Abstract
The current trend in volatile oil prices, global warming and environmental pollution, has encouraged major consumers worldwide to sharply increase their use of “green” fuels. Bioethanol is usually obtained from the conversion of carbon-based feedstock. Bioethanol from biomass sources is the principal fuel used as a fossil fuels’ substitute for road transport vehicles. Bioethanol is predominantly produced by the sugar fermentation process, although it can also be generated by the chemical process of reacting ethylene with steam. Finger millet (Eleusine coracana) is also known as Ragi (India), Kodo (Nepal), Uburo (Rwanda), Kurakkan (Srilanka), Bulo (Uganda), Kambale (Zambia) and Tamba (Nigeria) and can be used as an efficient source for bioethanol production. Despite all its importance, however, finger millet is still grossly undervalued both scientifically and internationally. This review observes current progress in bioethanol production from E. coracana feedstock and the effectiveness of various technological approaches for that. The main aspects of ethanol production from finger millet seeds have been considered. Seeds, which are already used for brewing, are the most obvious variant of feedstock for ethanol production from this crop. The conversion of finger millet straw and agricultural waste into bioethanol has also been reviewed. Practical results of development and testing the tentative technology of sweet sorghum and finger millet combined processing into bioethanol are described. The concept of the tentative technology of bioethanol production from carbohydrate raw material of the first and second generations is suggested.
Highlights
Greenhouse gases (GHG) emissions and fossil fuel depletion are currently viewed as the major challenges of global industrial development [1, 2]
Urea and yeast extract produced higher, but still rather low alcohol output – 11% v/v, while mash with yeast extract and mineral additives allowed to obtain 15.6% v/v ethanol in the final product. These results suggest that the very high gravity (VHG) fermentation technology could solely be based on finger millet’s reducing sugars medium [96], contrary to a study [95], where E. coracana was only a source of flour as an additive to free-sugars based medium
Cultivation of finger millet on fully supplemented soil resulted in almost 50% increase of production [83]. These results revealed an extra potential for elevating the bioethanol production efficiency from finger millet
Summary
Greenhouse gases (GHG) emissions and fossil fuel depletion are currently viewed as the major challenges of global industrial development [1, 2]. Since biomass and plant waste are mainly used as feedstock for second-generation bioethanol production, large amounts of sugars are not available for fermentation because these are polysaccharides - cellulose and hemicellulose. As the search for new high-efficient feedstock is in progress, minor grains and cereals, called orphan crops, which are grown locally in some regions or have been neglected, are drawing a renewed interest [24] One of such plant groups is represented by small millets that include finger millet (Eleusine coracana), foxtail millet (Setaria italica), kodo millet (Paspalum scrobiculatum), proso millet (Panicum miliaceum), barnyard millet (Echinochloa spp.) and little millet (Panicum sumatrense). The effectiveness of various technological approaches for such production and future prospects for finger millet usage for these purposes are reviewed
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