Across the globe, there is a rising need to find out new and cheap carbohydrate sources for bioethanol produc­tion (Mohanty et al., 2009). Presently, a serious focus is on biofuels made from renewable energy crops such as sugarcane, corn, wheat, soybeans, etc. In a given produc­tion line, the comparison of the biomass includes several issues: (1) cultivation practices, (2) chemical composi­tion of the biomass, (3) use of resources, (4) emission of GHGs, (5) availability of land and land use practices, (6) soil erosion, (7) energy balance, (8) price of the

biomass, (9) contribution to biodiversity and landscape value losses, (10) direct economic value of the feedstock, (11) water requirements and water availability, (12) cre­ation or maintain of employment, and (13) logistic cost (transport and storage of the biomass) (Gnansounou et al., 2005).

Bioethanol feedstock can be divided into three major groups: (1) sugar-based feedstock (e. g. sugarcane, beet sugar, sorghum and fruits), (2) starchy feedstock (e. g. corn, sweet potato, rice, potatoes, cassava, wheat and barley), and (3) lignocellulosic feedstock (e. g. wood, straw, grasses, and corncob). In short term, production of bioethanol as a fuel is almost entirely dependent on starch and sugars from existing food crops (Smith, 2008; Potumarthi et al., 2012). The negative part in pro­ducing bioethanol from starch and sugar is that the feed­stock tends to be costly and demanded by other applications as well (Enguidanos et al., 2002). Lignocel — lulosic biomass is envisaged to provide a major portion of the raw materials for bioethanol production in the long term due to its low cost and high availability (Gnansounou et al., 2005).

Up to 2003, about 60% of global bioethanol was ob­tained from sugarcane and 40% from all other crops (Dufey, 2006). Brazil utilizes sugarcane for bioethanol production, while the United States and other western countries mainly use starch from corn, wheat and barley (Linde et al., 2008). Brazil is the largest producer of sug­arcane with about 672,157,000 tons of global production followed by India, second largest producer with

285,029,0 ton production (Food & Agricultural Orga­nization of United Nations, 2013).

Bioethanol production in Brazil is less expensive than in the United States from corn or in Europe from sugar beet, because of lower labor costs, shorter processing
time, lower transport costs, and other input costs. After sugarcane, starch is the high-yield feedstock for bio­ethanol production, but pretreatment is necessary to produce bioethanol by fermentation (Pongsawatmanit et al., 2007). Starch is a homopolymer consisting mono­mers of D-glucose and for bioethanol production it is necessary to break down this carbohydrate for obtaining glucose syrup, which can be further transformed into bioethanol by yeasts. Starch-based feedstock are the most utilized for bioethanol production in America and Europe.

Biomass from agricultural waste (wheat straw, sugar­cane bagasse, etc.), wood, and energy crops are attrac­tive materials for bioethanol production since it is the most abundant reproducible assets on earth (Figure 1.3). The existing biomass from crops could produce up to 442 American billion liters per year of bioethanol (Bohlmann, 2006). Thus, the total possible bioethanol production from crop residues and wasted crops is 491 American billion liters per year, about 16 times higher than the existing world bioethanol production. Advantages of biofuels are as follows: (1) biofuels are easily available from common biomass sources, (2) bio­fuels have a considerable environmentally friendly po­tential, and (3) they are biodegradable and contribute to sustainability (Balat, 2007; Mekala et al., 2008). Although lignocellulosic biomass is the best alternative source, initial pretreatment is a must to attain simple sugars for simultaneous ethanol fermentation.