Saccharification Fermentation and Process Integration

Abstract

The biomass pretreatment is followed by the next step, i.e., saccharification or hydrolysis, meant for the breakdown of carbohydrate polymers into fermentable sugars. Enzymatic hydrolysis of cellulose is a non-chemical method based on microbial lignocellulolytic enzymes. The hydrolysis of cellulose and hemicellulose can be carried out by highly specific carbohydrate-active enzymes, known as glycosyl hydrolases enzymes. The enzymes of cellulase complex vary in their substrate specificity, site of action, and mechanism of cellulose depolymerization. The cellulases are generated certainly by a wide array of microorganisms from both eukaryotic (fungi) and prokaryotic (eubacteria and actinomycetes) domains. The rate of enzymatic cellulolysis is governed by several parameters such as substrate loading, enzyme loading, the efficacy of preceding pretreatment in altering substrate characteristics, efficiency and activity of cellulases, hydrolysis conditions including mixing, pH temperature, and reaction time. The rate of enzymatic hydrolysis of cellulose is also affected by the performance of enzymes which are inhibited by their end products such as glucose and cellobiose accumulated in the reaction mixture with the progress of the process. The technology for cellulosic ethanol has not been commercialized yet. Various strategies are known which have the potential to improve the cellulases for bioethanol production. The simplest strategy involves tapping relatively unexplored habitats for the search of novel cellulolytic microbes. Thus, significant improvements can be made to enhance the in-house production of cellulases as an effort to reduce the cost of enzymes in biomass saccharification. Techno-economic evaluation in future can reveal the price reductions attainable through on-site production of enzymes.