Pretreatments and Factors Affecting Saccharification and Fermentation for Lignocellulosic Ethanol Production

Lignocellulosic biomass can be utilized to produce ethanol, a promising alternative energy source for sustainable energy production and has the potential to be a valuable substitute. Various pretreatment techniques change the physical and chemical structures of the lignocellulosic biomass and improve the hydrolysis rate. The cost of ethanol production from lignocellulosic material is relatively high based on current pretreatment technologies and the main challenges are low yield and high cost of the hydrolysis process. Considerable research efforts have been made to improve the hydrolysis of lignocellulosic biomass. There are many factors involved in the enzymatic hydrolysis (saccharification) and fermentation of lignocellulosic biomass. In this review, different kinds of pretreatment and factors affecting enzymatic saccharification and fermentation in the industrial ethanol production are highlighted for the development of ethanol production in the future. Thermomechanical extrusion, particle-size reduction, and alkaline pretreatments are potential pretreatments for lignocellulosic ethanol production. Crystallinity index, lignin and hemicellulose contents, and degree of polymerization are the main factors affecting enzymatic saccharification. Total phenolic content and furfural mainly affect fermentation. Protein digestibility and free amino nitrogen are the essential nutrients for yeast during fermentation.