Xylan degradation rate

The xylan degradation rates relative to those of mannan ranged from 0.3 to 0.4 at the end of the experiment (80 hr). The same values were obtained before the additional action of mannanase on the samples treated with one of the three cellulases for 48 hr (Table III, Column 14). The corresponding values relative to the cellulose degradation rates ranged from 0.5 to 0.7 for the samples treated with cellulase only (48 hr) and after combined cellulase-mannase action (Table III, Column 15). 

The xylanase hydrolyzed about half the xylan in the sprucewood holocellulose. This is in the range of the xylan degradation obtained in former studies with delignified beechwood (7,10,22). Boutelje et al. (5) reported only 20-30% xylan hydrolysis of sprucewood holocellulose by a xylanase, even after repeated treatments. They used the same holocellulose and a xylanase isolated from the same commercial enzyme preparation as were used in the mannanase treatment referred to above. The holocellulose contained only a low xylan portion and very little arabinose this could be the reason for the inferior degradation rate, and hence it is not surprising that no free arabinose was detected, in contrast to what... 

The end group which is produced contains a carboxylic acid functionality which has an influence on the anionicity of pulp fibres (Chapter 6) but, in this form, it is resistant to further alkaline degradation. The hemicelluloses are also able to undergo the same type of peeling reaction but at different rates from each other and from cellulose. The /3-1,4-xylans, for example, are more stable to alkaline degradation than the glucomannans. 

Consistent with the behavior of simple glycosides (Table 2), the homogeneous hydrolysis rate of B-(l-4)-linked polysaccharides, as BeMiller summarized [255, 256], increased in the order cellulose (1) < mannan (2-2.5) < xylan (60-80) < galactan (300). This further demonstrates the significant role of accessibility in acidic degradation reactions. 

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