Xylanasic enzymatic activity

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-... 

Unlike starch or cellulose, BSG hemicellulose has a complex structure, which is still present, in part, on its autohydrolysis products. Oligosaccharides from BSG hydrolysis consist mainly of branched arabino-xylo-glucurono oligosaccharides that are not highly acetylated when compared to other xylans, such as from Eucalyptus wood (31). The action of several enzymatic activities including endo-l,4-P-xylanase P-xylosidase and accessory activities such as acetyl xylanesterase, a-glucuronidase, and a-arabino-furanosidase is therefore required for the complete hydrolysis of OCL to monosaccharides. 

Table 1 shows the main activities present in the various reaction mixtures using Celluclast 1.5L, Novozym 342, Viscozyme L, Pentopan 500BG, Pulpzyme HC, Multifect Xylanase, and Multifect GC. Although most endoxylanases present in the commercial preparations exhibit optimal activity near 50°C, hydrolysis assays were carried out at a lower temperature (35°C) to increase enzyme stability and to reduce the possibility of inactivation of other enzymatic activities having unknown stability profiles. 

In the enzymatic production of XOS, low enzymatic activities are preferable in order to avoid degradation down to monosaccharides, di-, tri- and tetrasaccharides being the required products [305]. The enzyme used for XOS production is an endo-l-4-/3-xylanase (l,4-/3-D-xylan... 

Fig. 2 Xylanase production in the multi-layer-packed bed reactor with passive aeration conditions a specific activity, b total activity. X represents 50 g of soya oil cake supplemented with 200 ml of the nutritive solution [casein peptone at 0.75% (w/v) and Na2HP04.2H20 at 1% (w/v) in distilled water]. Inoculum is 5.10 spores/gram of soya oil cake or the results of the development of these spores in 1 day (mycelia). The ratio values are averages based on addition of the enzymatic activity from the four layers, and the experiment was performed in triplicate. The deviation standard was below 8% in all cases. Conidial inoculum ...

The composition of multienzyme preparation PC-PEB-9 and enzyme preparation PC-HOST based on P. canescens PCXlnR host strain was determined using Fast Protein Liquid Chromatography (FPLQ and data of enzymatic activities of BGL, PEL, xylanase, and EG2 toward PNPG, citrus pectin, birch wood xylan, and CMC, respectively (Table 3). Enzyme preparatirMi PC-HOST contained 30 % of xylanases. Enzyme preparation PC-PEB-9 consisted of 15 % xylanase, 11 % PEL, 18 % EG2, and 12 % BGL (Bushina et al. 2012). 

Selective inactivation of cellulase activities is another method which has been applied to fungal culture filtrates to produce cellulase-free xylanase preparations. Cellulase inactivation of a crude enzymatic complex was achieved by Barnoud et al. (15) using a 1 mM mercuric chloride solution. In the presence of this sulfhydryl binding metal, complete inactivation of endocellulases was observed whereas the xylanases retained 80% of their activity. 

Although most cellulase enzyme complexes, including Celluclast, contain xylanase activity (data not shown), the amount of released xylose after enzymatic hydrolysis was negligible, especially compared with the amount of released xylose after pretreatment. 

Three enzymatic mixtures with predominantly cellulase and xylanase activity were used for the saccharification tests. To hydrolyse the cellulose, the mixtures Celluclast 1.5L and Novozym 188 from Novo Nordisk were... 

Furthermore, enzymatic hydrolysis of the corn stover treated under optimal AFEX conditions showed almost 98% glucan conversion and 80% xylan conversion vs 29 and 16% for untreated com stover, respectively (at an enzyme loading of 60 FPU/g of glucan). Unlike acidic pretreatments, AFEX does not generate sugar monomers. The cellulase mixture in our study was developed for hydrolysis of acid-pretreated materials and has about 1% by weight xylanase activity (J. Cherry, personal communication, Nov. 2002). Enzyme cocktails with enhanced xylanase activity would presumably completely hydrolyze AFEX-treated xylans. 

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