Lignocellulosic biomass represents a vast supply of fermentable carbohydrates
and functional aromatic compounds. Conversion of lignocellulosics to ethanol and other
useful products would be of widespread economical and environmental benefit. Better
understanding of the behavior of different lignicellulosic feedstocks in fermentation
protocols as well as catalytic activities involved in lignocellulosic depolymerization will
further enhance the commercial viability of biomass-to-ethanol conversion processes.
The relative toxicity of the combined non-xylose components in prehydrolysates
derived from three different lignocellulosic biomass feedstocks (poplar, corn stover and
switchgrass, or Panicum virgatum L.) was determined using a Pichia stipits fermentation
assay. The relative toxicity of the prehydrolysates, in decreasing order, was poplar-derived
prehydrolysates > switchgrass-derived prehydrolysates > corn stover-derived
prehydrolysates. Ethanol yields averaged 74%, 83% and 88% of control values for
poplar, switchgrass and corn stover prehydrolysates, respectively. Volumetric ethanol
productivities (g ethanol l⁻¹ h⁻¹) averaged 32%, 70% and 102% of control values for
poplar, switchgrass and corn stover prehydrolysates, respectively. Ethanol productivities
correlated closely with acetate concentrations in the prehydrolysates; however, regression lines correlating acetate concentrations and ethanol productivities were found to be
feedstock-dependent.
Differences in the relative toxicity of xylose-rich prehydrolysates derived from
woody and herbaceous feedstocks are likely due to the relative abundance of a variety of
inhibitory compounds, e.g. acetate and aromatic comounds. Fourteen aromatic monomers
present in prehydrolysates prepared from corn stover, switchgrass, and poplar were
tentatively identified by comparison with published mass spectra. The concentrations of
the aromatic monomers totaled 112, 141 and 247 mg(l)⁻¹ for corn stover, switchgrass and
poplar prehydrolysates, respectively. The woody and herbaceous feedstocks differed in
both amount and type of aromatic monomers.
The cellulases of Trichoderma reesei are the most widely studied for use in the
depolymerization of lignocellulosics. The Trichoderma cellobiohydrolases CBH1 and
CBH2 are traditionally categorized as exo-acting cellulases. A simple individual-based
model was created to explore the potential effects of native endo activity on substratevelocity
profiles. The model results indicate that an enzyme with a small amount of endo
activity will show an apparent substrate inhibition as substrate levels are increased.
Actual hydrolysis studies using affinity chromatography-purified CBH2 preparations
from three laboratories indicate that CBH2 has native endo activity, while CBH1 does
not. / Graduation date: 1999
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/27269 |
| Date | 30 June 1998 |
| Creators | Fenske, John J. |
| Contributors | Penner, Michael H. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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