*4.3.1. Xylose and glucose*

**Process Advantages Disadvantages References**


> - high cost - selective removal of inhibitors







[56] [57]

[58] [59]

[59] [60] [61] [62]

[63]

[60] [64] [65]

[66] [67]

[68]

[56] [59] [69] [70]

Physical Methods


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


Physic-Chemical Methods


> - precipitate toxic compounds




Biological Methods


**Table 4.** Advantages and disadvantages of different detoxification methods of hemicellulosic hydrolysate

Evaporation/ Concentration

Membrane

Ion Exchange Resin

Overlimming

Activated Charcoal

Extraction with Organic Solvents

Vegetable Polymer

Microorganism

removes toxic compounds by evaporation in a vacuum concentrator based on the volatility

membranes have surface functional groups attached to their internal pores, which may eliminate metabolic inhibitors

resins change undesirable ions of the liquid phase to be purified by saturating of functional groups of resins

increase of the pH followed by reduction

adsorption of toxic compounds by charcoal which is activated to increase the contact surface

mix of liquid phase to be purified and a organic solvent. The liquid phase is recovered by separation of two phases (organic and aqueous)

biopolymers are composed by tannins with astringent properties that flocculate inhibitors compounds

specific enzymes or microorganisms that act on the inhibitors compounds present in hydrolysates and change their composition

The D-xylose (C5H10O5) is the main carbohydrate found in the hemicellulose fraction of sug‐ arcane bagasse and straw. It is used as a sweetener for diabetics [79], as non-cariogenic sweetener [80], to enhance the flavor of food made from beef and poultry [81], to prepare marinades and baked [81] and as substrate in fermentation processes to produce different products, such as penicillin, biodegradable polymers and xylitol [50, 82]. Monomeric xylose from hemicellulose has a selling price of ~\$1.2/kg [83]. It is known that in industrial scale, xylose is obtained from lignocellulosic materials rich in xylan. These materials are hydro‐ lyzed in the presence of dilute acids. Then, the hemicellulose hydrolysates are purified, in order to remove the byproducts generated during the hydrolysis of hemicellulose. After the purification steps, xylose is recovered of purified media by crystallization [84].

D-glucose is also found in the hemicellulose fraction of sugarcane bagasse and straw and can be obtained by hydrolysis of cellulosic materials. Some compounds that are obtained from glu‐ cose fermentation are alcohols (ethanol, isopropanol, butanol, 2,3-butanediol, glycerol), car‐ boxylic acids (acetic acid, propanoic acid, lactic acid, gluconic acid, malic acid, citric acid) and other products such as acetone, amino acids, antibiotics, enzymes and hormones [85].

#### *4.3.2. 5-Hydroxymethylfurfural and levulinic acid*

5-Hydroxymethylfurfural (HMF) (C5H4O2), which is derived from the hexoses (6-carbon sugars) present in the hemicellulose, is produced by steam treatment followed by dehydra‐ tion [85, 86, 87]. HMF is an intermediate in the production of levulinic acid from 6-carbon sugars in the biofinery process. HMF is very useful not only as intermediate for the produc‐ tion of the biofuel, dimethylfuran (DMF) and other molecules, but also for important mole‐ cules such as levulinic acid, 2,5-furandicarboxylic acid (FDA), 2,5-diformylfuran (DFF), dihydroxymethylfuran and 5-hydroxy-4-keto-2-pentenoic acid [88]. Glucose is still utilized in industry for the preparation of HMF because of its price lower than fructose [89].

Levulinic acid (4-oxopentanoic acid) (C5H8O3) is a valuable platform chemical due to its spe‐ cific properties. It has two highly reactive functional groups that allow a great number of synthetic transformations. Levulinic acid can react as both a carboxylic acid and a ketone. The carbon atom of the carbonyl group is usually more susceptible to nucleophilic attack than that of the carboxyl group. Due to the spatial relationship of the carboxylic and ketone groups, many of the reactions proceed, with cyclisation, to form heterocyclic type molecules (for example methyltetrahydrofuran). Levulinic acid is readily soluble in water, alcohols, es‐ ters, ketones and ethers. The worldwide market has estimated the price of \$ 5/kg for pure levulinic acid [86].

#### *4.3.3. Furfural and formic acid*

Furfural (2-furaldehyde) and its derivatives, furfuryl alcohol, furan resins, and tetrahydro‐ furan, are produced in many countries from corn cobs, wheat and oat hulls, and many other biomass materials [90]. Furfural, which is derived from the pentoses (five-carbon sugars) present in hemicellulose, is produced by steam treatment followed by dehydration with hy‐ drochloric or sulfuric acid [87, 90]. The market price of furfural was approximately \$1/kg compared with prices in 1990 of \$1.74/kg for furfural and \$1.76/kg for furfuryl alcohol [83, 86]. The most important furfuryl alcohol is used to produce furan resins for foundry sand binders. Tetrahydrofuran is made by the decarbonylation of furfural with zinc-chromiummolybdenum catalyst followed by hydrogenation. It is also made by the dehydration of 1,4 butanediol [87]. Other uses for furfural, such as production of adiponitrile, might be found if furfural prices were reduced by expanded production [90].

the chemical production such as the use of high temperature and pressure in the process and the purification steps with low efficiency and productivity [52]. In this context, the bio‐ technological production of xylitol from hemicellulosic hydrolysates is a promising process with great economic interest. This process can add value to the lignocellulosic residues, like sugarcane bagasse and straw, promoting a complete utilization of these materials, using the cellulosic and hemicellulosic fractions to obtain xylitol and others value-added bioproducts [98]. Among the microorganisms that produce xylitol, yeast, particularly the genus *Candida, Pichia, Debaryomyces* are the most employed due to their ability to convert xylose to xylitol, with significant yields [99]. Xylitol can be produced through microbial transformation reac‐ tions by yeast from D-xylose, or by both yeast and bacteria from D-glucose [100]. D-xylose can also be directly converted into xylitol by NADPH-dependent xylose reductase [101].

Bioconversion of Hemicellulose from Sugarcane Biomass Into Sustainable Products

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

27

Considering xylose fermentation by yeasts, the main factors that should be controlled are: sub‐ strate concentration, cellular concentration, the presence of inhibitors, aeration flow, adapta‐ tion of the microorganism to the hydrolysate, temperature and pH [102, 103]. It can be found many works in the literature where these factors were studied extensively using the hemicellu‐ losic hydrolysates obtained from different lignocellulosic materials. From sugarcane bagasse hemicellulosic hydrolysate, for example, Carvalho et al. [61] reported the production of 19.2 g/L of xylitol by *Candida guilliermondii*; Santos et al. [104] achieved 18 g/L of xylitol with a bio‐ conversion yield of 0.44 g/g employing a fluidized bed reactor operated in semi-continuous mode with the same yeast; and recently, Prakash et al. [105] produced xylitol, with a yield and volumetric productivity of 0.69 g/g and 0.28 g/L.h, respectively, using *Debaryomyces hansenii*.

The world xylitol production exceeds 10,000 tons per year and is directed mainly to the food, pharmaceutical and cosmetics [106]. The American xylitol market is estimated at \$159 million for 2012 while it expected \$400 million to \$500 million for global market [107]. From the Figure 2, it can be seen the average annual prices of xylitol from 1995 to 2007. Xylitol price has decreased over last decades until 2007 (Figure 2), however since 2009, the price of

**Figure 2.** Xylitol price profile from 1995 to 2007 (Source: adapted from reference [109]).

xylitol has increased to \$4-5/kg [108].

Formic acid (methanoic acid) is an important organic chemical which is widely used in in‐ dustries. Recently, it received renewed attraction to be used as environmentally benign stor‐ age and transportation medium for hydrogen, the clean energy in future. Extensive studies have shown that hydrogen and CO2 could be quickly and efficiently generated by the de‐ composition of formic acid by hydrothermal reaction or catalyst reaction. Also, some re‐ searchers have demonstrated that formic acid has the potential to direct power fuel cells for electricity generation and automobiles [91]. It is used extensively as a decalcifier, as an acid‐ ulating agent in textile dyeing and finishing, and in leather tanning. It is also used in the preparation of organic esters and in the manufacture of drugs, dyes, insecticides, and refrig‐ erants. Formic acid can also be converted to calcium magnesium formate which can be used as a road salt. The current market price of formic acid is \$0.16/liter [86].

#### *4.3.4. Xylitol*

Xylitol is a polyol of five carbons (C5H12O5) easily found in nature in many fruits and plants. Among them, the yellow plum is the vegetable that contains highest level of xylitol [92]. This polyol is an intermediate metabolite in the carbohydrate metabolism in mammals, with an endogenous production followed by assimilation of 5-15g per day in a normal adult. Xy‐ litol is widely used as a sweetener by diabetics due to its slow adsorption and entrance in pathways which is independent of the insulin and does not contribute in rapid change of blood glucose levels [93].

This polyol, with anti-cariogenic properties, is employed in foods, dental applications, medi‐ cines and surfactants [94, 95]. In the dental applications, the use of xylitol reduces the saliva‐ ry flow, reduce gingivitis, stomatitis and lesions to poorly fitted dentures. If used in toothpaste, its action enhances the action of sodium fluoride and chlorhexidine, increasing the concentrations of xylitol 5-P [96]. For human diet, the Food and Drug Administration classifies this product as "GRAS" - "Generally Recognized as Safe" [97].

At large scale, xylitol is produced by chemical reduction of xylose derived mainly of wood hydrolysates. This process consists in steps of acid hydrolysis of the vegetal material, hydro‐ lysate purifications and crystallization of xylitol [92]. However, there are disadvantages in the chemical production such as the use of high temperature and pressure in the process and the purification steps with low efficiency and productivity [52]. In this context, the bio‐ technological production of xylitol from hemicellulosic hydrolysates is a promising process with great economic interest. This process can add value to the lignocellulosic residues, like sugarcane bagasse and straw, promoting a complete utilization of these materials, using the cellulosic and hemicellulosic fractions to obtain xylitol and others value-added bioproducts [98]. Among the microorganisms that produce xylitol, yeast, particularly the genus *Candida, Pichia, Debaryomyces* are the most employed due to their ability to convert xylose to xylitol, with significant yields [99]. Xylitol can be produced through microbial transformation reac‐ tions by yeast from D-xylose, or by both yeast and bacteria from D-glucose [100]. D-xylose can also be directly converted into xylitol by NADPH-dependent xylose reductase [101].

*4.3.3. Furfural and formic acid*

*4.3.4. Xylitol*

blood glucose levels [93].

furfural prices were reduced by expanded production [90].

as a road salt. The current market price of formic acid is \$0.16/liter [86].

classifies this product as "GRAS" - "Generally Recognized as Safe" [97].

Furfural (2-furaldehyde) and its derivatives, furfuryl alcohol, furan resins, and tetrahydro‐ furan, are produced in many countries from corn cobs, wheat and oat hulls, and many other biomass materials [90]. Furfural, which is derived from the pentoses (five-carbon sugars) present in hemicellulose, is produced by steam treatment followed by dehydration with hy‐ drochloric or sulfuric acid [87, 90]. The market price of furfural was approximately \$1/kg compared with prices in 1990 of \$1.74/kg for furfural and \$1.76/kg for furfuryl alcohol [83, 86]. The most important furfuryl alcohol is used to produce furan resins for foundry sand binders. Tetrahydrofuran is made by the decarbonylation of furfural with zinc-chromiummolybdenum catalyst followed by hydrogenation. It is also made by the dehydration of 1,4 butanediol [87]. Other uses for furfural, such as production of adiponitrile, might be found if

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

Formic acid (methanoic acid) is an important organic chemical which is widely used in in‐ dustries. Recently, it received renewed attraction to be used as environmentally benign stor‐ age and transportation medium for hydrogen, the clean energy in future. Extensive studies have shown that hydrogen and CO2 could be quickly and efficiently generated by the de‐ composition of formic acid by hydrothermal reaction or catalyst reaction. Also, some re‐ searchers have demonstrated that formic acid has the potential to direct power fuel cells for electricity generation and automobiles [91]. It is used extensively as a decalcifier, as an acid‐ ulating agent in textile dyeing and finishing, and in leather tanning. It is also used in the preparation of organic esters and in the manufacture of drugs, dyes, insecticides, and refrig‐ erants. Formic acid can also be converted to calcium magnesium formate which can be used

Xylitol is a polyol of five carbons (C5H12O5) easily found in nature in many fruits and plants. Among them, the yellow plum is the vegetable that contains highest level of xylitol [92]. This polyol is an intermediate metabolite in the carbohydrate metabolism in mammals, with an endogenous production followed by assimilation of 5-15g per day in a normal adult. Xy‐ litol is widely used as a sweetener by diabetics due to its slow adsorption and entrance in pathways which is independent of the insulin and does not contribute in rapid change of

This polyol, with anti-cariogenic properties, is employed in foods, dental applications, medi‐ cines and surfactants [94, 95]. In the dental applications, the use of xylitol reduces the saliva‐ ry flow, reduce gingivitis, stomatitis and lesions to poorly fitted dentures. If used in toothpaste, its action enhances the action of sodium fluoride and chlorhexidine, increasing the concentrations of xylitol 5-P [96]. For human diet, the Food and Drug Administration

At large scale, xylitol is produced by chemical reduction of xylose derived mainly of wood hydrolysates. This process consists in steps of acid hydrolysis of the vegetal material, hydro‐ lysate purifications and crystallization of xylitol [92]. However, there are disadvantages in

Considering xylose fermentation by yeasts, the main factors that should be controlled are: sub‐ strate concentration, cellular concentration, the presence of inhibitors, aeration flow, adapta‐ tion of the microorganism to the hydrolysate, temperature and pH [102, 103]. It can be found many works in the literature where these factors were studied extensively using the hemicellu‐ losic hydrolysates obtained from different lignocellulosic materials. From sugarcane bagasse hemicellulosic hydrolysate, for example, Carvalho et al. [61] reported the production of 19.2 g/L of xylitol by *Candida guilliermondii*; Santos et al. [104] achieved 18 g/L of xylitol with a bio‐ conversion yield of 0.44 g/g employing a fluidized bed reactor operated in semi-continuous mode with the same yeast; and recently, Prakash et al. [105] produced xylitol, with a yield and volumetric productivity of 0.69 g/g and 0.28 g/L.h, respectively, using *Debaryomyces hansenii*.

The world xylitol production exceeds 10,000 tons per year and is directed mainly to the food, pharmaceutical and cosmetics [106]. The American xylitol market is estimated at \$159 million for 2012 while it expected \$400 million to \$500 million for global market [107]. From the Figure 2, it can be seen the average annual prices of xylitol from 1995 to 2007. Xylitol price has decreased over last decades until 2007 (Figure 2), however since 2009, the price of xylitol has increased to \$4-5/kg [108].

**Figure 2.** Xylitol price profile from 1995 to 2007 (Source: adapted from reference [109]).
