Sugar substances (such as sugarcane juice and molasses), starchy mate­rials (such as wheat, corn, barley, potato, and cassava), and lignocellu — losic materials (such as forest residuals, straws, and other agricultural by-products) are being considered as the raw materials for ethanol pro­duction. The dominating sugars available or produced from these pop­ular raw materials are

■ Glucose, fructose, and sucrose in sugar substances

■ Glucose in starchy materials

■ Glucose from cellulose and either mannose or xylose from hemicel — lulose of lignocellulosic materials

Most ethanol-producing microorganisms can utilize a variety of hex — oses such as glucose, fructose, galactose, and mannose, and a limited number of disaccharides such as sucrose, lactose, cellobiose, and maltose, and rarely their polymers. Therefore, it is necessary to convert the com­plex polysaccharides, such as cellulose and starch, to simple sugars or disaccharides. Different types of substrates that need treatment are presented in Table 3.1, prior to fermentation.

In this section, sugar production from starchy materials is discussed; lignocellulosic materials are discussed in Sec. 3.5.