title: Rate-constraining changes in surface properties, porosity and hydrolysis kinetics of lignocellulose in the course of enzymatic saccharification.
abstract: BACKGROUND
  Explaining the reduction of hydrolysis rate during lignocellulose hydrolysis is a challenge for the understanding and modelling of the process. This article reports the changes of cellulose and lignin surface areas, porosity and the residual cellulase activity during the hydrolysis of autohydrolysed wheat straw and delignified wheat straw. The potential rate-constraining mechanisms are assessed with a simplified kinetic model and compared to the observed effects, residual cellulase activity and product inhibition.
  
  
  RESULTS
  The reaction rate depended exclusively on the degree of hydrolysis, while enzyme denaturation or time-dependent changes in substrate hydrolysability were absent. Cellulose surface area decreased linearly with hydrolysis, in correlation with total cellulose content. Lignin surface area was initially decreased by the dissolution of phenolics and then remained unchanged. The dissolved phenolics did not contribute to product inhibition. The porosity of delignified straw was decreased during hydrolysis, but no difference in porosity was detected during the hydrolysis of autohydrolysed straw.
  
  
  CONCLUSIONS
  Although a hydrolysis-dependent increase of non-productive binding capacity of lignin was not apparent, the dependence of hydrolysis maxima on the enzyme dosage was best explained by partial irreversible product inhibition. Cellulose surface area correlated with the total cellulose content, which is thus an appropriate approximation of the substrate concentration for kinetic modelling. Kinetic models of cellulose hydrolysis should be simplified enough to include reversible and irreversible product inhibition and reduction of hydrolysability, as well as their possible non-linear relations to hydrolysis degree, without overparameterization of particular factors.
authors.affiliation: Aalto University, School of Chemical Technology, P.O. Box 16100, FI-00076 Espoo, Finland.
authors.forename: Ville
authors.identifier: 0000-0002-8220-6656
authors.initials: V
authors.lastname: Pihlajaniemi
authors.affiliation: Aalto University, School of Chemical Technology, P.O. Box 16100, FI-00076 Espoo, Finland.
authors.forename: Mika Henrikki
authors.initials: MH
authors.lastname: Sipponen
authors.affiliation: Aalto University, School of Chemical Technology, P.O. Box 16100, FI-00076 Espoo, Finland.
authors.forename: Anne
authors.initials: A
authors.lastname: Kallioinen
authors.affiliation: Aalto University, School of Chemical Technology, P.O. Box 16100, FI-00076 Espoo, Finland.
authors.forename: Antti
authors.initials: A
authors.lastname: Nyyssölä
authors.affiliation: Aalto University, School of Chemical Technology, P.O. Box 16100, FI-00076 Espoo, Finland.
authors.forename: Simo
authors.initials: S
authors.lastname: Laakso
keywords: Cellulases; Cellulose surface; Enzymatic lignocellulose hydrolysis; Inhibition; Kinetic modelling; Lignin surface; Pore size distribution
references.citation: J Biotechnol. 2006 Sep 1;125(2):198-209
references.pmid: 16621087
references.citation: Bioresour Technol. 2014 Oct;169:80-7
references.pmid: 25033327
references.citation: Biotechnol Bioeng. 1984 Mar;26(3):221-30
references.pmid: 18551730
references.citation: Bioresour Technol. 2014 Feb;153:15-22
references.pmid: 24333697
references.citation: Biotechnol Bioeng. 2013 Jan;110(1):127-36
references.pmid: 22811319
references.citation: Enzyme Microb Technol. 2011 Jan 5;48(1):54-60
references.pmid: 22112771
references.citation: J Biol Chem. 2011 Apr 1;286(13):11195-201
references.pmid: 21282110
references.citation: Science. 2011 Sep 2;333(6047):1279-82
references.pmid: 21885779
references.citation: Proc Natl Acad Sci U S A. 1996 Oct 29;93(22):12251-5
references.pmid: 8901566
references.citation: Biotechnol Biofuels. 2015 Apr 01;8:56
references.pmid: 25870653
references.citation: Bioresour Technol. 2012 Dec;126:208-15
references.pmid: 23073110
references.citation: Bioresour Technol. 2012 Oct;121:154-60
references.pmid: 22858480
references.citation: Bioresour Technol. 2010 Dec;101(24):9624-30
references.pmid: 20708404
references.citation: Bioresour Technol. 2012 Apr;110:405-11
references.pmid: 22357287
references.citation: Metab Eng. 2008 Nov;10(6):370-81
references.pmid: 18647658
references.citation: Biotechnol Adv. 2010 May-Jun;28(3):407-25
references.pmid: 20172020
references.citation: Bioresour Technol. 2012 Apr;110:526-33
references.pmid: 22357293
references.citation: J Phys Chem B. 2012 May 31;116(21):6128-36
references.pmid: 22577872
references.citation: Langmuir. 2012 Jun 26;28(25):9664-72
references.pmid: 22646051
references.citation: Enzyme Microb Technol. 2011 Apr 7;48(4-5):408-15
references.pmid: 22112958
references.citation: Biotechnol Biofuels. 2013 Jan 28;6(1):16
references.pmid: 23356676
references.citation: J Biotechnol. 2004 Jan 8;107(1):65-72
references.pmid: 14687972
references.citation: Biotechnol Adv. 2010 May-Jun;28(3):308-24
references.pmid: 20080173
references.citation: Biotechnol Prog. 2004 May-Jun;20(3):698-705
references.pmid: 15176871
references.citation: Biotechnol Lett. 2012 Aug;34(8):1475-82
references.pmid: 22476551
references.citation: Bioresour Technol. 2010 Jul;101(13):4930-5
references.pmid: 19857959
references.citation: Biotechnol Bioeng. 2012 Aug;109(8):1965-75
references.pmid: 22383340
references.citation: Biotechnol Adv. 2009 Nov-Dec;27(6):833-48
references.pmid: 19577626
references.citation: Biotechnol Prog. 2007 Mar-Apr;23(2):398-406
references.pmid: 17378581
references.citation: Biotechnol Bioeng. 2011 Dec;108(12):2823-34
references.pmid: 21702025
references.citation: Science. 2012 Nov 23;338(6110):1055-60
references.pmid: 23180856
references.citation: Biotechnol Biofuels. 2014 May 13;7:71
references.pmid: 24910713
references.citation: Biotechnol Biofuels. 2010 Mar 23;3:6
references.pmid: 20331857
references.citation: Appl Biochem Biotechnol. 2002 Spring;98-100:641-54
references.pmid: 12018289
references.citation: Appl Biochem Biotechnol. 2009 Dec;159(3):696-707
references.pmid: 19184544