Biotechnology for Zero Waste – Emerging Waste Management Techniques (Chaudhery Mustansar Hussain (editor) etc.)

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Enzyme Technology for the Degradation of Lignocellulosic

Waste

Swarrna Haldar and Soumitra Banerjee

Visvesvaraya Technological University, Centre for Incubation, Innovation, Research and Consultancy (CIIRC),

Jyothy Institute of Technology, Department of Food Technology, Off Kanakapura Road, Thathaguni,

Bangalore, 560082, India

10.1

Introduction

Among all plants, cereal plants contribute to nearly 75% of lignocellulosic waste.

Cereal straw alone accounts for 2.9 billion tonnes per annum. Maximum residue is

produced from sugarcane as bagasse, stalk, leaves, press mud, etc. which are wasted

[1]. Cellulose, hemicellulose, and lignin are the primary lignocellulosic components,

along with some proteins and phenolic polymers.

Nowadays, many countries are producing “First-generation bioethanol” by

fermenting starch or sucrose obtained from the food grains wheat, corn, and

sugarcane. The growing demand for bioethanol is increased to 100 billion liters in

2020 [2]. However, reduction in the production cost for bioethanol can be achieved

by using the non-food substrates like lignocellulosic materials for the production of

“second-generation ethanol.” This second-generation ethanol can be blended with

fossil fuels to produce biofuels [3].

The plant cell wall polysaccharides mainly consist of cellulose, hemicellulose,

pectin, and the phenolic polymer, lignin. Together, they give structural integrity,

strength, and complexity to the cell wall [3]. Cellulose forms a linear polymeric

chain consisting of 8000–12 000 D-glucose units linked by β-1,4-glycosidic bond.

Microfibrils are highly insoluble structures which exist as bundles in the crystalline

form of cellulose. The non-crystalline structure, i.e. the amorphous region, is

found within the microfibrils [4]. The second rich polysaccharide present in

the cell wall is hemicellulose, which is a heterogeneous polysaccharide. The

structural backbone of hemicellulose contains many heteropolymers like xylan,

galactomannan, glucuronoxylan, arabinoxylan, glucomannan, and xyloglucan.

In the cereals and hardwood, xylan is most prevalent, while in the softwood,

glucomannan is the most abundant polymer of hemicelluloses [5, 6]. Pectin is a

heteropolysaccharide with α-1,4-linked D-galacturonic acid forming the backbone.

It has two regions viz. the smooth region containing D-galacturonic acids which

can undergo acetylation or methylation and the hairy region containing both

Biotechnology for Zero Waste: Emerging Waste Management Techniques, First Edition.

Edited by Chaudhery Mustansar Hussain and Ravi Kumar Kadeppagari.