Ethanol Production by Yeast Fermentation of Sweet Sorghum Juice

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Ahmed, Fatma Sir Elkhatim
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Ethanol is an organic compound produced by fermentation of sugars or starches ( after conversion to sugars) by yeast. This work was carried out to study the possibility of producing ethanol from sweet sorghum ( Sorghum bicolor (L) Moench) juice by fermentation using yeast (Saccharomyces cerevisiae) as an alternative or beside ethanol from molasses. In this study, three cultivars of sweet sorghum were used (95-24, 95-33 and local). They were grown at the Demonstration Farm, Faculty of Agriculture, University of Khartoum, Shambat, during the seasons of the years 2000 and 2001. The stem length and stem diameter for the plants were measured in the field. The crop was harvested at four stages of growth, starting 15 days after flowering: stage 1 cutting (S1) was 79 days after sowing, stage 2 cutting (S2) was 89 days after sowing , stage 3 cutting (S3) was 99 days after sowing and stage 4 cutting (S4) was 109 days after sowing. The juice was extracted immediately after harvesting and amount, pH, sugar content and type, nitrogen, protein, phosphorus ,magnesium, calcium, potassium and sodium were measured to determine the possibility of juice as a substrate for yeast growth and ethanol production. In this study the juice was inoculated with three yeast strains: commercial yeast DCL imported from United Kingdom, SAF imported from Turkey and strain 41 isolated at the Faculty of Agriculture, University of Khartoum. These study revealed that according to the amount of ethanol obtained ,the conditions of using crop season 2001 of cultivar (95-24), stage 3 (S3 , 99 days after sowing) using commercial yeast strain DCL gave the highest amount of ethanol, which amounted to approximately 837.0 liters per feddan. The biochemical changes during fermentation are characterized by the decrease in pH and sugars and the increase in ethanol production from the beginning of fermentation to 54 hrs then decreased. For the activity of yeast strain used in this study, ethanol yield increased when the juice was inoculated with young yeast inoculum , indicating that the activity of the inoculum decreased with time. In this experiment a techno-economic study to produce ethanol from sweet sorghum was carried out by calculating the cost of production which includes all agricultural operations harvesting , juice extraction, fermentation and distillation. the total revenue of production was calculated which equal to quantity of ethanol produced ( liters) x unit price + by – product ( forage) x price then the profitability was obtained which is equal to approximately 38.4%. The results revealed the potentiality of sweet sorghum as an energy crop and that it is economically feasible to produce ethanol from it
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Ethanol, Sweet Sorghum Juice, Yeast Fermentation