**3. Methods of separation of hemicellulose from cellulignin complex**

The lignocellulosic materials are renewable resources which can be used to obtain sus‐ tainable products as well as value-added biomolecules [31]. However, cellulose, hemicel‐ lulose and lignin are arranged to form a highly recalcitrant structure [32], hindering the availability of carbohydrates for fermentation processes, representing a high barrier for the bioconversion of lignocellulosic materials [33]. Through a pretreatment process, the biomass components can be separated, releasing fermentable sugars such as xylose, ara‐ binose and glucose and making the cellulose more accessible to the action of cellulolytic enzymes [34, 35]. This step is one of the most expensive step of biomass processing, thus, studies to lower the cost are extremely important [35].

According to Brodeur et al. [36], the typical characteristics that must be attained in a pre‐ treatment process are: production of highly digestible solids that enhances sugar yields during enzyme hydrolysis; avoid the degradation of sugars; minimize the formation of inhibitors; recover the lignin for conversion into valuable co-products. Pretreatment proc‐ ess should be cost effective and environment friendly. All these features are considered in order that pretreatment results balance against their impact cost on downstream proc‐ essing steps and the trade-off with operational cost, capital cost and biomass cost [37]. The pretreatments methods can be divided into physical, chemical, physic-chemical and biological [38]. Some methods of pretreatments as well as their advantages and disadvan‐ tages are shown in the Table 3.

Different types of biomass (woody plants, grasses, agricultural crops, etc) has different contents and proportions of cellulose, hemicellulose and lignin which determine the di‐ gestibility of the biomass [37]. There is not a universal pretreatment process for all bio‐ mass. Depending on the process and conditions used, hemicellulose sugars may be degraded to weak acids, furan derivates and phenolics that inhibit the fermentation proc‐ ess, leading to lower yields and productivities of the desired product [8]. Thus, the meth‐ od of pretreatment used will depend on the type of raw material used, the objective of the process (the constituent to be degraded) and the product to be obtained, which will directly affect the cost benefit.


From the technological viewpoint, sugars that are present in the cellulosic (glucose) and hemicellulosic (xylose, arabinose, glucose, mannose and galactose) fractions representing the substrates that can be used in fermentative process for production of some sustaina‐ ble products such as xylitol, butanediol, single cell protein, ethanol and xylitol. However, the close association between the three major fractions (cellulose, hemicellulose and lig‐ nin) of the lignocelulosic materials, like bagasse and straw, causes difficulties for the re‐ covery of these substrates in the form of monomers with high purity. Therefore, to use these three constituents it is required a selective separation of each fraction by pretreat‐ ment techniques, delignification and hydrolysis, involving the breakdown of hemicellu‐

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

**3. Methods of separation of hemicellulose from cellulignin complex**

thus, studies to lower the cost are extremely important [35].

The lignocellulosic materials are renewable resources which can be used to obtain sus‐ tainable products as well as value-added biomolecules [31]. However, cellulose, hemicel‐ lulose and lignin are arranged to form a highly recalcitrant structure [32], hindering the availability of carbohydrates for fermentation processes, representing a high barrier for the bioconversion of lignocellulosic materials [33]. Through a pretreatment process, the biomass components can be separated, releasing fermentable sugars such as xylose, ara‐ binose and glucose and making the cellulose more accessible to the action of cellulolytic enzymes [34, 35]. This step is one of the most expensive step of biomass processing,

According to Brodeur et al. [36], the typical characteristics that must be attained in a pre‐ treatment process are: production of highly digestible solids that enhances sugar yields during enzyme hydrolysis; avoid the degradation of sugars; minimize the formation of inhibitors; recover the lignin for conversion into valuable co-products. Pretreatment proc‐ ess should be cost effective and environment friendly. All these features are considered in order that pretreatment results balance against their impact cost on downstream proc‐ essing steps and the trade-off with operational cost, capital cost and biomass cost [37]. The pretreatments methods can be divided into physical, chemical, physic-chemical and biological [38]. Some methods of pretreatments as well as their advantages and disadvan‐

Different types of biomass (woody plants, grasses, agricultural crops, etc) has different contents and proportions of cellulose, hemicellulose and lignin which determine the di‐ gestibility of the biomass [37]. There is not a universal pretreatment process for all bio‐ mass. Depending on the process and conditions used, hemicellulose sugars may be degraded to weak acids, furan derivates and phenolics that inhibit the fermentation proc‐ ess, leading to lower yields and productivities of the desired product [8]. Thus, the meth‐ od of pretreatment used will depend on the type of raw material used, the objective of the process (the constituent to be degraded) and the product to be obtained, which will

lose-lignin-cellulose complex [21].

tages are shown in the Table 3.

directly affect the cost benefit.


fucose may also be present in small amounts. Xylose is the main carbohydrate present in the

Bioconversion of Hemicellulose from Sugarcane Biomass Into Sustainable Products

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

23

The heterogeneous structure of hemicellulose with a low polymerization degree makes it in‐ teresting fraction for fermentation process. The open three-dimensional conformation of hemicellulose favors the diffusion of the catalyst in the molecule, providing a better yield of

The hemicellulosic fraction can be removed of lignocellulosic materials by some type of pre‐ treatments, summarized in the Table 3, liberating sugars, mainly xylose, that subsequently can be fermented to sustainable products such as xylitol, butanediol, single cell protein and

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

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

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

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

hemicellulosic fraction, representing about 80% of total sugars [35, 50].

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

their advantages and disadvantages are summarized in the Table 4.

hydrolysis in mild conditions [51, 52].

products of interest [53, 54, 55].

**4.3. Products from hemicellulose**

polylactates (PLA).

human body [77, 78].

ethanol [24, 27].

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