Wheat arabinoxylans

Of the related polysaccharides mentioned earlier (see p. 267), only arabinoxylans have been examined in any detail by enzymic methods. Goldschmid and Perlin153 studied the fine structure of wheat arabinoxylan by using the /3-D-xylanase from Streptomyces QMB 814. Their results indicated that arabinoxylan molecules are mainly constituted of highly branched regions in which isolated and paired L-arabinosyl (A) branches are separated by single D-xylosyl (X) residues, as shown in 12, but that, at unequal intervals (averaging... 

Figueroa-Espinoza, M.C., Morel, M.H., Surget, A., Rouau, X. 1999. Oxidative cross-linking of wheat arabinoxylans by manganese peroxidase. Comparison with laccase and horseradish peroxidase. Effect of cysteine and tyrosine gelation. J Sci Food Agric 79 460-463. 

XOS are manufactured by enzymatic hydrolysis of xylan from corn cobs, oat spelt xylan or wheat arabinoxylan [257]. Xylan, a principle t)q)e of hemicellulose exists as a linear polymer of -D-xylopyranosyl units linked by 1 4 glycosidic bonds. Depending on the origin, different substituents such as arabinfuranosyl, 4-0-methylglucuronosyl and acetyl groups are present. Typical raw materials for XOS production include hardwoods, com cobs, straws. 

In its attack on L-arabinan, the A. niger enzyme10,85 was found to hydrolyze the substrate rapidly to the extent of 30% thereafter, attack was slow. This initial, rapid hydrolysis of L-arabinan corresponds to the favored attack on the a-L-(l — 3)-linked L-arabinofuranosyl residues, leaving a mainly linear (1 — 5)-a-L-arabinan which was slowly, and eventually, completely, hydrolyzed to L-arabinose. Tagawa and Kaji64 utilized this unique property of their enzyme preparation to prepare from the parent L-arabinan a linear (1 — 5)-L-arabinan which was subsequently purified and characterized. In a similar way, wheat arabinoxylan yielded a predominantly linear (1 — 4)-/3-D-xylan. 

Barker, D.K., Wilde, P.J., and Clark, D.C. Enhancement of protein foam stability by formation of wheat arabinoxylan-protein crosslinks. Cereal Chem., 493, 1998. 

A measure of the numerical sequences of residues in a wheat arabinoxylan that accommodate enzymolysis by a Streptomyces xylanase, is given by the pattern of periodate oxidation of the hydrolysis fragments. For the observed release of xylobiose, for example, the sequence required is at least four consecutive D-xylopyranose residues having no L-arabinofuranosyl branches. Polysaccharides from soil contain considerable proportions of (1 4)-linked glucose and xylose residues that resist periodate oxidation, for both chemical and physical reasons that remain unsolved. ... 

Hoffman RA, van Wijk J, Leeflang BR, Kamerling JP, Altona C, Vliegenthart JFG (1992) Conformational analysis of the a-L-arabinofuranosides present in wheat arabinoxylans from proton-proton coupling cmrstants. J Am Chtan Soc 114 3710-3714... 

Sorensen H.R., Meyer A.S., Pedersen S., Enzymatic hydrolysis of water-soluble wheat arabinoxylan. 1. Synergy between alpha-L-arabinofuranosidases, endo-1, 4-beta-xylanases, and beta-xylosidase activities, Biotechnol. Bioeng., 81(6), 2003, 726-731. 

Sprensen HR, Pedersen S, Meyer AS. (2007). Synergistic enzyme mechanisms and effects of sequential enzyme additions on degradation of water insoluble wheat arabinoxylan. Enzyme Microb Technol, 40(4), 908-918. 

Hughes SA, Shewry PR, Li L, Gibson GR, Sanz ML, Rastall RA. In vitro fermentation by human fecal microflora of wheat arabinoxylans. 

Virkki, L Maina, H.N., Johansson, L. and Tenkanen, M. (2008) New enzyme-based method for analysis of water-soluble wheat arabinoxylans. Carbohydr. Res., 343, 521-529. 

Arabinoxylans of various cereals differ not only in how the xylan chains are substituted, but also have different arabinose contents or ratios of these two sugars. The ratio of arabinose and xylose in wheat arabinoxylans varies from 0.50 to 0.71 and in less substituted rye arabinoxylans it ranges from 0.48 to 0.55. D-Glucuronic acid and its 4-0-methyl ether are found mainly in... 

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. 

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... 

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... 

Feruloyl esterase activity was first detected in culture filtrates of Strepto-myces olivochromogenes (49), and has thereafter also been reported for some hemicellulolytic fungi (Table III). A partially purified feruloyl esterase from S. commune liberated hardly any ferulic acid without the presence of xylanase (65). Very recently a feruloyl esterase was purified from Aspergillus oryzae (Tenkanen, M. Schuseil, J. Puls, J. Poutanen, K., /. Biotechnol, in press). The enzyme is an acidic monomeric protein having an isoelectric point of 3.6 and a molecular weight of 30 kDa. It has wide substrate specificity, liberating ferulic, p-coumaric, and acetic acids from steam-extracted wheat straw arabinoxylan. 

Synergism between a-arabinosidase, xylanase and j8-xylosidase has been demonstrated in the hydrolysis of wheat straw arabinoxylan with purified enzymes of T, reesei (71). > en only xylanase and )8-xylosidase were used in the hydrolysis, the xylose yield was only 66% of that produced by the whole culture filtrate at the same activity levels of these two enzymes, and no arabinose was produced. Addition of a-arabinosidase increased the yields of both xylose and arabinose. Enhanced hydrolytic action of hemicellulolytic or pectinolytic enzymes in the hydrolysis of alfalfa cell wall polymers by addition of Ruminococcus albus a-arabinosidase has also been reported (37). 

Hydrolysis Experiments. The substrate in the hydrolysis experiments included alkali-extracted beechwood 4-O-methylglucuronoxylan, DMSO-extracted acetylated beechwood 4-O-methylglucuronoxylan, alkali-extracted wheat straw arabinoxylan and acetylated or deacetylated xylo-oligomers from steaming of birchwood (24). Deacetylation was carried out by incubating the freeze-dried xylo-oligomers in ammonia vapor overnight. Substrate concentration was 10 gl— 1, temperature 45° and hydrolysis time 24... 

Table II. The effect of a-arabinosidase on the hydrolysis of wheat straw arabinoxylan. Substrate concentration 10 gl-1, initial pH 4, temperature 45° C, hydrolysis time 24 h...

Figure 2. Hydrolysis products of beechwood O-acetylglucuronoxylan (Fig. 2a), beechwood glucuronoxylan (Fig. 2b), and wheat straw arabinoxylan (Fig. 2c), as analyzed by gel permeation chromatography. The hydrolysis was carried out at pH 5 at 45°C for 24 h using 10.000 nkat of the 20 kDa xylanase of T. reesei. X = xylose X2 = xylobiose Xmga — 4-O-methyl-glucuronosyl substituted xylo-oligosaccharides X = xylo-oligosaccharides DP > 20.

Xylanase Arabinoxylans of wheat and rye Improved litter quality Improved feed utilization... 

The minor content of impurities found in the starch slurry are connected to the starch granules themselves. To facilitate the purification of the starch during filtration, cellulases, pentosanases, glucanases, proteases, and pectinases are sometimes used. Wheat starch is known to form precipitates or hazes that are difficult to filter. Arabinoxylan, pentosanes, andlysophospholipids are claimed to be responsible for this problem (73). 

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... 

Xylanase added to a wheat-based diet helps to break down arabinoxylan, an NSP, improving the digestibility of carbohydrate and enhancing fat, protein and starch digestion. 

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