Barley arabinoxylans

Lee, R. C., Burton, R. A., Hrmova, M., and Fincher, G. B., Barley arabinoxylan arabinofuranohydrolases purification, characterization and determination of primary structures from cDNA clones. Biochem 72001, 356 (Pt 1), 181-9. 

Barley arabinoxylans are composed of D-xylopyranosyl (Xyl) units linked by (3-(l,4) bonds with single L-arab-inofuranosyl residues connected to the backbone of one or both of the a-(l,2) or a-(l,3) bonds [2, 3] Another unique... 

The presence of feruloyl and p-coumaroyl acids linked via L-arabinose residues has been verified in several studies of xylan (6-8). The amounts of these components, however, are rather small. Every 15th arabinose unit in barley straw arabinoxylan is estimated to be esterified with ferulic acid, and every 31st with p-coumaric acid (7). These hydroxycinnamic acids are bound to C-5 of the arabinose residue (7, 8). It has been suggested that oxidative dimerization of ferulic acid residues crosslinks the arabinoxylan chains and renders them insoluble as a result of the diferuloyl bridges (9). 

There have been few studies of polymer interconnections within the primary wall of monocots. An arabinoxylan from the primary wall of cultured, barley-aleurone cells,61 and a glucuronoarabinoxylan from maize-coleoptile primary-wall,200 have been shown to bind reversibly to cellulose in vitro, Because xylans are, quantitatively, the major component of monocot primary cell-walls, this interconnection is an important finding it is very likely to occur through multiple hydrogen-bonds, analogous to the interconnection between xyloglucan and cellulose in dicot cell-walls.56,57,59 It is also possible that heteroxylans participate in binding other cell-wall polymers to cellulose. 

In contrast to these findings, a glucuronoarabinoxylan isolated from oat coleoptiles did not bind to cellulose in vitro under reaction conditions that allowed other heteroxylans to bind.53 This oat heteroxylan had, however, a high percentage of arabinosyl side chains that would be likely to hinder binding sterically. A similar inability to bind to cellulose is exhibited by an arabinose-rich arabinoxylan isolated from cultured, barley-aleurone cell-walls.61... 

Phenolic acids, and especially ferulic acid, which is abundantly present in cereals, is found esterified to the polysaccharides present in primary and secondary cell walls of plants. Ferulic acid is the major phenolic acid occurring in the cell walls of monocotyledons and appears as cis and the more abundant trans isomers (reviewed in [Klepacka and Forna, 2006]). Ferulic acid is found in wheat, maize, rye, barley [Sun et al., 2001], oats, spinach, sugar beet, and water chesnuts [Clifford, 1999], generally esterified, and rarely as free form, such as in barley [Yu et al., 2001]. It is esterified in primary cell walls to arabinoxylans (Fig. 2.4) in the aleurone layer and pericarp [Clifford, 1999], as in spinach [Fry, 1982] or in wheat bran [Smith and Hartley, 1983], Ferulic acid can also be found esterified to other hydroxycinnamic acids such as in Mongolian medicinal plants where it is found as feruloylpodospermic acid, which is... 

Gas-liquid chromatography has provided supporting evidence for the identification of methylated sugars as cleavage products from the following, fully methylated materials pectic substances from lucerne, barley-husk and rye-flour arabinoxylans, a galactoglucomannan and an arabinogalac-... 

In contrast to the cell walls of parenchymatous tissues of dicotyledons, those of cereal grains (wheat, barley, etc.) contain very little, or no, pectic substances. The primary walls of most cereal grains have cellulose microfibrils, which are closely associated with glucomannan, and these fibrillar structures are embedded in an amorphous matrix of hemicelluloses, which consists mainly of arabinoxylans and/or P-D-glucans, some of which are cross-linked by phenolic esters and/or proteins (Selvendran,... 

Vigtor R.J., AngeUno S.A.G.F., Vosdragen A.G.J., Structural features of arabinoxylans from barley and malt cell wall material, J. Cereal ScL, 15, 1992, 213-222. 

Ferre H., Broberg A., Duus J.O., Thomsen K.K., A novel type of arabinoxylan arabinofuranosylhydrolase from germinated barley, Eur. J. Biochem., 267(22), 2000,6633-6641. 

Trypsin Enzymes from barley are released during the mashing stage of beer production Industrially produced barley enzymes Amylase, glucanases, proteases Betaglucanases and arabinoxylan-ases... 

In the class Monocotyledoneae, the composition of the hemicelluloses in the endosperm tissue varies greatly, e. g., wheat and rye contain mainly arabinoxylans (pentosans, cf. 15.2.4.2.1), while P-glucans (cf. 15.2.4.2.2) predominate in barley and oats. 

Soluble dietary fibre includes a certain proportion of hemi-ceUuloses. For example, about one third of cereal structural arabinoxylans are soluble. Also, one quarter to about one half of barley fl-glucans are soluble, and even a certain proportion of glucomannans and galactomannans of legumes are soluble. Other soluble polysaccharides are pectins, plant mucilages, seaweed polysaccharides, modified starches and modified celluloses (Table 4.21). 

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. 

Izydorczyk MS, Dexter JE. 2008. Barley [Beta]-Glucans and Arabinoxylans Molecular Structure, Physicochemical Properties, and Uses in Food Products - a Review. Food Research International 41(9) 850-868. 

---