**1. Introduction**

Second-generation biofuels from lignocellulosic materials have gained much attention since the lignocelluloses are not in competition with food sources and animal feed and will pro‐ vide a new sustainable energy sources alternative to petroleum-based fuels (Galbe and Zac‐ chi, 2007). Bioethanol production from herbaceous lignocellulose such as corn stover (Ryu and Karim, 2011), rice straw (Ko *at al*., 2009), sweet sorghum bagasse (Cardoba *et al*., 2010), switchgrass (Keshwani and Cheng, 2009), bamboo (Sathitsuksanoh *at al*., 2010), wheat straw (Talebnia *et al*., 2010), alfalfa stems (González-García *at al*., 2010), and silvergrass (Guo *et al.*, 2008) has been extensively developed through a variety of processes combining the biologi‐ cal saccharification and fermentation steps with the pre-treatment methods. In almost all processes, the pretreatments to remove the lignin components and to promote an enzymatic digestibility of cellulosic components are carried out by the use of energy and cost which are frequently higher than those of bio-fuels gained (Alvira *et al*., 2010). If lignocelluloses with low lignin-content are selected, the operation to remove the lignin might be excluded from the bio-ethanol process.

Among the many kinds of lignocelluloses, therefore, we (Yasuda *et al*., 2011; Yasuda *et al*., 2012) and other groups (Li *et a*l., 2011; Brandon *et al*., 2011; Zhang *et a*l., 2011; Huang *et al*.,

© 2013 Yasuda et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Yasuda et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

2011; Lin *et al*., 2011a; Lin *et al*., 2010b; Kai *et al.*, 2010; Anderson *et al*., 2008) have been inter‐ ested in napiergrass (*Pennisetum purpureum* Schumach) which is herbaceous lignocellulose with its low lignin- content. During our investigations on bioethanol production, it was found that the alkali-pretreatment of napiergrass enhances scarcely the ethanol yield where‐ as the alkali-pretreatment of silvergrass (*Miscanthus sinensis* Anderss) remarkably enhances the ethanol yield (Yasuda *et al*., 2011). Here, we compared the effectiveness of lignin-remov‐ al between napiergrass and other lingocelluloses with different lignin-contents (rice straw, silvergrass, and bamboo) in order to evaluate the availability of non-pretreated napiergrass as the raw materials of bio-ethanol.

defined as 10,000 units when two sheets of filter papers (1 cm×1 cm) degraded at pH 5.0 and 45 °C by the cellulase for 150 min. The filter papers were entirely degraded in 114 min by 10 mg of Acremozyme. Thus, cellulase activity of Acremozyme was determined to be 1320 units mg–1 according to the following equation: cellulase activity (units mg–1) = 150×10,000/ (a×b) where a and b denoted weight of cellulase in mg and period in min required for the

Effectiveness of Lignin-Removal in Simultaneous Saccharification and Fermentation for Ethanol Production from

Napiergrass c) 57.3 (37.5 : 26.5) 14.9 12.7 15.1 Rice straw 61.3 (39.7 : 28.4) 18.2 17.7 2.8 Silvergrass 41.0 (34.2 : 11.4) 21.7 4.0 33.3 Bamboo 66.5 (43.9 : 30.0) 26.2 1.4 5.9

b) The values in the parenthesis are the amounts (g) of hexose and pentose derived from 100 g of lignocelluloses.

The saccharification of the powdered cellulosic materials (10.0 g) was performed with Acre‐ mozyme (1.0 g) in an acetate buffer (60 mL, pH 5.0) under vigorous shaking at 45 °C. At the given saccharification time, the portion was taken from the reaction mixture and centrifuged at 12,000 rpm. The supernatant solutions were subjected to analysis for saccharides. The amounts of the reducing saccharides obtained from the saccharification reactions at 30, 40,

*Saccharomyces cerevisiae* NBRC 2044 was grown at 30 ºC for 24 h in a basal medium (initial pH 5.5) consisting of glucose (20.0 g L–1), peptone (1.0 g L–1, Difco), yeast extract (1.0 g L–1), NaHPO4 (1.0 g L–1), and MgSO4 (3.0 g L–1). After incubation for 24 h, the cell suspension of *S. cerevisiae* was obtained. The grown culture of *S. cerevisiae* showed a cell density of 7.7×107

The suspension of cellulosic materials (1.33 g) in an acetate buffer solution (5 mL, pH 5.0) was introduced into the test tube (100 mL) and was autoclaved at 121 ºC for 20 min. After cooling the autoclaved suspension of cellulosic materials, the cell suspension (0.16 mL) of *S. cerevisiae* and the Acremozyme cellulase (133 mg) in an acetate buffer solution (3 mL, pH 5.0) were added (Yasuda *et al*., 2012). The glucan contents were determined to be 436, 475, 410, and 525 mg in non-treated cellulosic materials (1.33 g) of napiergrass, rice straw, silvergrass, and bamboo, respectively. In the case of alkali-treated cellulosic materials (1.33 g), 761 (na‐

**Holocellulose (hexose : pentose) b)**

a) The amounts of components derived from 100 g of lignocellulose.

**2.3. Simultaneous Saccharification and Fermentation (SSF)**

**Table 1.** Components of herbaceous lignocellolosic materials

**Components/g a)**

Napiergrass, Rice Straw, Silvergrass, and Bamboo with Different Lignin-Contents

**Lignin Ash Others**

http://dx.doi.org/10.5772/54194

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degradation, respectively.

c) Referred from Yasuda *et al*., 2012.

and 45 °C were almost the same.

cells mL–1.

**Lignocelloloses**
