Production, characterization and application of thermostable xylanase from Bacillus licheniformis GRE7 | |
| Author | Kiddinamoorthy, Jeyagowri |
| Call Number | AIT Thesis no.FB-04-03 |
| Subject(s) | Bacillus (Bacteria) Xylanases |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis ; no. FB-04-03 |
| Abstract | Bio bleaching of Kraft-pulp by using xylanase is an alternative method to reduce the use of toxic chemicals in paper and pulp technology. The enzyme used this purpose should be active at higher temperature, thermostable, alkaliphilic and cellulase enzyme free. In order to get such an enzyme, known thermophilic bacteria Bacillus licheniformis GRE7 and Bacillus stearothermophilus GREl were compared to select the better xylanase producer without cellulolytic activity. Both thermophiles showed very low cellulolytic activity, the B.licheniformis GRE7 was selected for further study as higher xylanase activity was however, obtained in shorter period with this organism. Xylanse production on 1 % xylan level both in shake flask and 1 litre bioreactor showed 3 fold higher activities than 0.5% xylan level in the bioreactor. The highest activity of xylanase, the increase in cell mass content in culture media and the decrease in oxygen saturation level in the fermentation period indicated that, fermentation up to 20-24 h is enough for the production of xylanase. In case of solid state fermentation using wheat bran, B.licheniformis GRE7 produced 20 fold higher activity of xylanase (4588 U/g bran ) when compared with to that submerged culture in bioreactor and shake flasks. The molecular mass of xylanase was estimated as 25kDa. The enzyme was purified by 3.5 fold with a yield (recovery) of 35%. The optimum temperature and pH for activity was 70°C and 7.Xylanase was stable at 70°C with more than 50% activity after 135 minutes at the neutral pH. The presence of metal ions Mn2+ and Co2+ in reaction mixture increase the activity of the enzyme by two fold as compare the control. The V max and Km of the enzyme of the enzyme is 9.71 mg xylan/sec and 4.38 mg/mL respectively. The relatively low Km value of the enzyme indicates the higher affinity of the enzyme towards the substrate. In the enzymatic treatment of eucalyptus pulp, the chromophore release at 280nm and 465nm, reducing sugar formation, decrease of kappa number % were higher than control level. There was increase in all desirable properties with the increases in enzyme dosages. Eucalyptus bleached pulp pretreated with enzyme gained over 2.5 brightness points over control at 30% of the original level chlorine dioxide level and lead to the reduction of 4.5 kg chlorine dioxide per tone of pulp. The alkalitolerant property, thermostability, absence of cellulolytic activity, the improved brightness and its capacity to reduce chlorine dioxide to 30% level demonstrates the high potential of the enzyme application in bio bleaching of Kraft pulp. |
| Year | 2004 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. FB-04-03 |
| Type | Thesis |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Food Engineering and Bioprocess Technology (FB) |
| Chairperson(s) | Rakshit, Sudip K. |
| Examination Committee(s) | Jindal, Vinod K.; Athapol Noomhorm |
| Scholarship Donor(s) | The Royal Netherland Government |
| Degree | Thesis (M.Sc.) - Asian Institute of Technology, 2004 |