Advertisement

BioEnergy Research

, Volume 6, Issue 2, pp 405–415 | Cite as

Substrate-Related Factors Affecting Enzymatic Saccharification of Lignocelluloses: Our Recent Understanding

  • Shao-Yuan Leu
  • J. Y. Zhu
Article

Abstract

Enzymatic saccharification of cellulose is a key step in conversion of plant biomass to advanced biofuel and chemicals. Many substrate-related factors affect saccharification. Rather than examining the role of each individual factor on overall saccharification efficiency, this study examined how each factor affects the three basic processes of a heterogeneous biochemistry reaction: (1) substrate accessibility to cellulose—the roles of component removal and size reduction by pretreatments, (2) substrate and cellulase reactivity limited by component inhibition, and (3) reaction conditions—substrate-specific optimization. Our in-depth analysis of published literature work, especially those published in the last 5 years, explained and reconciled some of the conflicting results in literature, especially the relative importance of hemicellulose vs. lignin removal and substrate size reduction on enzymatic saccharification of lignocelluloses. We concluded that hemicellulose removal is more important than lignin removal for creating cellulase accessible pores. Lignin removal is important when alkaline-based pretreatment is used with limited hemicellulose removal. Partial delignification is needed to achieve satisfactory saccharification of lignocelluloses with high lignin content, such as softwood species. Rather than using passive approaches, such as washing and additives, controlling pretreatment or hydrolysis conditions, such as pH, to modify lignin surface properties can be more efficient for reducing or eliminating lignin inhibition to cellulase, leading to improved lignocellulose saccharification.

Keywords

Enzymatic hydrolysis/saccharification Pretreatment Biofuel and biorefinery Lignocelluloses Cellulase enzymes Lignin Accessibility 

Notes

Acknowledgments

We would like acknowledge the financial support from the Agriculture and Food Research Initiative Competitive grant no. 2011-68005-30416, USDA National Institute of Food and Agriculture (NIFA), through the Northwest Advanced Renewables Alliance (NARA), that made the post-doctoral appointment of Leu at the US Forest Service (USFS), Forest Products Laboratory (FPL) possible. We would also like to acknowledge Novozymes North America for their constant support by complementary providing cellulase enzymes, Fred Matt of USFS-FPL for conducting detailed chemical composition analysis, Tom Kuster (USFS-FPL) and Prof. Kecheng Li of University of New Brunswick (Canada) for the SEM and FE-SEM work, and Dr. Scott McNeil and his colleagues at SAIC-Frederick of National Cancer Institute for TEM work. Lastly, but not the least, many past visiting students and scholars at Zhu’s laboratory at FPL are acknowledged for their dedicated work that produced most of the results presented.

References

  1. 1.
    Lynd LR, Laser MS, Bransby D, Dale BE, Davison B, Hamilton R et al (2008) How biotech can transform biofuels. Nat Biotechnol 26:169–172PubMedCrossRefGoogle Scholar
  2. 2.
    Zhu JY, Zhuang XS (2012) Conceptual net energy output for biofuel production from lignocellulosic biomass through biorefining. Prog Energy Combust Sci 38(4):583–589CrossRefGoogle Scholar
  3. 3.
    Mansfield SD, Mooney C, Saddler JN (1999) Substrate and enzyme characteristics that limit cellulose hydrolysis. Biotechnol Prog 15:804–816PubMedCrossRefGoogle Scholar
  4. 4.
    Hall M, Bansal P, Lee JH, Realff MJ, Bommarius AS (2010) Cellulose crystallinity—a key predictor of the enzymatic hydrolysis rate. FEBS J 277(6):1571–1582PubMedCrossRefGoogle Scholar
  5. 5.
    Zhang YHP, Lynd LR (2004) Toward an aggregated understanding of enzymatic hydrolysis of cellulose: noncomplexed cellulase systems. Biotechnol Bioeng 88(7):797–824PubMedCrossRefGoogle Scholar
  6. 6.
    Henrissat B (1994) Cellulases and their interaction with cellulose. Cellulose 1(3):169–196CrossRefGoogle Scholar
  7. 7.
    Teeri TT (1997) Crystalline cellulose degradation: new insight into the function of cellobiohydrolases. Trends Biotechnol 15(5):160–167CrossRefGoogle Scholar
  8. 8.
    Zhao X, Zhang L, Liu D (2012) Biomass recalcitrance. Part I: the chemical compositions and physical structures affecting the enzymatic hydrolysis of lignocellulose. Biofuels, Bioprod Biorefin 6(4):465–482CrossRefGoogle Scholar
  9. 9.
    Himmel ME, Ding SY, Johnson DK, Adney WS, Nimlos MR, Brady JW et al (2007) Biomass recalcitrance: engineering plants and enzymes for biofuels production. Science 315(5813):804–807PubMedCrossRefGoogle Scholar
  10. 10.
    Fan L, Lee YH, Beardmore DH (1980) Mechanism of the enzymatic hydrolysis of cellulose: effects of major structural features of cellulose on enzymatic hydrolysis. Biotechnol Bioeng 22(1):177–199CrossRefGoogle Scholar
  11. 11.
    Stone JE, Scallan AM, Donefer E, Ahlgren E (1969) Digestibility as a simple function of a molecule of similar size to a cellulase enzyme. In: Hajny GJ, Reese ET (eds) Cellulases and their applications., pp 219–241CrossRefGoogle Scholar
  12. 12.
    Zhu J, Wang G, Pan X, Gleisner R (2009) Specific surface to evaluate the efficiencies of milling and pretreatment of wood for enzymatic saccharification. Chem Eng Sci 64(3):474–485CrossRefGoogle Scholar
  13. 13.
    Dasari RK, Berson RE (2007) The effect of particle size on hydrolysis reaction rates and rheological properties in cellulosic slurries. Appl Biochem Biotechnol 137:289–299PubMedCrossRefGoogle Scholar
  14. 14.
    Vidal BC Jr, Dien BS, Ting KC, Singh V Jr (2011) Influence of feedstock particle size on lignocellulose conversion—a review. Appl Biochem Biotechnol 164(8):1405–1421PubMedCrossRefGoogle Scholar
  15. 15.
    Yang B, Wyman CE (2004) Effect of xylan and lignin removal by batch and flowthrough pretreatment on the enzymatic digestibility of corn stover cellulose. Biotechnol Bioeng 86(1):88–95PubMedCrossRefGoogle Scholar
  16. 16.
    Studer MH, DeMartini JD, Davis MF, Sykes RW, Davison B, Keller MT GA et al (2011) Lignin content in natural Populus variants affects sugar release. Proc Natl Acad Sci (PNAS) 108(15):6300–6305CrossRefGoogle Scholar
  17. 17.
    Yu Z, Jameel H, Chang H, Park S (2011) The effect of delignification of forest biomass on enzymatic hydrolysis. Bioresour Technol 102(19):9083–9089PubMedCrossRefGoogle Scholar
  18. 18.
    Zhu W, Houtman CJ, Zhu JY, Gleisner R, Chen KF (2012) Quantitative predictions of bioconversion of aspen by dilute acid and SPORL pretreatments using a unified combined hydrolysis factor (CHF). Process Biochem 47:785–791CrossRefGoogle Scholar
  19. 19.
    Wang ZJ, Zhu JY, Gleisner R, Chen KF (2012) Ethanol production form poplar wood the rough enzymatic saccharification and fermentation by dilute acid and SPORL pretreatments. Fuel 95:606–614CrossRefGoogle Scholar
  20. 20.
    Moxley G, Gaspar AR, Higgins D, Xu H (2012) Structural changes of corn stover lignin during acid pretreatment. J Ind Microbiol Biotechnol 39:1289–1299PubMedCrossRefGoogle Scholar
  21. 21.
    Nakagame S, Chandra RP, Kadla JF, Saddler JN (2011) Enhancing the enzymatic hydrolysis of lignocellulosic biomass by increasing the carboxylic acid content of the associated lignin. Biotechnol Bioeng 108(3):538–548PubMedCrossRefGoogle Scholar
  22. 22.
    Nakagame S, Chandra RP, Saddler JN (2011) The influence of lignin on the enzymatic hydrolysis of pretreated biomass substrates. In: Zhu JY, Zhang X, Pan XJ (eds) Sustainable production of fuels, chemicals, and fibers from forest biomass. American Chemical Society, Washington, DC, pp 145–167CrossRefGoogle Scholar
  23. 23.
    Vidal BC, Dien BS, Ting K, Singh V (2011) Influence of feedstock particle size on lignocellulose conversion—a review. Appl Biochem Biotechnol 164(8):1–17CrossRefGoogle Scholar
  24. 24.
    Zhu W, Zhu JY, Gleisner R, Pan XJ (2010) On energy consumption for size-reduction and yield from subsequent enzymatic saccharification of pretreated lodgepole pine. Bioresour Technol 101(8):2782–2792PubMedCrossRefGoogle Scholar
  25. 25.
    Mooney CA, Mansfield SD, Beatson RP, Saddler JN (1999) The effect of fiber characteristics on hydrolysis and cellulase accessibility to softwood substrates. Enzyme Microb Technol 25(8–9):644–650CrossRefGoogle Scholar
  26. 26.
    Del Rio LF, Chandra RP, Saddler JN (2012) Fibre size does not appear to influence the ease of enzymatic hydrolysis of organosolv-pretreated softwoods. Bioresour Technol 107:235–242PubMedCrossRefGoogle Scholar
  27. 27.
    Arantes V, Saddler JN (2010) Access to cellulose limits the efficiency of enzymatic hydrolysis: the role of amorphogenesis. Biotechnol Biofuels 3(4)Google Scholar
  28. 28.
    Kim TH, Kim JS, Sunwoo C, Lee Y (2003) Pretreatment of corn stover by aqueous ammonia. Bioresour Technol 90(1):39–47PubMedCrossRefGoogle Scholar
  29. 29.
    Chang VS, Holtzapple MT (2000) Fundamental factors affecting biomass enzymatic reactivity. Appl Biochem Biotechnol 84(1):5–37PubMedCrossRefGoogle Scholar
  30. 30.
    Kumar R, Wyman CE (2009) Access of cellulase to cellulose and lignin for poplar solids produced by leading pretreatment technologies. Biotechnol Prog 25(3):807–819PubMedCrossRefGoogle Scholar
  31. 31.
    Mooney CA, Mansfield SD, Touhy MG, Saddler JN (1998) The effect of initial pore volume and lignin content on the enzymatic hydrolysis of softwoods. Bioresour Technol 64(2):113–119CrossRefGoogle Scholar
  32. 32.
    Jeoh T, Ishizawa CI, Davis MF, Himmel ME, Adney WS, Johnson DK (2007) Cellulase digestibility of pretreated biomass is limited by cellulose accessibility. Biotechnol Bioeng 98(1):112–122PubMedCrossRefGoogle Scholar
  33. 33.
    Ishizawa CI, Jeoh T, Adney WS, Himmel ME, Johnson DK, Davis MF (2009) Can delignification decrease cellulose digestibility in acid pretreated corn stover? Cellulose 16(4):677–686CrossRefGoogle Scholar
  34. 34.
    Rollin JA, Zhu Z, Sathitsuksanoh N, Zhang Y-HP (2011) Increasing cellulose accessibility is more important than removing lignin: a comparison of cellulose solvent-based lignocellulose fractionation and soaking in aqueous ammonia. Biotechnol Bioenerineering 108(1):22–30CrossRefGoogle Scholar
  35. 35.
    Zhang J, Wang M, Gao M, Fang X, Yano S, Qin S et al (2012) Efficient acetone–butanol–ethanol production from corncob with a new pretreatment technology—wet disk milling. Bioenergy Res. doi: 10.1007/s12155-012-9226-y
  36. 36.
    Cowling EB, Kirk TK (1976) Properties of cellulose and lignocellulosic materials as substrates for enzymatic conversion processes. Biotech Bioeng Symp 6:95–123Google Scholar
  37. 37.
    Luo XL, Zhu JY, Gleisner R, Zhan HY (2011) Effects of wet-pressing-induced fiber hornification on enzymatic saccharification of lignocelluloses. Cellulose 18(4):1055–1062CrossRefGoogle Scholar
  38. 38.
    Luo X, Zhu JY (2011) Effects of drying-induced fiber hornification on enzymatic saccharification of lignocelluloses. Enzyme Microb Technol 48(1):92–99PubMedCrossRefGoogle Scholar
  39. 39.
    Maloney TC, Stenius P, Paulapuro H (1998) Hydroation and swelling of pulp fibers measured by differential scanning calorimetry. Nordic Pulp Paper Res J 13(1):31–36CrossRefGoogle Scholar
  40. 40.
    Li TQ, Haggkvist M, Odberg L (1997) Porous structure of cellulose fibers studied by Q-space NMR imaging. Langmuir 13:3570–3574CrossRefGoogle Scholar
  41. 41.
    Felby C, Thygesen LG, Kristensen JB, Jørgensen H, Elder T (2008) Cellulose–water interactions during enzymatic hydrolysis as studied by time domain NMR. Cellulose 15(5):703–710CrossRefGoogle Scholar
  42. 42.
    Hui L, Liu Z, Ni Y (2009) Characterization of high-yield pulp (HYP) by the solute exclusion technique. Bioresour Technol 100(24):6630–6634PubMedCrossRefGoogle Scholar
  43. 43.
    Stone JE, Scallan AM (1967) The effect of component removal upon the porous structure of the cell wall of wood. II. Swelling in water and the fiber saturation point. TAPPI J 50(10):496–501Google Scholar
  44. 44.
    Chen Y, Wang Y, Wan J, Ma Y (2010) Crystal and pore structure of wheat straw cellulose fiber during recycling. Cellulose 17:329–338CrossRefGoogle Scholar
  45. 45.
    Brunauer S, Emmet PH, Teller E (1938) Adsorption of gases in multimolecular layers. J Am Chem Soc 60:309–319CrossRefGoogle Scholar
  46. 46.
    Esteghlalian AR, Bilodeau M, Mansfield SD, Saddler JN (2001) Do enzymatic hydrolyzability and Simons' stain reflect the changes in the accessibility of lignocellulosic substrates to cellulase enzymes? Biotechnol Prog 17(6):1049–1054PubMedCrossRefGoogle Scholar
  47. 47.
    Chandra R, Ewanick S, Hsieh C, Saddler JN (2008) The characterization of pretreated lignocellulosic substrates prior to enzymatic hydrolysis, part 1: a modified Simons' staining technique. Biotechnol Prog 24(5):1178–1185PubMedCrossRefGoogle Scholar
  48. 48.
    Hong J, Ye X, Zhang Y-HP (2007) Quantitative determination of cellulose accessibility to cellulase based on adsorption of a nonhydrolytic fusion protein containing CBM and GFP with its applications. Langmuir 23:12535–12540PubMedCrossRefGoogle Scholar
  49. 49.
    Wang QQ, He Z, Zhu Z, Zhang Y-HP, Ni Y, Luo XL et al (2012) Evaluations of cellulose accessibilities of lignocelluloses by solute exclusion and protein adsorption techniques. Biotechnol Bioeng 109(2):381–389PubMedCrossRefGoogle Scholar
  50. 50.
    Zhu Z, Sathitsuksanoh N, Vinzant T, Schell DJ, McMillan JD, Zhang Y-HP (2009) Comparative study of corn stover pretreated by dilute acid and cellulose solvent-based lignocellulose fractionation: enzymatic hydrolysis, supramolecular structure, and substrate accessibility. Biotechnol Bioeng 103(4):715–724PubMedCrossRefGoogle Scholar
  51. 51.
    Liu H, Zhu JY, Chai XS (2011) In situ, rapid, and temporally resolved measurements of cellulase adsorption onto lignocellulosic substrates by UV–vis spectrophotometry. Langmuir 27(1):272–278PubMedCrossRefGoogle Scholar
  52. 52.
    Yang B, Wyman CE (2006) BSA treatment to enhance enzymatic hydrolysis of cellulose in lignin containing substrates. Biotechnol Bioeng 94(4):611–617PubMedCrossRefGoogle Scholar
  53. 53.
    Luo X, Zhu JY, Gleisner R, Zhan HY (2011) Effect of wet pressing-induced fiber hornification on enzymatic saccharification of lignocelluloses. Cellulose 18:1339–1344CrossRefGoogle Scholar
  54. 54.
    Scallan AM (1974) The structure of the cell wall of wood—a consequence of anisotropic inter-microfibrillar bonding? Wood Sci 6:266–271Google Scholar
  55. 55.
    Zhu JY, Pan XJ, Wang GS, Gleisner R (2009) Sulfite pretreatment (SPORL) for robust enzymatic saccharification of spruce and red pine. Bioresour Technol 100(8):2411–2418PubMedCrossRefGoogle Scholar
  56. 56.
    Wong KKY, Deverell KF, Mackie KL, Clark TA, Donaldson LA (1988) The relationship between fiber–porosity and cellulose digestibility in steam–exploded Pinus radiata. Biotechnol Bioeng 31(5):447–456PubMedCrossRefGoogle Scholar
  57. 57.
    Clark T, Mackie K, Dare P, McDonald A (1989) Steam explosion of the softwood Pinus radiata with sulphur dioxide addition. II. Process characterisation. J Wood Chem Technol 9(2):135–166CrossRefGoogle Scholar
  58. 58.
    Thompson DN, Chen HC, Grethlein HE (1992) Comparison of pretreatment methods on the basis of available surface area. Bioresour Technol 39(2):155–163CrossRefGoogle Scholar
  59. 59.
    Grethlein HE (1985) The effect of pore size distribution on the rate of enzymatic hydrolysis of cellulosic substrates. Nat Biotechnol 3(2):155–160CrossRefGoogle Scholar
  60. 60.
    Grous WR, Converse AO, Grethlein HE (1986) Effect of steam explosion pretreatment on pore size and enzymatic hydrolysis of poplar. Enzyme Microb Technol 8(5):274–280CrossRefGoogle Scholar
  61. 61.
    McCann MC, Carpita NC (2008) Designing the deconstruction of plant cell walls. Curr Opin Plant Biol 11(3):314–320PubMedCrossRefGoogle Scholar
  62. 62.
    Ding SY, Himmel ME (2006) The maize primary cell wall microfibril: a new model derived from direct visualization. J Agric Food Chem 54(3):597–606PubMedCrossRefGoogle Scholar
  63. 63.
    Cosgrove DJ (2005) Growth of the plant cell wall. Nat Rev Mol Cell Biol 6(11):850–861PubMedCrossRefGoogle Scholar
  64. 64.
    Park YB, Cosgrove DJ (2012) A revised architecture of primary cell walls based on biomechanical changes induced by substrate-specific endoglucanases. Plant Physiol 158(4):1933–1943PubMedCrossRefGoogle Scholar
  65. 65.
    Carpita NC, McCann MC (2008) Maize and sorghum: genetic resources for bioenergy grasses. Trends Plant Sci 13(8):415–420PubMedCrossRefGoogle Scholar
  66. 66.
    Mosier N, Wyman C, Dale B, Elander R, Lee YY, Holtzapple M et al (2005) Features of promising technologies for pretreatment of lignocellulosic biomass. Bioresour Technol 96(6):673–686PubMedCrossRefGoogle Scholar
  67. 67.
    Wyman CE, Balan V, Dale BE, Elander RT, Falls M, Hames B et al (2011) Comparative data on effects of leading pretreatments and enzyme loadings and formulations on sugar yields from different switchgrass sources. Bioresour Technol 102(24):11052–11062PubMedCrossRefGoogle Scholar
  68. 68.
    Zhu JY, Verrill SP, Liu H, Herian VL, Pan XJ, Rockwood DL (2011) On polydispersity of plant biomass recalcitrance and its effects on pretreatment optimization for sugar production. Bioenergy Res 4(3):201–210CrossRefGoogle Scholar
  69. 69.
    Zhu JY, Zhu W, OBryan P, Dien BS, Tian S, Gleisner R et al (2010) Ethanol production from SPORL-pretreated lodgepole pine: preliminary evaluation of mass balance and process energy efficiency. Appl Microbiol Biotechnol 86(5):1355–1365PubMedCrossRefGoogle Scholar
  70. 70.
    Pan XJ, Xie D, Gilkes N, Gregg DJ, Saddler JN (2005) Strategies to enhance the enzymatic hydrolysis of pretreated softwood with high residual lignin content. Appl Biochem Biotechnol 121:1069–1079PubMedCrossRefGoogle Scholar
  71. 71.
    Lai Y-Z (1990) Chemical degradation. In: Hon DNS, Shiraishi N (eds) Wood and cellulosic chemistry. Marcel Dekker, New York, pp 455–523Google Scholar
  72. 72.
    Clark TA, Mackie KL (1987) Steam explosion of the softwood Pinus radiata with pulphur dioxide addition. I. Process optimization. J Wood Chem Technol 7:373–403CrossRefGoogle Scholar
  73. 73.
    Zhu JY (2011) Physical pretreatment—woody biomass size-reduction—for forest biorefinery. In: Zhu JY, Zhang X, Pan XJ (eds) Sustainable production of fuels, chemicals, and fibers from forest biomass. American Chemical Society, Washington, DC, pp 89–107CrossRefGoogle Scholar
  74. 74.
    Zhu JY, Pan XJ (2010) Woody biomass pretreatment for cellulosic ethanol production: technology and energy consumption evaluation. Bioresour Technol 101:4992–5002PubMedCrossRefGoogle Scholar
  75. 75.
    Hartman RR (1985) Mechanical treatment of pulp fibers for paper property development. In: The 8th Fundamental Research Symposium: Papermaking Raw Materials 1985. Mechanical Engineering Publications Limited, Oxford, England, pp. 413–442Google Scholar
  76. 76.
    Kerekes RJ (2005) Characterizing refining actions: linking the process to refining results. . In: PIRA 2005 Refining Conference. Barcelona, SpainGoogle Scholar
  77. 77.
    Dekker J (2003) New insights in beating leading to innovative beating techniques In: PIRA 2003 Refining Conference. Stockholm, SwedenGoogle Scholar
  78. 78.
    Uetani K, Yano H (2011) Nanofibrillation of wood pulp using a high-speed blender. Biomacromolecules 12(2):348–353PubMedCrossRefGoogle Scholar
  79. 79.
    Iwamoto S, Nakagaito AN, Yano H (2007) Nano-fibrillation of pulp fibers for the processing of transparent nanocomposites. Appl Phys A: Mater Sci Process 89:461–466CrossRefGoogle Scholar
  80. 80.
    Stelte W, Sanadi AR (2009) Preparation and characterization of cellulose nanofibers from two commercial hardwood and softwood pulps. Ind Eng Chem Res 48(24):11211–11219CrossRefGoogle Scholar
  81. 81.
    Wang QQ, Zhu JY, Gleisner R, Kuster TA, Baxa U, McNeil SE (2012) Morphological development of cellulose fibrils of a bleached eucalyptus pulp by mechanical fibrillation. Cellulose 19(5):1631–1643CrossRefGoogle Scholar
  82. 82.
    Monavari S, Gable M, Zacchi G (2009) Impact of impregnation time and chip size on sugar yield in pretreatment of softwood for ethanol production. Bioresour Technol 100:6312–6316PubMedCrossRefGoogle Scholar
  83. 83.
    Zhu JY, Pan XJ, Zalesny RS Jr (2010) Pretreatment of woody biomass for biofuel production: energy efficiency, technologies and recalcitrance. Appl Microbiol Biotechnol 87:847–857PubMedCrossRefGoogle Scholar
  84. 84.
    Agarwal UP, Zhu JY, Ralph SA (2012) Enzymatic hydrolysis of loblolly pine: effects of cellulose crystallinity and delignification. Holtzforchung (in press)Google Scholar
  85. 85.
    Ximenes E, Kim Y, Mosier N, Dien B, Ladisch M (2010) Inhibition of cellulases by phenols. Enzyme Microb Technol 46(3–4):170–176CrossRefGoogle Scholar
  86. 86.
    Sewalt VJH, Glasser WG, Beauchemin KA (1997) Lignin impact on fiber degradation. 3. Reversal of inhibition of enzymatic hydrolysis by chemical modification of lignin and by additives. J Agric Food Chem 45(5):1823–1828CrossRefGoogle Scholar
  87. 87.
    Duarte GC, Moreira LRS, Jaramillo PMD, Filho EXF (2012) Biomass-derived inhibitors of holocellulases. Bioenerg Res 5(3):768–777CrossRefGoogle Scholar
  88. 88.
    Qing Q, Yang B, Wyman CE (2010) Xylooligomers are strong inhibitors of cellulose hydrolysis by enzymes. Bioresour Technol 101(24):9624–9630PubMedCrossRefGoogle Scholar
  89. 89.
    Nagle NJ, Elander RT, Newman MM, Rohrback BT, Ruiz RO, Torget RW (2002) Efficacy of a hot washing process for pretreated yellow poplar to enhance bioethanol production. Biotechnolo Prog 18:734–738CrossRefGoogle Scholar
  90. 90.
    Liu H, Zhu JY (2010) Eliminating inhibition of enzymatic hydrolysis by lignosulfonate in unwashed sulfite-pretreated aspen using metal salts. Bioresour Technol 101(23):9120–9127PubMedCrossRefGoogle Scholar
  91. 91.
    Eriksson T, Borjesson J, Tjerneld F (2002) Mechanism of surfactant effect in enzymatic hydrolysis of lignocellulose. Enzyme Microb Technol 31(3):353–364CrossRefGoogle Scholar
  92. 92.
    Borjesson J, Peterson R, Tjerneld F (2007) Enhanced enzymatic conversion of softwood lignocellulose by poly(ethylene glycol) addition. Enzyme Microb Technol 40(4):754–762CrossRefGoogle Scholar
  93. 93.
    Tu MB, Zhang X, Paice M, McFarlane P, Saddler JN (2009) Effect of surfactants on separate hydrolysis fermentation and simultaneous saccharification fermentation of pretreated lodgepole pine. Biotechnol Prog 25:1122–1129PubMedCrossRefGoogle Scholar
  94. 94.
    Ooshima H, Burns DS, Converse AO (1990) Adsorption of cellulase from Trichoderma reesei on cellulose and lignacious residue in wood pretreated by dilute sulfuric acid with explosive decompression. Biotechnol Bioeng 36:446–452PubMedCrossRefGoogle Scholar
  95. 95.
    Zheng Y, Pan Z, Zhang R, Wang D, Jenkins B (2008) Non-ionic surfactants and non-catalytic protein treatment on enzymatic hydrolysis of pretreated creeping wild ryegrass. Appl Biochem Biotechnol 146:231–248PubMedCrossRefGoogle Scholar
  96. 96.
    Liu H, Zhu JY, Fu S (2010) Effects of lignin-metal complexation on enzymatic hydrolysis of cellulose. J Agric Food Chem 58:7233–7238PubMedCrossRefGoogle Scholar
  97. 97.
    Pan XJ, Zhang X, Gregg DJ, Saddler JN (2004) Enhanced enzymatic hydrolysis of steam-exploded Douglas fir wood by alkali-oxygen post-treatment. Appl Biochem Biotechnol 113–16:1103–1114CrossRefGoogle Scholar
  98. 98.
    Nakagame S, Chandra RP, Saddler JN (2010) The effect of isolated lignins, obtained from a range of pretreated lignocellulosic substrates, on enzymatic hydrolysis. Biotechnol Bioeng 105(5):871–879PubMedGoogle Scholar
  99. 99.
    Kumar L, Chandra R, Saddler JN (2011) Influence of steam pretreatment severity on post-treatments used to enhance the enzymatic hydrolysis of pretreated softwoods at low enzyme loadings. Biotechnol Bioeng 108(10):2300–2311CrossRefGoogle Scholar
  100. 100.
    Li J, Henriksson G, Gellerstedt G (2007) Lignin depolymerization/repolymerization and its critical role for delignification of aspen wood by steam explosion. Bioresour Technol 98(16):3061–3068PubMedCrossRefGoogle Scholar
  101. 101.
    Wang ZJ, Lan TQ, Zhu JY (2012) Lignosulfonate and elevated pH can enhance enzymatic hydrolysis of lignocelluloses. Biotechnol Biofuels 5Google Scholar
  102. 102.
    Lan TQ, LOU H, Zhu JY (2012) Enzymatic saccharification of lignocelluloses should be conducted at elevated pH 5.5 to 6.2. Bioenerg Res. doi: 10.1007/s12155-012-9273-4

Copyright information

© Springer Science+Business Media New York (outside the USA) 2012

Authors and Affiliations

  1. 1.USDA Forest Service, Forest Products LaboratoryMadisonUSA
  2. 2.Dept. of Biological Systems EngineeringUniversity of Wisconsin-MadisonMadisonUSA

Personalised recommendations