Wheat straw, xylan

Potential resources of xylans are by-products produced in forestry and the pulp and paper industries (forest chips, wood meal and shavings), where GX and AGX comprise 25-35% of the biomass as well as annual crops (straw, stalks, husk, hulls, bran, etc.), which consist of 25-50% AX, AGX, GAX, and CHX [4]. New results were reported for xylans isolated from flax fiber [16,68], abaca fiber [69], wheat straw [70,71], sugar beet pulp [21,72], sugarcane bagasse [73], rice straw [74], wheat bran [35,75], and jute bast fiber [18]. Recently, about 39% hemicelluloses were extracted from vetiver grasses [76]. 

Aqueous alkaline extraction of wood was employed by Poumarede and Figuier48 in 1846 for the removal of a substance called wood gum. Similar very crude xylan or hemicellulose preparations were made by other workers of the early period. Extractions were made not only from wood sawdust, but from annual plant materials such as wheat straw, corn cob, etc.49-66... 

Other workers140 have also examined the products derived by hydrolysis of periodate-oxidized xylan. Both wheat straw and com cob xylan, after oxidation and hydrolysis, yield small amounts of L-arabinose and D-xylose. These sugars are obtained even after the xylans have been subjected to extended periods of oxidation. It is concluded that the D-xylose constituted branch points in the xylan. Likewise, the L-arabi-nose molecules must not have been terminal units in a xylan chain but must have been either interior units in the xylan molecule or have constituted an araban-like polysaccharide which is in combination or admixture with the xylan polysaccharide. 

Wheat straw (1 -3)-D-Xylp (1 — 2)-D-Xylp (Me) some branched xylan chains 39... 

Xylan and Glucan Conversions for Upgrading of Wheat Straw Stems Using P. ostreatus at 23.0-149 mg/g of Stems and Moisture Contents of 1.10-2.24 g of H20/g of Stems"... 

Although non-endospermic, hemicellulosic materials have often been reported to yield glucose on hydrolysis, there is little evidence of the presence of glucosyl residues in xylans. Non-cellulosic glucose occurs mainly, or exclusively, in /J-D-glucans (described later in this Section). 2,6-Di-O-methylglucose was obtained on methylation and hydrolysis of the xylans of wheat straw and com cob,132 and its presence is indicative of doubly linked glucose residues attached in some way to these xylans.132... 

Xylan from wood has received somewhat less attention from carbohydrate chemists than has the xylan from such rich sources as wheat straw, corn cobs, and esparto grass. However, specific optical rotations of the xylans obtained from the aforementioned sources are of the same general order of magnitude as those of some xylans obtained from wood. Yundt crystallized xylans from paper birch and from barley straw as sphero-crystals, and compared their properties (see Table VII). 

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