17.1 Introduction

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along with lignin ([C9H10O3(OCH3)0.9−1.7]x), and an insignificant quantity of

proteins, ash, pectin, and other compounds [8]. Studies so far have revealed that cel-

lulose, hemicellulose, and lignin contents account to 30–60%, 20–40%, and 15–25%

of dry weight of LCB, respectively [9]. Cellulose is the major structural subunit of

LCB. It is a linear polysaccharide with β-(1, 4)-glycosidic bonds linking individual

subunits of D-glucose [10]. It is soluble in water when the pH is drastically low or

high but easily miscible with N-methylmorpholine-N-oxide (NMMO) as well as

ionic liquids (ILs) [11]. Cellulose is biocompatible, structurally stable, hydrophilic,

possesses reactive hydroxyl group which makes it suitable for the manufacture of

fibers, films, composites, fuels, and high value chemicals [12]. Hemicellulose is the

second constituent of LCB, composed of various polysaccharides, some of which

include arabinoxylan, galactomannan, glucomannan, glucuronoxylan, xylan, and

xyloglucan. These polysaccharides are present in the form of short chains, linked

by β-(1,4)- or β-(1,3) glycosidic bonds [13]. Cellulose and hemicellulose exhibit

decreased levels of polymerization and are non-crystalline in nature; therefore,

they can easily degrade to monosaccharides and are considered commercially

important [14]. Lignin acts as a protecting barrier by covalently bonding to other

subunits of LCB which enhances its recalcitrance. The complex three-dimensional

structure shows cross-linked polymers of phenyl propane that are bound to each

other by carbon–carbon (5–5, β–β) and aryl-ether bonds (β-O-4, α-O-4). The poly-

mers are known to be altered when the methoxyl groups located on the aromatic

rings are substituted. For example, the three key units of lignin are guaiacyl (G),

p-hydroxyphenyl (H), and syringyl (S) [15].

17.1.4

Challenges in Bioethanol Production from LCB

Ethanol which is derived from LCB is one of the most preferred fuel candidates in

the present world. Not only this, but also biomass obtained from ethanol can act as

a precursor to the different materials that are currently obtained from sources that

are unsustainable. But, the drawback of this novel concept is that the treatment cost

for ethanol is higher which hinders the process to be commercially replicable and

profitable. Several technologies are coming up to give rise to high product yields

with overall low cost [1]. Bioethanol is one of the renewable sources along with

eco-friendly characteristics which is a promising alternative to fossil fuels. Although

practically ethanol is created from edible sources, LCB has attracted a lot of attention

lately. In any case, the transformation efficiency of the biomass varies enormously

concerning the origin furthermore, nature of LCB, essentially because of the variety

in lignocellulosic composition. The two polysaccharides in LCB, cellulose and hemi-

cellulose, are firmly connected to lignin and make a lignocellulosic network that is

exceptionally vigorous and difficult to depolymerize. To introduce LCBs into com-

mercial ethanol creation, ongoing exploration endeavors have been dedicated to the

techno-monetary upgrades of the general change process [2].

The main objective of the book chapter is to study the potential role of different

microorganisms and efficiency in enhancing bioethanol production from LCB as a

substrate.