Enzymes for the Degradation of Biomass

Enzymatic hydrolysis in a biorefinery process plays a key role in the conversion of lignocellulosic biomass into sugars, which in turn are used as substrates for fermentation into chemicals or fuels. This chapter focuses on the wide range of lignocellulose degrading enzymes like cellulases, hemicellulases, pectinases, and ligninases. These enzymes vary in their substrate as well as their mode of action, which will be shown exemplarily for cellulases. The role these enzymes play in the biorefinery process, also necessary background information about lignocellulosic biomass, and possible pretreatment methods are given. Section 15.1 describes the composition of lignocellulose from cellulose, hemicellulose, and lignin and its influence on hydrolysis. Cellulose is degraded by fungal secreted cellulases into the monomer glucose (Sect. 15.2), while hemicellulose and lignin are degraded by hemicellulases and ligninases (Sect. 15.3). The choice of a suitable enzyme cocktail depends on the composition of the biomass, which in turn depends on the pretreatment processes (Sect. 15.4). Finally, special challenges are highlighted using the example of an ethanol biorefinery (Sect. 15.5).