Bioethanol Production From High Sugary Corn Genotypes by Decreasing Enzyme Consumption

Introduction And Background

Currently the world is mostly dependent on fossil fuels to meet its energy demand, and more than 80% of the total global energy is obtained by burning fossil fuels (Escobar et al., 2009). However, rapid increase in the consumption rate of fossil fuels due to the growing industrialization and motorization of the world has resulted in the fast depletion of these limited and non-renewable energy sources. The usage of fossil fuels has also raised another concern for its contribution to the emission of greenhouse gases and global warming that causes climate change, rise in sea level, loss of biodiversity and urban pollution (Farrell et al., 2006). Therefore, it is necessary to find out an alternative energy source by using renewable, sustainable, efficient and cost-effective raw materials with lower emissions of greenhouse gases. In this regard, biofuels are considered promising alternatives to fossil fuels that include bioethanol, bio-butanol, vegetable oils, biodiesel, biogas, bio-oil, bio-char, Fischer-Tropsch liquids, and bio-hydrogen.

Among the biofuels, bioethanol is the most attractive for its ease of production and lack of toxicity. Many countries such as USA, Brazil, China, and several EU member states have already proclaimed commitments to bioethanol programs as a renewable energy source. As a whole, bioethanol provides multiple economic, social and environmental benefits to the regions and countries that produce it. Domestic production and use of bioethanol can obviously reduce the dependence on foreign oil and trade deficits, create jobs in rural areas, and decrease air pollution, climate change and CO₂ build up (Ibeto et al., 2011). Burning of ethanol rather than gasoline can decrease carbon emissions by more than 80%, and eliminate entirely the release of sulphur dioxide that causes acid rain (Lashinky & Schwartz, 2006; Mussatto et al., 2010). In addition, bioethanol can be used as a replacement of the methyl tertiary butyl ether (MTBE), which is used as an octane enhancer for gasoline but contaminates the ground water used for drinking purpose (Green & Lowenbach, 2001; McCarthy & Tiemann, 1998).

Bioethanol can be produced from a variety of renewable sources, which are broadly classified into sugars, starch and cellulosic biomass. In general, carbohydrate rich plant biomasses are widely used for ethanol production that include corn, wheat, cassava, sugarcane, sugar beet, sweet sorghum, barley, potatoes, bagasse, straws, wood, paper, grasses and agricultural residues (Ibeto et al., 2011). Among them, sugarcane is a major raw material used in the tropical countries like Brazil and India (Quintero et al., 2008), while starchy biomass is used in North America and

Europe (Balat & Balat, 2009; Sanchez & Cardona, 2008; Yangcheng et al., 2013). In recent years, extensive research efforts have been made on the conversion of lignocellulosic biomass into ethanol as attempts to meet the growing demand for ethanol and reduce the use of food crops. However, production of ethanol from lignocellulosic biomass is more difficult, complicated and costly when compared to sugar and starch-based ethanol production. For this reason, almost all the current commercial ethanol is produced from sugar and starch, where the latter is relatively well established and spreaded globally than sugar-based ethanol production facility (Quintero et al., 2008). Among the starch based raw materials, corn is dominantly used for bioethanol production and its use has been increased dramatically during the last two decades, particularly in the USA, Canada, China and some European countries (Balat & Balat, 2009; Johnston & McAloon, 2014).