Strategies to enhance the enzymatic hydrolysis of pretreated softwood with high residual lignin content

  • Xuejun Pan
  • Dan Xie
  • Neil Gilkes
  • David J. Gregg
  • Jack N. Saddler
Article

Abstract

Pretreatment of Douglas-fir by steam explosion produces a substrate containing approx 43% lignin. Two strategies were investigated for reducing the effect of this residual lignin on enzymatic hydrolysis of cellulose: mild alkali extraction and protein addition. Extraction with cold 1% NaOH reduced the lignin content by only approx 7%, but cellulose to glucose conversion was enhanced by about 30%. Before alkali extraction, addition of exogenous protein resulted in a significant improvement in cellulose hydrolysis, but this protein effect was substantially diminished after alkali treatment. Lignin appears to reduce cellulose hydrolysis by two distinct mechanisms: by forming a physical barrier that prevents enzyme access and by non-productively binding cellulolytic enzymes. Cold alkali appears to selectively remove a fraction of lignin from steam-exploded Douglas-fir with high affinity for protein. Corresponding data for mixed softwood pretreated by organosolv extraction indicates that the relative importance of the two mechanisms by which residual lignin affects hydrolysis is different according to the pre- and post-treatment method used.

Index Entries

Softwood bioconversion pretreatment steam explosion lignin cellulose hydrolysis 

References

  1. 1.
    Galbe, M. and Zacchi, G. (2002), Appl. Microbiol. Biotechnol. 59, 618–628.PubMedCrossRefGoogle Scholar
  2. 2.
    Wu, M. M., Chang, K., Gregg, D. J., Boussaid, A., Beatson, R. P., and Saddler, J. N. (1999), Appl. Biochem. Biotechnol. 77–79, 47–54.CrossRefGoogle Scholar
  3. 3.
    BW McCloy & Associates, I. (2003), Estimated production, consumption and surplus mill residues in British Columbia, a 2003 update. Prepared for Natural Resources Canada.Google Scholar
  4. 4.
    Clark, T. A. and Mackie, K. L. (1987), J. Wood Chem. Technol. 7, 373–403.Google Scholar
  5. 5.
    Ramos, L. P., Breuil, C., and Saddler, J. N. (1992), Appl. Biochem. Biotechnol. 34–35, 37–48.Google Scholar
  6. 6.
    Tengborg, C., Stenberg, K., Galbe, M., et al. (1998), Appl. Biochem. Biotechnol. 70–72, 3–15.Google Scholar
  7. 7.
    Boussaid, A., Esteghlalian, A. R., Gregg, D. J., Lee, K. H. and Saddler, J. N. (2000), Appl. Biochem. Biotechnol. 84–86, 693–705.PubMedCrossRefGoogle Scholar
  8. 8.
    Yang, B., Boussaid, A., Mansfield, S. D., Gregg, D. J., and Saddler, J. N. (2002), Biotechnol. Bioeng. 77, 678–684.PubMedCrossRefGoogle Scholar
  9. 9.
    Pan, X. J., Zhang, X., Gregg, D. J., and Saddler, J. N. (2004), Appl. Biochem. Biotechnol. 113–116, 1103–1114.PubMedCrossRefGoogle Scholar
  10. 10.
    Pan, X. J., Arato, C., Gilkes, N. R., et al. (2004), Biotechnol. Bioeng. in press.Google Scholar
  11. 11.
    Ghose, T. K. (1987), Pure Appl. Chem. 59, 257–268.Google Scholar
  12. 12.
    Wood, T. M. and Bhat, M. (1988), in Methods in Enzymology, Vol. 160, Biomass (Part A, Cellulose and Hemicellulose) (Colowick, S.P. and Kaplan, N.O., eds.). Academic Press, Inc., New York, pp. 87–112.CrossRefGoogle Scholar
  13. 13.
    Dence, C. W. (1992), in Methods in Lignin Chemistry, Lin, S. Y. and Dence, C. W., eds., Springer-Verlag, Berlin, pp. 33–61.Google Scholar
  14. 14.
    Lai, Y.-Z. (1992), In: Methods in Lignin Chemistry, Lin, S. Y. and Dence, C. W., eds., Springer-Verlag, Berlin, pp. 423–434.Google Scholar
  15. 15.
    Montane, D., Farriol, X., Salvado, J., Jollez, P., and Chornet, E. (1998), J. Wood Chem. Technol. 18, 171–191.CrossRefGoogle Scholar
  16. 16.
    Montane, D., Salvado, J., and Farriol, X. (1997), Holzforschung 51, 135–141.CrossRefGoogle Scholar
  17. 17.
    Zimbardi, F., Viggiano, D., Nanna, F., Demichele, M., Cuna, D., and Cardinale, G. (1999), Appl. Biochem. Biotechnol. 77–79, 117–125.CrossRefGoogle Scholar
  18. 18.
    Shevchenko, S. M., Beatson, R. P., and Saddler, J. N. (1999), Appl. Biochem. Biotechnol. 77–79, 867–876.PubMedCrossRefGoogle Scholar
  19. 19.
    Sewalt, V. J. H., Glasser, W. G., and Beauchemin, K. A. (1997), J. Agricul. Food Chem. 45, 1823–1828.CrossRefGoogle Scholar

Copyright information

© Humana Press Inc. 2005

Authors and Affiliations

  • Xuejun Pan
    • 1
  • Dan Xie
    • 1
  • Neil Gilkes
    • 1
  • David J. Gregg
    • 1
  • Jack N. Saddler
    • 1
  1. 1.Forest Products Biotechnology, Faculty of ForestryUniversity of British ColumbiaVancouverCanada

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