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. 

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. 

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). 

PENTOSAN. A complex carbohydrate (hemicellulose) present with the cellulose in many woody plant tissues, particularly cereal straws and brans, characterized by hydrolysis to give five-carbon-atom sugars (pentoses). Thus the pentosan xylan yields the sugar xylose (HOH,C CHOH CHOH CHOH CHO) that is dehydrated with sulfuric acid to yield furfural (C5H4O2). 

Neukom, H., and Markwalder, H. U. (1978). Oxidative gelation of wheat flour pentosans a new way of cross-linking polymers. Cereal Foods World 23 374-376. 

Furfural. 2-Fttraucarboxaldehyde 2-furaldehyde pyromucic aldehyde artificial oil of ants "furfuro] . C5-H402 mol wt 96.08. C 62-50%, H 4.19%, O 33.30%. Occurs in some essentia] oils. Prepd industrially from pentosans which are contained in cereal straws and brans. Laboratory prepn from corncobs It. Adams, V. Voorhees, Org. Syn. 

Furfural. The commerdal production of furfural depends on the conversion of the pentosans of oat hulls and other cereal products. Using lose as an example, the hydrolytic reaction may be represented as follows ... 

Ordinarily, oat huUs, which, have a relativdy high pentosan content and which are available as a by-product of cereal manufacture, are used. The... 

Hydrolyses of hemicelluloses yield mixtures of glucose, glucuronic acid, xylose, arabinose, galactose, galacturonic acid, mannose, and rhamnose. Some common polymers of pentoses, also known as pentosans, are xylan, galactan, araban, and others. Pentosans are found in large amounts (20-40%) in cereal straws and in brans. Large-scale industrial preparations of furfural, for instance, are based on these materials. 

Furfural is prepared industrially from pentosans which are contained in cereal strains and brans. It is obtained in the laboratory from corncobs. ... 

Geissmann, T., and H. Neukom A note on ferulic acid as a constituent of the water-insoluble pentosans of wheat flour. Cereal Chemistry 50, 414—416 (1973). 

Rye and other cereals can not form gluten. The baking quality of rye is due to pentosans and to some proteins which swell after acidification (cf. 15.4.2.2) and contribute to gas-holding properties. 

Both enzymes are widely distributed among cereals. The pH-activity curves of the enzymes from wheat show that at the normal pH values of a dough, about 6.3, catalase still has 40-50% and peroxidase less than 10% of its activity at the pH optimum (peroxidase pH 4.5 catalase pH 7.5). Therefore, it is unlikely that the oxidative cross-linkage of pentosans (Fig. 15.19), which is catalyzed by peroxidase, plays an essential role in dough. 

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). 

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. 

In foods heteroxylans are mainly present in cereals, found in thin endosperm cell walls, the aleurone layer and lignified bran cells. The endosperm cell walls of most cereals contain 60-70% arabinoxylans, with 20% in barley and 40% in rice. Glumes (husks) of wheat grains contain about 64% heteroxylans. Wheat grains contain on average 1.4-2.1% of heteroxylans, of which 0.8-1.5% represent water soluble pentosans. Rice grains contain 7-8% heteroxylans. 

Figueroa-Espinoza, M. C. Rouau, X. (1998). Oxidative cross-linking of pentosans by a fungal laccase and a horseradish peroxidase mechanism of linkage between feruloylated arabinoxylans. Cereal Chemistry, 75, 259-265. 

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