![]() ![]() It is also well known that hydrolysis of hemicelluloses produces / liberates organic acids that could inhibit fermentation of the carbohydrate.Ĭellulosics being an alternative for ethanol production, there is still an important aspect that has to be considered: the cost of the feedstock. Studies have shown that fermentation of all the glucidic part of the hemicelluloses, both C6 and C5 sugars, was feasible using nontraditional microorganisms ( Agbogbo & Coward-Kelly, 2008 Casey et al., 2009 Chu & Lee, 2007 Upon hydrolysis, the C6 fraction of these carbohydrates can effectively be converted to ethanol via fermentation using classical yeast strands ( Gírio, 2009). Hemicelluloses are, as cellulose, macromolecules composed of carbohydrates. Lignin, has low oxygen content and thus a high energetic value. ![]() Lignin is a macromolecule composed of phenylpropane units bond together via, predominantly, ether bonds although C-C between moieties are also significant. The other macromolecules found in the lignocellulosic matrix are also of interest. Whilst the crystalline form is difficult to disassemble with hydrolyzing agents, the amorphous phase has a certain level of disorder that makes relatively easy the penetration and action of hydrolysing agents, either enzymes or ionic species. A typical fibril will have zones that are crystalline separated by zones that are amorphous. The natural macromolecule is usually present in nature in two forms: crystalline and amorphous. The polar hydroxyl groups are oriented one toward the other so that interaction with a polar medium (as a solvent) is fairly difficult making cellulose water resistant. The cellulose macromolecule is composed of glucose units linked together via β-1,4-glycosidic bonds (or acetal bonds) creating long chains that combine together to form fibrils and eventually fibres. Cellulose, the most abundant carbohydrate on the planet, is a fraction of the complex lignocellulosic matrix along with other macromolecules, lignin, hemicelluloses, and extractives. Lignocellulosic biomass, either from forestry or agriculture offers such potential. Increased use of biofuels requires alternative sources of biomass that lower water and energy consumption and do not compete with food supplies. First generation biofuels have had a bad press: high water and energy consumption (very significant is the energy used in the production of the fertilizers needed by agriculture) and the fuel versus food controversy. The first generation of biofuels, made out of starch (ethanol) or triacyglycerol (biodiesel) uses expensive homogeneous feedstocks (sugar cane, corn, wheat and edible oils) coupled with relatively inexpensive technologies known and practiced for years at an industrial level. ![]()
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