Bioconversion of agro-industrial residues to second-generation bioethanol

Abstract

Bioenergy is the term used for energy produced from lignocellulosic biomass. Most of the residues produced from agricultural and industrial activities present high levels of lignocellulose. They are mostly formed by rigid structures mainly containing hemicellulose and cellulose intermixed by lignin. These macromolecules are linked by covalent and hydrogen bonds, thus forming a complex architecture, which give a great resistance to their hydrolysis. This hampers the subsequent production of fermentable sugars and their fermentation to produce second-generation bioethanol. The technologies to obtain second-generation bioethanol, independent of the plant source, involve the hydrolysis of polysaccharides from the biomass in order to generate sugars that can be fermented by yeasts. This chapter addresses the importance of biomass for the production of green fuels. In this chapter, the potential of different lignocellulosic biomasses, especially the agricultural crop residues, is described. The composition of the main molecules forming the cell wall of different plants is provided. The enzymes that are involved in the deconstruction of plant cell walls as well as the release of fermentable sugars are discussed. The pretreatment and fermentation of biomass for the second-generation ethanol production by yeasts are described. Some challenges concerning the technologies are considered, but, on the other hand, some alternatives are also pointed out.