title: Comparison of enzymatic reactivity of corn stover solids prepared by dilute acid, AFEX™, and ionic liquid pretreatments.
abstract: BACKGROUND
  Pretreatment is essential to realize high product yields from biological conversion of naturally recalcitrant cellulosic biomass, with thermochemical pretreatments often favored for cost and performance. In this study, enzymatic digestion of solids from dilute sulfuric acid (DA), ammonia fiber expansion (AFEX™), and ionic liquid (IL) thermochemical pretreatments of corn stover were followed over time for the same range of total enzyme protein loadings to provide comparative data on glucose and xylose yields of monomers and oligomers from the pretreated solids. The composition of pretreated solids and enzyme adsorption on each substrate were also measured to determine. The extent glucose release could be related to these features.
  
  
  RESULTS
  Corn stover solids from pretreatment by DA, AFEX, and IL were enzymatically digested over a range of low to moderate loadings of commercial cellulase, xylanase, and pectinase enzyme mixtures, the proportions of which had been previously optimized for each pretreatment. Avicel® cellulose, regenerated amorphous cellulose (RAC), and beechwood xylan were also subjected to enzymatic hydrolysis as controls. Yields of glucose and xylose and their oligomers were followed for times up to 120 hours, and enzyme adsorption was measured. IL pretreated corn stover displayed the highest initial glucose yields at all enzyme loadings and the highest final yield for a low enzyme loading of 3 mg protein/g glucan in the raw material. However, increasing the enzyme loading to 12 mg/g glucan or more resulted in DA pretreated corn stover attaining the highest longer-term glucose yields. Hydrolyzate from AFEX pretreated corn stover had the highest proportion of xylooligomers, while IL produced the most glucooligomers. However, the amounts of both oligomers dropped with increasing enzyme loadings and hydrolysis times. IL pretreated corn stover had the highest enzyme adsorption capacity.
  
  
  CONCLUSIONS
  Initial hydrolysis yields were highest for substrates with greater lignin removal, a greater degree of change in cellulose crystallinity, and high enzyme accessibility. Final glucose yields could not be clearly related to concentrations of xylooligomers released from xylan during hydrolysis. Overall, none of these factors could completely account for differences in enzymatic digestion performance of solids produced by AFEX, DA, and IL pretreatments.
authors.affiliation: BioEnergy Science Center (BESC), Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA ; Department of Chemical and Environmental Engineering, Bourns College of Engineering, University of California (UCR), Riverside, CA 92521, USA ; Center for Environmental Research and Technology (CE-CERT), Bourns College of Engineering, University of California, Riverside, CA 92507, USA.
authors.forename: Xiadi
authors.initials: X
authors.lastname: Gao
authors.affiliation: BioEnergy Science Center (BESC), Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA ; Center for Environmental Research and Technology (CE-CERT), Bourns College of Engineering, University of California, Riverside, CA 92507, USA.
authors.forename: Rajeev
authors.initials: R
authors.lastname: Kumar
authors.affiliation: Deconstruction Division, Joint BioEnergy Institute (JBEI), Emeryville, CA 94608, USA ; Sandia National Laboratories, Livermore, CA 94551, USA.
authors.forename: Seema
authors.initials: S
authors.lastname: Singh
authors.affiliation: Deconstruction Division, Joint BioEnergy Institute (JBEI), Emeryville, CA 94608, USA ; Sandia National Laboratories, Livermore, CA 94551, USA.
authors.forename: Blake A
authors.initials: BA
authors.lastname: Simmons
authors.affiliation: DOE Great Lakes Bioenergy Research Center (GLBRC), Michigan State University, East Lansing, MI 48824, USA ; Biomass Conversion Research Laboratory, Department of Chemical Engineering and Materials Science, Michigan State University, 3815 Technology Boulevard, MBI Building, Lansing, MI 48910, USA.
authors.forename: Venkatesh
authors.initials: V
authors.lastname: Balan
authors.affiliation: DOE Great Lakes Bioenergy Research Center (GLBRC), Michigan State University, East Lansing, MI 48824, USA ; Biomass Conversion Research Laboratory, Department of Chemical Engineering and Materials Science, Michigan State University, 3815 Technology Boulevard, MBI Building, Lansing, MI 48910, USA.
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Dale
authors.affiliation: BioEnergy Science Center (BESC), Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA ; Department of Chemical and Environmental Engineering, Bourns College of Engineering, University of California (UCR), Riverside, CA 92521, USA ; Center for Environmental Research and Technology (CE-CERT), Bourns College of Engineering, University of California, Riverside, CA 92507, USA.
authors.forename: Charles E
authors.initials: CE
authors.lastname: Wyman
keywords: Cellulase; Corn stover; Enzyme adsorption; Hydrolysis; Oligomers; Pretreatment