2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
- 35 -
Abstract
--This study focused on effects chemical and
physico-chemical pretreatments of
Abies grandis
wood on
enzymatic hydrolysis of cellulose into glucose in view of
potential applications in biofuel production. Wood particles
were treated with phosphoric acid, incubated in a hot water
bath at 50
o
C or they were submitted to microwave
irradiation. The highest glucose yields of up to 100% of
converted cellulose were reached by using 1 g of wood
particles in 8 ml of 80% phosphoric acid irradiated in a
microwave for 20 second and applying a combination of 4 U
ml
-1
cellulase, 4 U ml
-1
xylanase and 4 U ml
-1
laccase in 5 ml
of 50 mM sodium acetate buffer, pH 5.0 for cellulose
hydrolysis for 24 hrs. Evidence for the latter was given in
studies where glucose yields from cellulosic pellets obtained
from physico-chemical pretreatments were dramatically
increased when laccase was added to the samples prepared
for cellulose hydrolysis: generally, the combination of 4 U
ml
-1
cellulase, 4 U ml
-1
xylanase and 4 U ml
-1
laccase was
more effective in increasing glucose yields than 4 U ml
-1
cellulase and 4 U ml
-1
xylanase alone. Likely, laccase has a
potential to decrease inhibitory effects of phenolic
compounds present wood extractives on enzymatic
hydrolysis. Evidence for this was further given by
experiments where wood extractives or specific phenolic
compounds as found in wood extractives were added to
enzymatic reactions. Water extractives, and
p
-coumaric
acid, vanillic acid and ferulic acid in concentration-
dependent manner all inhibited the actions of cellulase on
carboxymethylcellulose (CMC). Addition of laccases in most
instances could partially or fully reverse the inhibitory
effects but in the case of ferulic acid. This compound in
presence of laccase or its products obtained by laccase-
mediated oxidation partially blocks cellulase activity,
possibly by chemical interactions (dimerization of cysteines,
cross-linking of tyrosines) on the cysteine and tyrosines-rich
cellulose-binding-motifs (CBMs) present in distinct
cellulases at the outmost C-terminal ends of the enzymes.
Index Terms
—
Biofuel, Chemical pretreatment, Physico-
chemical pretreatment, Microwave irradiation, Rate of
production of glucose, Kinetic curve of production of
glucose, influence of wood extractives, influence of phenolic
compound
I.
I
NTRODUCTION
Nowadays, much research has been performed and
more and more research concentrates on transforming
lignocellulose based on enzymatic hydrolysis to produce
bioethanol. Most efforts on the first generation of biofuels
have been focused on using biological resources that are
also used as food and fodder (such as sugarcane, cereals,
This work was supported by the Prince of Songkla University
(PSU), Thailand.
soybeans, seed from oil plants, animal fat) and this
development was induced by the various kinds of the
world’s demand and supply of energy consumption.
However, the first generation biofuel competes directly
with nourishing humans and animals. Therefore, these
resources are limited in available amounts. According to
this problematic [1, 2], the new (second) generation of
biofuels is targeted to use non-food and non-fodder
materials as substrates in enzymatic hydrolysis [3, 4, 5].
Straw and other agricultural residues as well as certain
fast growing grasses (e.g.
Miscanthus
) are established
biomaterials for second generation biofuels´ production
[6]. Much work has now also been carried out on using
e.g. hardwood trees from forests and plantations, such as
on wood of poplars and olive trees, respectively [7, 8, 9].
Less work has been invested into using softwood in
biofuel production [10].
A. grandis
wood is especially attractive because
A. grandis
is a fast growing coniferous tree with a high
potential for sustainable wood production and also
interesting applications in the wood products industries
[11, 12, 13, 14]. Moreover, as shown by the research in
this work, the renewable wood biomass from
A. grandis
is also a potential source for enzymatic treatment
technologies to unlock the energy stored in its
lignocellulose for transferring it into biofuels. In this
work, the
A. grandis
softwood has been explored using
different
pretreatment
methods
and
different
combinations of hydrolytic and oxidizing enzymes
(cellulase, xylanase,
β
-glucosidase, laccase) in wood
hydrolysis. The different pretreatments resulted in the
production of fermentable sugars from the wood cellulose
to possibly be used as a bio-base for fermentation
processes of bioethanol with e.g. suitable yeast [15, 16].
In the near future, process integration and optimization to
transform the whole wood of trees such as from
A. grandis
into value-added and biochemical products,
such as ethanol, but also butanol and other bio-based
chemicals such as lactic acid, succinic acid etc. could
become promising attempts to fulfill the world’s energy
consumption [17, 18].
The research presented here addresses new enzymatic
technologies as required if biofuels by environmentally
friendly production are to significantly contribute to
planetary energy needs and, with it, to the reduction of
greenhouse gas emission [19]. Next to other developing
technologies such as creating better yeast strains for sugar
conversion [16, 20], efficient hydrolysis protocols for
wood have to be established in finally enabling the
commercial viability of lignocellulosic ethanol [3, 4, 17].
Application of
Abies grandis
Wood for
Technical Use in Biofuel Production
B. Cherdchim*, A. Majcherczyk** and U. Kües**
* Faculty of Sciences and Industrial Technology, Prince of Songkla University, (
Thailand
)
** Division of Molecular Wood Biotechnology, Georg-August University of Göttingen, (
Germany
)
