Hemicellulosic Materials and of Pure Hemicelluloses

As used in this Chapter, the term non-endospermic hemicellulose refers to hemicelluloses from aerial tissues and organs (bran, cob, hull, husk, leaves, stems, and other parts), but excludes those from root tissues. The hemicelluloses associated with cereal starches and flours are collectively termed endospermic hemicelluloses. 

Non-endospermic tissues of grasses are often subjected not only to delignification but to other treatments before the intentional extraction of hemicellulosic materials. It is not always clear that a useful purpose is served by some of these treatments, or that they do, or only do, what is wanted. The fact that a procedure has often been used does not alone justify its routine adoption or retention. As mentioned, enzymes may be inactivated by hot, aqueous alcohol78,79 in which oligo- 

The various procedures used prior to the intentional extraction of hemicelluloses may affect quantitative or structural conclusions about the hemicelluloses as they occur in Nature. It must be uncertain whether structural features are destroyed or modified by the use of 

The hemicellulosic materials extracted by alkali are, in part, precipitated on neutralization or mild acidification, and, in further part, by the subsequent addition of an excess of acetone or ethanol.29 Under these conditions, part of the hemicellulosic material remains in solution, and is commonly not recovered. An oat-leaf holocellulose was treated with aqueous acid, and the precipitated hemicelluloses were recovered after the addition of an excess of acetone. The solvents were removed from the remaining solution and, after dissolving the 

Studies of fractionated materials have led to much structural information on molecules in those parts of the populations of hemicellulosic molecules recovered by the most commonly used procedures. 

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