**4.2. Methods of detoxification of hemicellulosic hydrolysates**

When the lignocellulosic matrix is breakdown by different types of pretreatments, particu‐ larly by dilute acid process, undesired compounds that are toxic for microbial metabolism are liberated and/or formed in addition of sugars. These products can be divided into three groups according to their origin: derived from sugars (furfural and 5-hydroxymethylfurfu‐ ral), lignin derivatives (phenolics i.e. vanillin, *p*-hydroxybenzaldehyde, lignans, etc.) and weak acids (acetic, formic and levulinic) [53]. Several studies have shown that these byprod‐ ucts generated during the hydrolysis of the hemicellulose fraction from different materials affect negatively the microbial metabolism, hindering the conversion of sugars in some products of interest [53, 54, 55].

Several chemical, physical and biological methods have been used for removing these by‐ products present in the hemicellulosic hydrolysates. Some detoxification methods as well as their advantages and disadvantages are summarized in the Table 4.

#### **4.3. Products from hemicellulose**

*Process Advantages Disadvantages*

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





Hemicel.: hemicellulosic fraction; Cel.: cellulosic fraction; X: solubilized fraction by the pretreatment

**Table 3.** Advantages and disadvantages of different methods of pretreatment





Biological Pretreatments

Hemicellulose differs substantially from cellulose to be amorphous, which makes it more easily hydrolyzed than cellulose [49]. The hemicellulosic fraction reaches 40% of lignocellu‐ losic material and acts as substance of reserve and support. This fraction presents branched structure composed by pentoses (D-xylose and L-arabinose), hexoses (D-galactose, D-man‐ nose and D-glucose) and small amounts of acetic and uronic (D-glucuronic, D-4-O-methyl‐ glucuronic and D-galacturonic acids) acids [8, 21]. Other sugars such as L-rhamnose and L-

Ozonolysis

Organosolv

Wet Oxida‐ tion

> Microor‐ ganism

the ozone incorporates conjugated double bonds and functional groups with high elec‐ tron densities

simultaneous process of hydrolyses and de‐ lignification catalyzed by solvents and diluted acid solution

occurs in the presence of oxygen or catalyzed air, sodium carbonate is the preferred catalyst

modification of the chemical composition and/or structure of lignocellulosic materials employing microorgan‐ isms

**4. Hemicellulosic fraction**

**4.1. Structure of hemicellulose**

*Solubilized Fraction*

*Hemicel. Cel. Lignin*

X X

X X [9]

X

ess <sup>X</sup>

*References*

[45] [46]

[47] [48]

[15] [38] [44]

> Hemicelluloses have a wide variety of applications. They can be hydrolyzed into hexo‐ ses (glucose, galactose, and mannose) and pentoses (xylose and arabinose), can be transformed into fuel ethanol and other value-added products such as 5-hydroxyme‐ thylfurfural (HMF), xylitol, ethanol, butanediol, butanol, etc. In addition, hemicelluloses also can be converted into various biopolymers, like polyhydroxyalkanoates (PHA) and polylactates (PLA).

> In industrial applications, hemicelluloses are used to control water and the rheology of aqueous phases. Thus, they may be used as food additives, thickeners, emulsifiers, gel‐ ling agents, adhesives and adsorbents [71]. According to Peng et al. [72], hemicellulo‐ ses have also been investigated for their possible medical uses such as ulcer protective [73], antitussive [74], immunostimulatory [75] and antitumor properties [76]. For exam‐ ple, xylooligosaccharides have been shown to have economic utilization in the pharma‐ ceutical industry for applications such as treating viral and cancer processes in the human body [77, 78].

Arabinoxylans are used as emulsifiers, thickeners, or stabilizers in the food, cosmetic, or pharmaceutical industries. Glucomannans are used in the food industry (as caviar substitu‐ ent), whereas arabinogalactans have applications in the mining (for processing of iron and copper ores) or pharmaceutical industry (as a tablet binder or emulsifier). 4-O-methylglu‐

Bioconversion of Hemicellulose from Sugarcane Biomass Into Sustainable Products

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

25

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

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

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

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

curonoxylan is a water absorption agent and also presents antitumor activity [71].

purification steps, xylose is recovered of purified media by crystallization [84].

other products such as acetone, amino acids, antibiotics, enzymes and hormones [85].

industry for the preparation of HMF because of its price lower than fructose [89].

*4.3.2. 5-Hydroxymethylfurfural and levulinic acid*

*4.3.1. Xylose and glucose*

levulinic acid [86].


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

Arabinoxylans are used as emulsifiers, thickeners, or stabilizers in the food, cosmetic, or pharmaceutical industries. Glucomannans are used in the food industry (as caviar substitu‐ ent), whereas arabinogalactans have applications in the mining (for processing of iron and copper ores) or pharmaceutical industry (as a tablet binder or emulsifier). 4-O-methylglu‐ curonoxylan is a water absorption agent and also presents antitumor activity [71].
