High Temperature-acid Degradation And Enzymatic Hydrolysis Of Xylan

Plant fiber has the most plentiful stock as a kind of regenerated resource in the earth. And for a long time it hasn't been efficiently utilized. Using xylan extracted" from plant as substrate, this thesis discussed the main effect in preparing xylanases, the selective biosynthesis of cellulose-poor xylanase by regulation. On the other hand, in order to raise utility rate of xylan in functional xylo-oligosaccharide production, this thesis also studied the treatment of enzymatically hydrolized residues by high temperature and acid and the re-enzymatic hydrolysis of its products. The main results are as follows:The category and concentration of carbon source could influence the activity or productivity of xylanases. Coarse xylan or enzymatically hydrolyzed residues could substitute pure xylan for synthesis of high-active xylanases. With them as substrate, the activity of xylanases respectively reached 81.25 IU/ml and 53.16 IU/ml. When the concentration of coarse xylan was 10g/L, xylanase activity reached 151.84 lU/ml and the yield of xylanases reached the top (15184IU/g xylan) . Moreover, mixed nitrogen source was generally better than single nitrogen source in preparation.of xylanases. Mixing ammonium sulfate with carbamide and peptone in specific proportion, the xylanase activity attained 173.52 lU/ml. In addition, High C/N 7-8 could restrain from cellulases and promote xylanses.With coarse xylan as carbon source, mixture of ammonium sulfate, carbamide and peptone as nitrogen source, retaining C/N 7, high-activity xylanases with low CMCase activity could be obtained under integrated regulatory cultivation (the highest ratio of xylanase to CMCase 1314). The Concrete methods of regulation were as follows: the temperature was controlled 35~36 C with initial pH of 6.0 at earlier stage, while at the later stage the temperature was reduced to 25 ~ 26 C.When enzymatically hydrolyzed residues were treated by high temperature, adding to acetic acid could promote xylan to degrade and raise yield of xylo-oligosaccharides. The optimum treatment conditions of enzymatic hydrolysis residues as follows: Adding to 0.3 % ~ 0.5% acetic acid, the temperature was 170C and treatment time was 30 minute. Under such conditions, With raw materials of xylan concentration, 67.4g/L, besides the average polymeric degree of xylan fall to1 .82 ~ 1. 60, the yield of xylo-oligosaccharides reached 36.2 % ~ 38.1% and the loss of xylan was 9.9% ~ 9.1%. While no acid was added, the productivity was only 26.6% and loss of xylan was 10.6%. The HPLC illustration showed that with the mass of filtrate xylan degrading, the yield of total sugar was about 40%and the yield of every kind of oligosaccharide was about 8% which was similar to that of xylose.Through rehydrolysis of filtrate xylan after high temperature and acid degradation, the average polymeric degree of xylan fall to about 1.3. As can be showed in HPLC illustration, with polysaccharide further degrading, the content of xylo-oligosaccharides of average polymeric degree 2-6 reduced from 30.5%-37.5% to 2 6 . 6 % ~ 29. 9 %, also the category of xylo-oligosaccharides decreased to almost xylobiose and xylotriose, but the xylose content prominently increased from 8.2 % ~ 9 . 6 % to 28.2%-36.1%.High temperature and acid degradation of enzymatically hydrolyzed residues not only could make xylan to degrade, which avail to raise yield of xylo-oligosaccharides, but also could make the space stucture of xylan to change, which easy to hydrolyze by enzymes. All that gave evidence for raising yield of xylo-oligosaccharides and cutting down production costs.