Enzymes hemicellulose treatment

Endoxylanase produced by a transformant strain of Escherichia coli has been shown to decrease the kappa number and increase the brightness of pulp in an enzymatic pretreatment followed by chemical extraction (27). Beta-xylosidase, on the other hand, had no effect in the treatment. The mannanase produced by Bacillus suhtilis was found to be equally effective as the xylanase. The specificities of mannanases produced by two different organisms, however, differed considerably 49). Enrichment of the culture broth of Streptomyces olivochromogenes, containing mainly endoxylanase, with different pure enzymes or enzyme mixtures acting on side chains and other hemicelluloses, resulted only in slight increases in brightness and in kappa number reduction (55). 

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. 

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-... 

Hemicellulose-B(Table V) from sapwood gave a blue color with iodine, which disappeared after treatment with Takadiastase under carefully controlled conditions. The solution was found to contain n-glucose, and its reducing value was equivalent to 24.6% of hexosan. On the basis of analytical data, heartwood hemicellulose-B appeared to be similar in constitution to the polysaccharide (6 anhydro-n-xylose units and 1 0-methyl-hexuronic acid per structural unit) isolated- after prolonged enzymic hydrolysis of heartwood hemicellulose-A. 

Attempts have been made to estimate the proportion of B-fraction by removal of the A-fraction through hydrolysis with various enzymes. Since it is now recognized that the B-fraction undergoes partial conversion, these estimates are of little value. Treatment of gelatinized cereal starches with certain amylases gives a flocculent precipitate, variously termed hemicellulose or amylocellulose. This appears to be a degraded A-fraction, rendered insoluble through adsorption of fatty acids present in the substratum and also by deterioration of the protective colloid action afforded by the B-fraction. 

For the enzymatic process, the feedstock is first pretreated with a dilute acid to break down the lignocellu-lose into lignin, hemicellulose, and cellulose. Enzymes called cellulases and xylanases are then used to break down the cellulose and hemicellulose fractions into six- and five- carbon sugars, respectively. Without the dilute acid treatment, the enzymes would not be able to come in efficient contact with the cellulose and hemicellulose. The sugars are then fermented to ethanol using organisms such as E. S. cerevisiaeP ... 

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