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Bioethanol: Market and Production Processes 73

3.4 Production of Sugars
from Raw Materials
Sugar substances (such as sugarcane juice and molasses), starchy mate-
rials (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 pro-
duction. The dominating sugars available or produced from these pop-
ular 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 com-
plex 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.

3.4.1 Sugar solution from starchy
materials
There are various raw materials that contain starch and are suitable
for ethanol production. Corn is the most widely used on an industrial
scale for this purpose. However, there are several other cereals, such as
wheat, rye, barley, and sorghum, and crop roots such as potato and cas-
sava, which are used as raw materials for ethanol production. The cereals
contain about 60–70% starch, 8–12% proteins, 10–15% water, and small

TABLE 3.1 Treatment for Different Types of Substrates
Pretreatment Hydrolysis or
Substrate or liquefaction saccharification Detoxification

Potential sugar No No Typically no
substrates
Starchy materials Yes Yes No
Lignocellulose Yes Yes Depends on the
materials hydrolysis method