Selective Biosynthesis Of Xylanases And The Application Of Cellulase-poor Xylanases

This article focuses on those three topics: the biosynthesis and purification of xylanases by Trichoderma reesei;the selective biodegradation of xylan extractives and the reused of unhydrolyzed xylan; xylanase pretreatment of Wujiang wheat straw pulp.Major experimental results are as follow:1 Three periods of time between two and five hours were separated from the culture filtrate: slowly increased and much at high speed and steadily.Filamentous fungi are particularly interesting producers of xylanases from an industrial point of view,due to the fact that they excrete xylan-degrading enzymes into the medium,thus eliminating the need for cell discruption.Furthermore,xylanase levels from fungal cultures are generally much higher than those from yeast or bacteria. The choice of an appropriate substrate is of great importance for the successful production of xylanases.2 Effect of inducing substrate.The substrate not only serves as carbon and energy source.but also provides the necessary prolonged production phase can result in an increased overall productivity of the fermentation process. As can be concluded from the inducibility of xylanases by low-molecular-mass compounds directly derived from xylan, purified xylans can be excellent substrates and are frequently used for small-scale experiments.With a number of different organisms these rather pure.defmed substrates not only results in increased yields of xylanase.but often caused a selective induction of xylanase with no or only low concomitantly formed cellulase activities. When cultivated on xylan mixed with Wujiang wheat straw pulp.cellulase production significantly increased at higher temperature whereas xylanase formation was reduced. The biosynthesis of xylanases could be greatly induced by xylan mixed with soybean power or coase fibre as carbon source, and which could improve the xylanase activity.Compared to the xylan(13 g/1), xylan (10 g/1) mixed with soybean power or coase fibre as carbon source, extracellular protein density were 0.368mg/ml and 0.412mg/ml,lower than substituded-xylan extractives which is the solid residue after enzymatic hydrolysis of corncob xylan and is determined to contain much low molecular weight component, secondly.cellulosase activity were 0.167IU/ml and 0.159IU/ml, lower too, thirdly, FPase were 0.81FPIU/g and 0.85FPIU/g, higher than it, respectively.The latter are better than the former. For larger-scale production processes since the cost of the substrate plays a crucial role in the economics of an enzyme production, different lignocellulosic substrates were prepared and assessed in relation to pure substrates such as xylan or cellulose, in several different studies.As show in Table 7,the c source were employed in concentration up to 13g/l.An increase in the substrate concentration proved to be beneficial for Trichoderma reesei, where raising the substrate(the enzymatic hydrolysis residue)from 7g/l to 10g/1 resulted in an almost twofold extra of xylanase ratio activity 108.75IU/mgpro.An increase in the concentration of the inducing substrate xylan from lOg/1 to 13g/l was, however, found to have negetive consequences for the formation of xylanase.At 7g/l,10g/l,13g/l xylan extractive substrate concentration, 10g/l is the best that xylasase activity 58.3IU/ml, and the xylanase ratio activityto protein density(158IU/mgpro) . Xylanases can be used for more specific hydrolytic purposes,such as the production of oligosaccharides from isolated xylans.(Pellerin et al.,1991; Sasaki et al.,1993). The oligosaccharides thus produced (mainly xylobiose and xylotriose)are used as functional food additives or alternative sweeteners with certain beneficial properties. 10g/I to xylan extractive substrate concentration.the ratio of Xylo-oligosaccharide is the greatest 47.8%.While the concentration increased to 13g/l, enzymatic hydrolysis yield is up to 98%.The reason is that too much substrate bring about concomitance between enzyme and low-melocular pieces .3 The stable pH and the optimal temperature of enzymes were 5.0 and...