Journal of Advances in Microbiology

Fermentable sugars are crucial in bioethanol production, as they serve as the primary substrate for microbial fermentation, while microorganisms like yeast convert these sugars into ethanol and other byproducts like carbon dioxide. There is a need to break down complex carbohydrates into fermentable sugars, the process begins with pretreatment. Pretreatment is a crucial step in bioethanol production, particularly when using starchy materials and lignocellulosic biomass. Substrate is prepared by such pretreatment for efficient enzymatic hydrolysis and subsequent fermentation. The primary goal of pretreatment is to disrupt the complex structure of starch, cellulose, hemicellulose and lignocellulosic materials, making them more accessible to enzymes that break them down into fermentable sugars. This is achieved by methods that remove lignin, increase surface area, and modify the crystallinity of cellulose. Therefore, the aim of this research was to review substrate and its treatment for efficient bio-ethanol production by microorganisms. Fermentable feedstock, starchy substrate, saccharification of starch with enzymes such as alpha-amylase, beta-amylase and gamma-amylase were reviewed. Moreover, hemicellulose substrates, lignocellulosic biomass and chemical pretreatment of lignocellulosic substrates, such as acid hydrolysis and alkaline hydrolysis with the formation of fermentation inhibitors during hydrolysis, were discussed. Mechanical pretreatment of lignocellulosic substrate using irradiation, thermal energy, gases, and finally biological pretreatment using lignolytic fungi were mentioned. In conclusion, for optimal bioethanol production, there is a need for substrate pretreatment, especially where complex carbohydrates are involved, but the method should be exploited to avoid production of inhibitors that could negatively impact enzymatic hydrolysis or fermentation process.