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17 Utilization of Microbial Potential for Bioethanol Production from Lignocellulosic Waste

17.3.3.4

Versatile Peroxidase (VP)

Versatile peroxidase (VP) (EC 1.11.1.16) possesses catalytic activities of both MnP

and LiP. Hence, effectively oxidize both phenolic and non-phenolic aromatic com-

pounds. Like MnP, it is able to oxidize Mn²⁺ and have high-redox potential. VP

is used in conjunction with other microbial peroxidases including MnP and LiP

to degrade non-phenolic aromatic compounds, such as the breakdown of veratyl

alcohol or veratryl glycerol β-guaiacyl ether to veratraldehyde, and the decomposi-

tion of p-dimethoxybenzene to p-benzoquinone. The enzyme is found in different

strains of Bjerkandera sp. and Pleurotus sp. and mediates oxidation of variety of

substrates including substituted phenols, plant peroxidase hydroquinone’s, and the

bulky, recalcitrant lignin, directly without redox mediators, the property makes it a

suitable catalyst for pretreatment processes.

17.4

Enzymatic Hydrolysis

Cellulose along with hemicellulose within the LCBs is converted to fermentable

sugars through a procedure known as hydrolysis [41]. In view of the pretreatment

strategy, hemicellulose might either be totally hydrolyzed into monomeric sugars

and changed into ethanol in due course of fermentation, or it could be changed

into oligosaccharides on experience of inadequate depolymerization furthermore,

require hydrolysis before exposure to fermentation. The predominant molecules in

hemicelluloses are xylose found in hardwoods and mannose found in softwoods and

alongside a limited quantity of arabinose and galactose [40]. Indeed, in spite of the

fact that a little segment of cellulose may likewise be changed over into glucose, a

large portion of this mass still stays unreacted [42].

Enzymatic hydrolysis incorporates the preparation procedures that helps in con-

version of the starch molecules into monomeric sugars. Cellulases at pH of 4.5 and

temperature of 50^∘are generally required. A few proteins like swollenin become

vital toward the release of the cellulosic fibrils from the cellulose molecule in a

non-hydrolytic manner, without acting upon the β-(1,4) glycosidic bonds. The cel-

lulose conglomerations are therefore scattered by the swollenin, resulting a higher

accessibility of cellulases to the cellulose chains [31].

The enzymatic hydrolysis is dependent on how accessible cellulose is to the

cellulase enzyme, as well as the viability of cellulose. A significant body of research

pointed toward a concrete association between the adsorption of the compound

and the speed of hydrolysis. The expulsion of xylan, with respect to the evacuation

of lignin, affects the activity of cellulases on cellulose. Although xylan or lignin

evacuation improves saccharification rate, the xylan expulsion legitimately affects

glucan chain reaction. Henceforth, expulsion of xylan is better than expulsion of

lignin. Expulsion of xylan helps in decreased compound restraint by xylo-oligomers

just as decreased necessities of frill enzymes. Cellulose is the most abundant poly-

mer of glucose. Its specific structure favors the polymer chains to be firmly stuffed

that are insoluble and impervious to depolymerization [20]. The other segment of

LCB incorporates hemicelluloses, an extended polymer of glucose subbed along