Lignocellulosic biomass is the most abundant and inexpensive
material for bioethanol production. Bioethanol is a sustainable
and renewable transportation fuel that is a promising substitute
to gasoline and represents an environment-friendly fuel because
it reduces the amount of greenhouse gas emissions, which have
been ascribed as a major cause of global warming. Much of the
bioethanol produced in the world is currently derived from sugar
or starchy crops. However, production of bioethanol requires the
development of an economically feasible and sustainable process
utilizing renewable lignocellulosic materials that do not compete
with food sources [1]. Lignocellulose composed of cellulose, hemicellulose
and lignin has hydrolytic stability and is not readily
broken down into fermentable sugars. The cellulose and hemicellulose
are polysaccharides that can be hydrolyzed to hexose
and pentose sugars, whereas the lignin which is a phenol compound
cannot be used for ethanol production. A major bottleneck
in the biomass-to-ethanol conversion is the cost of enzymatic
hydrolysis of the biomass, which includes the use of enzymes such
as cellulases. Although enzymatic hydrolysis has several advantages
over acid hydrolysis, such as lowering the environmental
impact and reducing the by-product yields