Beechwood hemicelluloses from

The foregoing observations confirm the conclusions derived from former experiments with beechwood holocellulose (10) (1) A partial degradation of the hemicelluloses is imperative before the cellulose fibrils can be attacked. (2) The hemicelluloses seem to be deposited between the cellulose fibrils or even to be encrusting them. (3) The enzymatic hydrolysis of the cellulose is governed by the porosity of the tissue (enzyme diffusion), the impediment of the hemicelluloses, and the properties of the cellulose (e.g., crystallinity). 

The current observations confirm previous studies on beechwood and sprucewood holocellulose (7,10,19). The attack of the hemicellulose proceeds from the primary wall/Si as well as from the tertiary wall into S2 the pit chambers constitute preferred paths of enzyme diffusion into the walls. Also, substances of the middle lamella, especially in the cell corners, are removed by the xylanase and the mannanase treatments. Parallel to the removal of hemicelluloses, the fibrillar structure of the cellulose and its lamellar arrangement in transections of cell walls became obvious. In samples treated with cellulases, the cellulose fibrils were often completely hydrolyzed in the Si layer, occasionally accompanied by complete dissolution of cell-wall portions. This is also in conformity with the previous conclusion that the cellulases hydrolyze highly ordered zones of cellulose and remove hemicelluloses by hydrolysis or by detachment. 

Analyses of the hemicelluloses of woods indicate the presence of a high proportion of D-xylose residues in association with those of a methyl ether of a hexuronic acid.64 The first evidence for the chemical structure of such wood xylans came from the isolation of xylobiose, xylotriose,65 and the aldobiouronic acid 0-(4-0-methyl-a-D-glucosyluronic)-(l —> 2)-D-xylose acid (IX)22 from partial hydrolyzates of aspen wood. The role of such oligosaccharide fragments in wood xylans became more apparent as the result of a study of a xylan from European beechwood,26 in which it was shown... 

Recognizing the need for a more uniform, polysaccharide material for detailed constitutional studies, O Dwyer prepared two hemicellulose fractions from beechwood previously extracted with water and 0.2% sodium hydroxide. As in previous work, the hemicelluloses were extracted from beechwood sawdust with 4% aqueous sodium hydroxide. Pectic materials were precipitated with lime-water, and a fraction designated hemicellu-lose-A was obtained by acidifying the solution with acetic acid. To the filtrate, from hemicellulose-A, was added 95 % ethanol to precipitate hemi-cellulose-B. After further purification, both of these hemicelluloses were subjected to chemical study. Hemicellulose-A ([ccjn —107° in 1 % sodium hydroxide) was observed to be soluble in cold water when freshly prepared, but it was insoluble after being dried. The preparation did not reduce... 

Returning to studies on oak hemicelluloses, O DwyeF obtained hemi-celluloses-A and -B from both heartwood and sapwood of oak, by techniques similar to those applied to beechwood. Not only were hemicellu-loses-A and -B different in physical and chemical properties, but differences... 

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