Arabinoxylans

Due to the location and degree of integration in the different tissues of the grain, a part of AX is water-extractable, but the bulk can only be released by alkali solutions. Both the water- and alkali-extracted xylans consist of a family of related polymers differing in DS by a-Ara/ residues and substitution pat- 

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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. 

Primary examples. For example, arabinoxylans occur in different architectures, compositions, and charges. 

In contrast to AGX, the GAX consists of an arabinoxylan backbone, which contains about ten times fewer uronic acid side chains than a-L-Ara/ ones, and has some Xylp residues doubly substituted with these sugars. GAX are located in the non-endospermic tissues of cereal grains such as in wheat, corn, and rice bran. The degree and pattern of substitution of GAX appears to vary with the source from which they are extracted. These differences are reflected in the ratio of Ara to Xyl, the content of MeGlcA, and the presence... 

In contrast to the former Plantago CHX [55], the gel-forming CHX from psyllium (Plantago ovata) husks [54] was found to be a neutral, highly branched arabinoxylan with the (1 4)-j8-D-xylopyranose backbone substituted at position 2 with single Xylp units and at position 3 with the trisaccharide moiety (7). 

In a most recent paper [418] the preparation of corn fiber arabinoxylan esters by reaction of the polymer with C2-C4 anhydrides using methanesul-fonic acid as a catalyst is described. The water-insoluble derivatives with high molecular weight showed glass-transition temperatures from 61 to 138 °C, depending on the DS and substituent type. The products were thermally stable up to 200 °C. Above this temperature their stability rapidly decreased. 

Arabinoxylans with a substitution of the P-(l—>4)-D-xylopyranose backbone at position 2 or 3 with ArbF can be esterified partly with phenolic acids. This type is frequently found in the starchy endosperm and the outer layers of cereal grains. 

Piston F. Uauy C. Fu L. H. Langston J. Labavitch J. Dubcovsky J. (2010) Down-regulation of four putative arabinoxylan feruloyl transferase genes from family PF02458 reduces ester-linked ferulate content in rice cell walls / / Planta. N. 231. P. 677-691. 

This essay was written in an attempt to explain our overview of primary cell walls and to reach consensus on the nomenclature of primary cell wall polysaccharides. We present evidence supporting the hypothesis that cellulose, xyloglucan, arabinoxylan, homogalacturonan, RG-I, and RG-II are the six polysaccharides common to all primary cell walls of higher plants. In many cells, these six polysaccharides account for all or nearly all of the primary wall polysaccharides. Like the physically interacting proteins that constitute the electron transport machinery of mitochondria, the structures of the six patently ubiquitous polysaccharides of primary cell walls have been conserved during evolution. Indeed, we hypothesize that the common set of six structural polysaccharides of primary cell walls have been structurally... 

FAE was specific for esterified xylan-oligomers, but did not show selectivity towards a specific ester. This enzyme could release ferulic acid as well as acetyl groups from esterified arabinoxylans in the presence of an endoxylanase. 

Ferulic acid is the most abundant hydroxycinnamic acid in cereal grains. The content in wheat grain is approximately 800-2000 mg/100 g DW. It is found chiefly in the outer part of the grain, in the trans form, which is transformed into arabinoxylans and... 

DF content in the beverages listed in Table 8.4 ranges from 0.2 to 1.7 g/liter. These DFs contain an appreciable amount of associated phenolic compounds (from 0.05 to 0.89 g/liter). The main polyphenols associated with DF in wine are flavan-3-ols and benzoic acids (Saura-Calixto and Diaz-Rubio 2007), whereas in beer there would be flavonoids, followed by hydroxycinnamic acids linked to arabinoxylans (Dfaz-Rubio 2008). 

The only major accessory enzyme purified thus far for the xylanase was an a-(l,3)-L-arabinosidase with a molecular weight of 66,(XX) and isoelectric point of 4.1 (publication in preparation). The enzyme was not capable of acting on intact xylans. However, it acted on the end-products of arabinoxylan (but not glucuronoxylan) degradation by the xylanase, doubling the total extent of degradation. 

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