Applications of hemicelluloses

Potential of hemicellulose in the pharmaceutical field could potentially be developed as drug formulation excipients such as binders, disintegrator, thickeners, and stabilizers. In addition, applications of hemicellulose have been done by making the derivatives that have pharmacological effects such as lowering cholesterol and inhibitors of HIV [26-28,41, 57]. 

Only recently have new processes been developed where biomass components are separated and isolated. Access to hemicelluloses on the pilot scale opens a new world of applications of hemicelluloses as materials. A new generation of plastics, coatings, hydrogels, and so on based on this renewable resource is waiting to be discovered. We are convinced that the hemicelluloses will play an important role in moving society from its petrochemical dependency into a sustainable economy. 

The structural characteristics, such as the construction of the backbone and the type and degree of branching, affect the physical properties of polymers, e.g. solubility, viscosity and crystallinity. Thus it is foreseen that the development of more efficient utilization and novel applications of hemicelluloses require targeted tailoring of their properties. 

The classical applications of hemicelluloses are shown in Fig. 7.4, which shows its use in specialty chemicals, solvents as well as biodegradable polymers (the latter being a recent addition). This section seeks to highlight the applications... 

Publications pertaining to applications of hemicellulose, such as the xylans, have recently started to appear in the open literature. After starch production from com, the com hulls can be used to produce a highly branched heteroxylan, which has applications as a new food gum (Hromadkova and Ebringerova, 1995 Saulnier et al, 1998). The possibility of using xylan (in levels of 0-40% wt/wt)... 

Most biotechnological applications of hemicellulose utilize acid and/or solvent-based hydrolysates, in which the native xylan is cleaved to xylose and xylose oligomers. This saccharification can be achieved through such chemical means, but also by physical and/or enzymatic methods. Forest biomass is often treated with dilute acid or enzymatic hydrolysis as a pretreatment for fermentative application of the hemicellulosic fraction. Dilute acid hydrolysis generally uses low concentrations of mineral acids (H2SO4, HCl, 2-5%) at high temperatures (e.g. 150-170 °C) and pressures (10 atm) (Sun and Cheng, 2002). Concentrated... 

In the past, research activities in the field of hemicellulose were aimed mainly at utilizing plant biomass by conversion into sugars, chemicals, fuel and as sources of heat energy. However, hemicelluloses, due to their structural varieties and diversity are also attractive as biopolymers, which can be utilized in their native or modified forms in various areas, including food and non-food applications. 

From recent literature it is known that the disintegration of lignified cell walls can be achieved by steam explosion treatments resulting in solubilization of partially depolymerized hemicelluloses [91,92]. The application of this method on wheat bran yielded feruloylated GAX with different feruUc acid content [93]. Partly depolymerized water-soluble, acetylated AGX was obtained from spruce wood by employing microwave treatment [94]. 

Ebringerova, A. (2005). Structural diversity and application potential of hemicelluloses. 

Abatzoglou, N. and Chornet, E. (1998) Acid hydrolysis of hemicellulose and cellulose. Theory and Applications, in Polysaccharides, Marcel Dekkes, New York, pp. 1007-1045. 

The second area of application involves the use of cellulase-free xylanases for removal of hemicellulose from pulps (10-20) and plant fibres (21). It is essential that these xylanase preparations are free of contaminating cellulase activity or damage to the cellulose fibres and consequently the product quality will result. 

Figures 1 and 2 present some representative results for the application of Eq. 1 to describe data for hydrolysis of hemicellulose in corn stover in only water by batch and flowthrough systems, respectively. In Figs. 1 and 2, xylan conversion is calculated as the initial mass of xylan minus the mass of xylan at a time t all divided by the initial mass of xylan. Although the data are not presented, acid-catalyzed systems behaved similarly.

A branched pore leaching model as applied to release of water-soluble carbon from soil incorporates reaction to soluble compounds coupled with pore diffusion within the solids and leaching into the bulk solution. Application of such a model appears to describe hemicellulose hydrolysis reasonably well but not significantly better than chemical reaction only or simple leaching models. 

Wheat bran is mostly used today in feed, and rarely for nonfood applications. The quantity of bran produced in the European Union represents more than 7 million tons per year. Straw, another coproduct of wheat processing, also has strong potential tonnages [2] it contains a similar amount of hemicellulose as wheat... 

The most important application of cellulosic materials is the production of paper. Thus wood is transformed first into pulp by mechanical or chemical modification. Hardwood trees such as eucalyptus, birch, and softwood trees like pinus and spruce are used. In the Kraft process woodchips are treated with sodium hydroxide and sodium sulfide to promote the breakdown of the linkage between lignin, some hemicelluloses, and cellulose. This produces cellulose containing residual lignin. The latter is removed by a bleaching process that can apply several oxidizing agents. White pulp is pure cellulose that is used to produce paper. 

---