*4.3.5. Ethanol*

Currently, the world has the prospect of a significant increase in demand for ethanol. The use of this fuel is concentrated on a global scale in power generation, in its mixture with gas‐ oline or simply dehydrated, being a considerable product in the global energy matrix [110].

*len tannophilus* DW06. For sugarcane straw, the ethanol production is only from cellulosic fraction. For example, Krishnan et al. [4] verified an ethanol production about 34–36 g/L us‐ ing the recombinant *S. cerevisiae* (424A LNH-ST) from the bagasse and straw pretreated by ammonia fiber expansion method (AFEX). Sindhu et al. [123] observed the ethanol produc‐ tion of 11.365 g/L using *S. cerevisae* yeast from leaves pretreated with dilute acid hydrolysis

Bioconversion of Hemicellulose from Sugarcane Biomass Into Sustainable Products

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29

Regarding the world ethanol scenario, a regular increase in the production has been ob‐ served (Figure 3). The Americas are the largest producer continent of ethanol. The United States of America is the largest producer country of ethanol with production levels over 51

Biobutanol, a four carbon primary alcohol (butyl alcohol-C4H10O), is second generation alco‐ holic fuel with a higher energy density and lower volatility as compared to ethanol in addi‐ tion to its existing applications as a solvent [126, 127]. The primary use of butanol is as an industrial solvent in the manufacturing of products such as lacquers and enamels. Butanol can be used directly in any gasoline engine without modification and/or substitution, be‐ cause it has several similar characteristics to gasoline, besides being compatible with ethanol blending may improve the blending of gasoline with ethanol [128]. It can be produced through processing of domestically grown crops, such as corn and sugar beets, and other

followed by enzymatic saccharification with cellulases.

**Figure 3.** World Annual Ethanol Production since 2006 (Source:[125]).

*4.3.6. Butanol*

biomass residues [128].

billion liters (13.5 U.S. gallons) in 2011 [124].

The first generation ethanol production consists in conversion of hexose sugars to ethanol, and it is relatively simple and usually performed in three steps: acquisition of fermentable sugars, fermentation of sugars by microorganisms and separation and purification of etha‐ nol, usually carried out by distillation, rectification and dehydration [111]. Microorganisms such as *Saccharomyces cerevisiae* consumes directly the sucrose present in sugarcane juice pro‐ ducing ethanol. However, in the long scenario, the use of juice or molasses to produce etha‐ nol will not be able to supply the increasing demand.

Biofuels from renewable sources, such as second generation ethanol production from ligno‐ cellulosic materials (bagasse and straw), may represent a sustainable alternative to environ‐ mental and social problems caused due to the extensive use of fossil fuels [112]. The process for second generation ethanol requires three steps: pretreatment of lignocellulosic materials, to make the hemicellulose sugars and cellulose more accessible, fermentation of sugars and separation and purification of ethanol [111]. Although it is an eminent perspective, the de‐ velopment of this technology requires some additional challenges. The production of etha‐ nol from lignocellulosic biomass can increase the productivity of ethanol per hectare of sugar cane planted [113], without increasing the cultivated area in the same proportions, not competing with food production for land use [112].

*S. cerevisiae* is the most common microorganism used for ethanol production from hexose sugars, but it is unable to produce ethanol from pentoses such as xylose. Among the micro‐ organism that can assimilate pentose sugars such as xylose, yeasts have shown more ethanol yield and productivity than bacteria and fungi [114]. There are some naturally yeast which ferments xylose to ethanol, among them, *Pichia stipitis* [116] and *Candida shehatae* [117] are the most employed in bioprocess.

Considering the process for production of second generation ethanol, sugarcane bagasse is reported as one of most used lignocellulosic materials, and among the microorganisms used for xylose conversion, *P. stipitis* yeast (taxonomic classification has been changed to *Scheffer‐ somyces stipitis* [118]) is widely used. For example, from sugarcane bagasse hemicellulosic hydrolysate, Canilha et al. [119] reported 7.5 g/L, 0.30 g/g and 0.16 g/L.h of ethanol produc‐ tion, yield and productivity, respectively, using hydrolysate treated with ion exchange res‐ ins as a medium of fermentation for ethanol production by *P. stipitis* DSM 3651 while Hande et al. [120] obtained 0.45 g/g using hydrolysate treated by neutralization and activated char‐ coal adsorption as a medium of fermentation for ethanol production by *Pichia* strain BY2. Other yeasts can be found in studies for ethanol production from sugarcane hemicellulosic hydrolysate. For example, Chandel et al. [121] observed maximum ethanol yield (0.48 g/g) from ion exchange detoxified hydrolysate followed by use activated charcoal, by *C. shehatae* NCIM 3501 and Cheng et al. [122] obtained 19 g/L ethanol, yield of 0.34 g/g and productivity of 0.57 g/L.h when used a batch culture with pretreated hydrolysate as substrate for *Pachyso‐* *len tannophilus* DW06. For sugarcane straw, the ethanol production is only from cellulosic fraction. For example, Krishnan et al. [4] verified an ethanol production about 34–36 g/L us‐ ing the recombinant *S. cerevisiae* (424A LNH-ST) from the bagasse and straw pretreated by ammonia fiber expansion method (AFEX). Sindhu et al. [123] observed the ethanol produc‐ tion of 11.365 g/L using *S. cerevisae* yeast from leaves pretreated with dilute acid hydrolysis followed by enzymatic saccharification with cellulases.

Regarding the world ethanol scenario, a regular increase in the production has been ob‐ served (Figure 3). The Americas are the largest producer continent of ethanol. The United States of America is the largest producer country of ethanol with production levels over 51 billion liters (13.5 U.S. gallons) in 2011 [124].

**Figure 3.** World Annual Ethanol Production since 2006 (Source:[125]).

#### *4.3.6. Butanol*

*4.3.5. Ethanol*

Currently, the world has the prospect of a significant increase in demand for ethanol. The use of this fuel is concentrated on a global scale in power generation, in its mixture with gas‐ oline or simply dehydrated, being a considerable product in the global energy matrix [110].

28 Sustainable Degradation of Lignocellulosic Biomass - Techniques, Applications and Commercialization

The first generation ethanol production consists in conversion of hexose sugars to ethanol, and it is relatively simple and usually performed in three steps: acquisition of fermentable sugars, fermentation of sugars by microorganisms and separation and purification of etha‐ nol, usually carried out by distillation, rectification and dehydration [111]. Microorganisms such as *Saccharomyces cerevisiae* consumes directly the sucrose present in sugarcane juice pro‐ ducing ethanol. However, in the long scenario, the use of juice or molasses to produce etha‐

Biofuels from renewable sources, such as second generation ethanol production from ligno‐ cellulosic materials (bagasse and straw), may represent a sustainable alternative to environ‐ mental and social problems caused due to the extensive use of fossil fuels [112]. The process for second generation ethanol requires three steps: pretreatment of lignocellulosic materials, to make the hemicellulose sugars and cellulose more accessible, fermentation of sugars and separation and purification of ethanol [111]. Although it is an eminent perspective, the de‐ velopment of this technology requires some additional challenges. The production of etha‐ nol from lignocellulosic biomass can increase the productivity of ethanol per hectare of sugar cane planted [113], without increasing the cultivated area in the same proportions, not

*S. cerevisiae* is the most common microorganism used for ethanol production from hexose sugars, but it is unable to produce ethanol from pentoses such as xylose. Among the micro‐ organism that can assimilate pentose sugars such as xylose, yeasts have shown more ethanol yield and productivity than bacteria and fungi [114]. There are some naturally yeast which ferments xylose to ethanol, among them, *Pichia stipitis* [116] and *Candida shehatae* [117] are

Considering the process for production of second generation ethanol, sugarcane bagasse is reported as one of most used lignocellulosic materials, and among the microorganisms used for xylose conversion, *P. stipitis* yeast (taxonomic classification has been changed to *Scheffer‐ somyces stipitis* [118]) is widely used. For example, from sugarcane bagasse hemicellulosic hydrolysate, Canilha et al. [119] reported 7.5 g/L, 0.30 g/g and 0.16 g/L.h of ethanol produc‐ tion, yield and productivity, respectively, using hydrolysate treated with ion exchange res‐ ins as a medium of fermentation for ethanol production by *P. stipitis* DSM 3651 while Hande et al. [120] obtained 0.45 g/g using hydrolysate treated by neutralization and activated char‐ coal adsorption as a medium of fermentation for ethanol production by *Pichia* strain BY2. Other yeasts can be found in studies for ethanol production from sugarcane hemicellulosic hydrolysate. For example, Chandel et al. [121] observed maximum ethanol yield (0.48 g/g) from ion exchange detoxified hydrolysate followed by use activated charcoal, by *C. shehatae* NCIM 3501 and Cheng et al. [122] obtained 19 g/L ethanol, yield of 0.34 g/g and productivity of 0.57 g/L.h when used a batch culture with pretreated hydrolysate as substrate for *Pachyso‐*

nol will not be able to supply the increasing demand.

competing with food production for land use [112].

the most employed in bioprocess.

Biobutanol, a four carbon primary alcohol (butyl alcohol-C4H10O), is second generation alco‐ holic fuel with a higher energy density and lower volatility as compared to ethanol in addi‐ tion to its existing applications as a solvent [126, 127]. The primary use of butanol is as an industrial solvent in the manufacturing of products such as lacquers and enamels. Butanol can be used directly in any gasoline engine without modification and/or substitution, be‐ cause it has several similar characteristics to gasoline, besides being compatible with ethanol blending may improve the blending of gasoline with ethanol [128]. It can be produced through processing of domestically grown crops, such as corn and sugar beets, and other biomass residues [128].

Production of butanol by using fermentation to replace the chemical process depends large‐ ly on the availability of inexpensive and abundant raw materials and efficient bioconversion of these materials. The producers strains of biobutanol which have been extensively studied are *Clostridium sp.* [126, 127] and genetically engineered *E. coli* [129, 130]. Studies to deter‐ mined the recovery of biobutanol from fermentation broth (dry corn and wet corn milling) whey permeate and molasses) by distillation showed that it was not economical when com‐ pared with butanol derived from the current petrochemical route [131]. The use of lignocel‐ lulosic substrates in combination with developed process technologies is expected to make the production of biobutanol economically viable [132].

For replacement of the conventional plastic, biodegradable plastic is a feasible option. How‐ ever, it is necessary that the price of biopolymers should be competitive [148]. The cost of production is directly linked to the type of microorganism and the substrate employed. The strain used should have a high specific growth rate, using low cost substrates and a high conversion factor of substrate in PHA [144]. The selection of the proper raw material for bio‐ polymer production has an additional impact on the ecological pressure of the entire proc‐ ess [148]. Renewable sources of polymeric materials offer an answer for sustainable

Bioconversion of Hemicellulose from Sugarcane Biomass Into Sustainable Products

http://dx.doi.org/10.5772/53832

31

Sugarcane biomass represents an enormous reserve of renewable carbon source, which has the potential to be utilized as a feedstock for the production of biodegradable polymers. For instance, using sugarcane bagasse hydrolysate, Yu and Stahl [151] investigated the simulta‐ neous detoxification and PHA production by the bacterium *Ralstonia eutropha* and accumu‐ lated PHA at a rate of 57 wt% of cell mass despite the large index of inhibitors. Silva et al. [152] studied the biopolymer production by *Burkholderia cepacia* IPT 048 and *B. sacchari* IPT 101 from sugarcane bagasse hydrolysate and obtained polymer contents and yields reached, respectively, 62% and 0.39 g/g with strain IPT 101 and 53% and 0.29 g/g with strain IPT 048.

To create a balance between food versus fuel production from lignocellulosic residues, ade‐ quate land use, judicious usage of grain and corn/cane crop residues is essential [153]. Math‐ ews et al. [153] presented a sugarcane 'feed+fuel' biorefinery model, which produces bioethanol and yeast biomass, a source of single-cell protein (SCP), that can be used as a high-protein animal feed supplement. The yeast SCP, which is synthesized as a part of the process of producing cellulosic bioethanol from sugarcane can be used as a supplement for grass in the feed of cattle grazing on pasture and thereby potentially release land for in‐

The production of SCP by growing microorganisms on organic wastes and its use in animal feed has a long history. Protein as an animal feed supplement has long been viewed as a potentially very significant development, with much discussion devoted to the topic of mi‐ crobial SCP since the 1970s. The grounds for the intense interest in SCP is that feedstocks, in the form of agricultural and organic wastes are plentiful, and the rate of growth of microor‐ ganisms producing SCP is prodigious. Whereas a soybean crop is harvested after 1 season of growth, microorganisms double their cell mass within hours [154]. According to Tanaka et al. [155] the production of single-cell protein (SCP) from lignocellulosic materials needs four steps: (1) physical and chemical pretreatments; (2) cellulase production; (3) enzymatic hy‐ drolysis; and (4) assimilation or fermentation of holocellulose. For each step the following topics need to be considerate: (1) effect and mode of action of each pretreatment; (2) optimi‐ zation of culture media and operating conditions, and application of mutation, protoplast fusion and gene recombination; (3) elucidation of kinetics of cellulase reaction, and methods of immobilization, stabilization and recovery of cellulases; and (4) examples of SCP produc‐ tion by several types of cultivation and treatment of lignin. According to Zadrazil et al. [156] in order to convert a lignocellulosic material to obtain a more nutritive product, it is necessa‐

creased sugarcane production, with minimal land use change effects.

development of economically and ecologically attractive technology [149, 150].

*4.3.9. Single cell protein*

#### *4.3.7. Butanediol*

2,3-Butanediol (2,3-BDL), also known as 2,3-butylene glycol, is a valuable chemical feed‐ stock because of its application as a solvent, liquid fuel, and as a precursor of many synthet‐ ic polymers and resins. One of its well known applications is the formation of methyl ethyl ketone, by dehydration, which can be used as a liquid fuel additive [8].

Butanediol is produced during oxygen-limited growth, by a fermentative pathway known as the mixed acid-butanediol pathway [133]. The 2,3-BDL pathway and the relative propor‐ tions of acetoin and butanediol serve to maintain the intracellular NAD/NADH balance un‐ der changed culture conditions. All of the sugars commonly found in hemicellulose and cellulose hydrolysates can be converted to butanediol, including glucose, xylose, arabinose, mannose, galactose, and cellobiose. The theoretical maximum yield of butanediol from sug‐ ar is 0.50 kg per kg. With a heating value of 27,200 J/g, 2,3-BDL compares favorably with ethanol (29,100 J/g) and methanol (22,100 J/g) for use as a liquid fuel and fuel additive [134]. Hexose and pentose can be converted to 2,3-BDL by several microorganisms including *Kleb‐ siella* [135], *Aeromonas* [136], *Bacillus* [137], *Paenibacillus* [138], *Serratia*, *Aerobacter* [139] and *Enterobacter* [140].

#### *4.3.8. Biopolymers*

The use of plastics is consistently increasing in the society due to its advantages such as low cost and durability, and the replacement of conventional materials such as paper and glass [141]. However, these materials have xenobiotic and recalcitrant nature, having an extreme‐ ly long degradation rate [142, 143]. Besides its slow degradation, the accumulation of plastic is a major risk to marine animals. When is landfilled, is more difficult to occurs the process of decomposition and when it is incinerated, causes the release of several toxic compounds [144]. Due to the increasing demand of plastics and its incorrect disposal, these materials have become a major environmental problem. An alternative to trying to solve this rising problem is the replacement of conventional plastics for biodegradable plastics. Biodegrada‐ ble plastics are natural biopolymers that are synthesized and catabolized by microorganisms and are made from renewable resources and do not lead to the depletion of finite resources [145, 146]. Among bioplastics, polyhydroxyalkanoates (PHA) and polylactates (PLA) got significant attraction. The PHA's are typically accumulated by bacterial via intra or extracel‐ lular while PLA is produced by polymerizing lactic acid via microbial fermentation [147].

For replacement of the conventional plastic, biodegradable plastic is a feasible option. How‐ ever, it is necessary that the price of biopolymers should be competitive [148]. The cost of production is directly linked to the type of microorganism and the substrate employed. The strain used should have a high specific growth rate, using low cost substrates and a high conversion factor of substrate in PHA [144]. The selection of the proper raw material for bio‐ polymer production has an additional impact on the ecological pressure of the entire proc‐ ess [148]. Renewable sources of polymeric materials offer an answer for sustainable development of economically and ecologically attractive technology [149, 150].

Sugarcane biomass represents an enormous reserve of renewable carbon source, which has the potential to be utilized as a feedstock for the production of biodegradable polymers. For instance, using sugarcane bagasse hydrolysate, Yu and Stahl [151] investigated the simulta‐ neous detoxification and PHA production by the bacterium *Ralstonia eutropha* and accumu‐ lated PHA at a rate of 57 wt% of cell mass despite the large index of inhibitors. Silva et al. [152] studied the biopolymer production by *Burkholderia cepacia* IPT 048 and *B. sacchari* IPT 101 from sugarcane bagasse hydrolysate and obtained polymer contents and yields reached, respectively, 62% and 0.39 g/g with strain IPT 101 and 53% and 0.29 g/g with strain IPT 048.
