Barley cell-walls, arabinoxylans

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... 

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. 

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. 

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