Polysaccharides of Starchy and Lignocellulose Materials and their Use in Ethanol Production: Enzymes and other Factors Affecting the Production Process

Background and Objective: Nowadays, production of ethanol involves many kinds of plant based materials, from conventionally used starchy materials such as rye, wheat, corn and barley to lignocellulose materials serving in second-generation bioethanol production. While raw materials containing simple sugars do not require such complex mashing processes, starchy and lignocellulose materials need significant processing. This review provides an in-depth description of the structures of starchy raw materials commonly used in production of first-generation ethanol. Furthermore, the review describes the structure of lignocellulose biomasses used for second-generation bioethanol production. Results and Conclusion: Methods commonly used in distilleries to release starch from plant raw materials belong to pressure-thermal pretreatments known as steaming or pressureless liberation of starch methods. Literature shows that amylolysis is strongly determined by the morphology of starch granules. The larger the specific surface area of granules, the greater their susceptibility to amylolysis. The key stage in preparation of starch raw materials for fermentation is starch hydrolysis, which consists of two steps of liquefaction and saccharification. Several species of bacteria (e.g. Bacillus licheniformis) and fungi (e.g. Aspergillus niger) are available that are capable of producing enzymes necessary for starch hydrolysis. Enzymes needed for starch hydrolysis are divided into 1) liquefying enzymes such as α-amylase produced by Aspergillus niger and Bacillus licheniformis or can be found in malt and 2) saccharifying enzymes such as glucoamylase, β-amylase and maltogenic α-amylase of fungal, bacterial and malt origins. Proteases and phytases are used to support mashing process hydrolases of non-starch polysaccharides (xylanase and pullulanase).