Production of ethanol
from cellulosic biomass using enzymes was first carried out in1980s by US
Department of Energy. While enzymatic hydrolysis of cellulose display several
advantages like higher yield, lower energy cost, higher selectivity and mild
operating conditions, it was judged that the technology was too risky for
industry to pursue at that time. Later, advancement in biotechnology reduced processing
costs making cellulosic ethanol competitive. Lignocellulose makes up about half
of the matter produced by photosynthesis and is considered as an attractive source of
bioenergy and bio-based chemicals. It is composed of cellulose, hemicellulose
and lignin that are strongly intermeshed and chemically bonded by covalent and non-covalent
forces. Besides these some
other materials such as proteins, pectin and ash are present in very lesser quantity. The proportion of
cellulose, hemicellulose and lignin varies depends on the source of origin. Forestry,
agriculture, pulp/paper industry and municipal solids are the main source of
lignocellulose biomass. Although a vast amount of lignocellulose are produced,
only a small portion are used in value added products, such as ethanol, food
additives, organic acids, enzymes, and pharmaceutical building blocks, rest
being considered waste. These valuable materials were treated as waste in many countries
in the past and still are today in some developing counties, which raises many
environmental concerns.

Hydrolysis of lignocellulose
into simple sugars can be achieved either enzymatically by cellulolytic enzymes
or chemically by sulfuric or other acids. Although enzymatic hydrolysis displayed
several advantages over acid hydrolysis since it entails lesser energy and mild
environmental conditions with generation of fewer fermentation inhibitors but
seems to be a bottleneck due to the high costs of enzyme production. Therefore,
a continuous efforts have been made for cost effective production and search
for new sources of enzymes. The
complex structure of lignocellulose make it very recalcitrant for enzymatic
degradation. Besides structural complexity of lignocellulose some enzymes can
be absorbed by condensed lignin which decreases hydrolysis yield by
non-specific linkages of these enzymes.

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