Xylan hydrolysis

Metal requirements (for activity or stability Main end products from xylan hydrolysis... 

The specificity of a xylanase preparation may be determined from the isolation and characterization of oligosaccharides formed from xylan hydrolysis. While the oligosaccharides released were mainly dependent on the specificity of the xylanase, the complex structure of the heteroxylan also determines the extent of hydrolysis and the site of cleavage. Two types of xylooligosaccharides are usually produced acidic (from glucuronoxylans) and neutral (from arabino- and arabinoglucurono-xylans). The specificity of the action of several purified xylanases on various heteroxylans is shown below ... 

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 overall release of water soluble organic carbon from soil, on which this model for xylan hydrolysis is based, was expressed as three additive terms (15) ... 

This preliminary study suggests that mass transfer models could describe many features of xylan hydrolysis with accuracy similar to that of conventional first-order reaction-only models that have been long used to describe such systems. For example, a simple leaching model can describe release of xylan into solution as the product of a concentration gradient times a mass transfer coefficient. This model predicts that flowthrough operation could improve xylan release compared to a batch system by reducing the concentration in solution and thereby increasing the concen-... 

The main factors affecting monosaccharide recovery in dilute-acid hydrolysis are catalyst concentration, reaction time, and temperature, whereas enzymatic hydrolysis is also dependent on additional factors such as substrate structure, and type and ratio of enzymatic activities present in the commercial enzyme preparations. The most important enzymes for xylan hydrolysis are endo-l,4-(3-xylanases (which attack the main chain) (3-xylosidases (which hydrolyze xylooligosaccharides to xylose) and accessory enzymes, such as acetyl xylanesterases, a-glucu-... 

Figure 3, Effect of solids concentration on xylan hydrolysis yields after 15 minutes at 200°C,...

Figure 5a reveals that this depolymerization model shows trends consistent with data but is not particularly accurate. However, a modified model was developed in which die right-hand side of Equation [5] was multiplied by a first-order reactivity term, a = with a being the reactivity, ka a proportionality constant, and t the time, and application of this model did a much better job of describing the time course of xylan hydrolysis, as shown in Figure 5b. The fact that declining bond reactivity describes the data well suggests that the original assumption that all xylan bonds are broken equally at random is not valid. An obvious next step is the determination of individual bond energies within the hemicellulose molecule and incorporation of this information into a modified model.

McClendon SD, Mao Z, Shin HD, Wagschal K, Chen RR. (2012). Designer xylanosomes protein nanostructures for enhanced xylan hydrolysis. Appl Biochem Biotechnol, 167,395-411. 

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