Characterization of Wild Yeasts Isolated From Fermented Sweet Sorghum (Sorghum Bicolor L.) Juice and their Potential for Bioethanol Production
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Date
2019-02-03
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Addis Ababa University
Abstract
Nonrenewable energies have been used as the major sources of energy in the world so far. However, they are not sustainable and environmentally friendly. Sweet sorghum is found to be important source of energy that is renewable and less contribute to global warming. The objective of this study was to produce bioethanol through fermentation of sweet sorghum juice by yeast isolated from fermented sweet sorghum juice (SSJ) samples. Two varieties of sweet sorghum were compared for ethanol production at optimized fermentation conditions. Compared to variety 1, higher ethanol content was obtained from variety 2. The yeasts isolated from fermenting sweet sorghum juice were characterized using various tests. About 18 yeast isolates were selected from total of 50 isolates based on sugar fermentation test. Phenol sulfuric acid method and refractometer were used to determine the sugar content of the sweet sorghum juice. The estimated reducing sugar was determined using 3, 5-dinitrosalysalic acid method. The estimated carbohydrate concentration of the mixture juice from the two varieties was 37.402 g/L to 157.641 g/L. The estimated reducing sugar content was found varying from 4.644 g/L to 33.412 g/L. Optimization process was carried out at different temperature, pH and incubation period using completely randomized factorial design. Ethanol content was determined using potassium dichromate solution. The most ethanol tolerant yeast isolates of SJU13 and SJU14 were used for fermentation of SSJ. Maximum 18.765% (v/v) ethanol was produced at pH 4.5 and 30/26 oC for 96 hours using co-culture of SJU13 and SJU14 potent yeast isolates isolated from fermenting sweet sorghum juice. The selected indigenous yeast was more adaptive to its substrate and was found fermenting the sugar and gave a higher ethanol yield compared to commercial S.cerevisiae. There was highly significant difference between the mean oBrix of variety 1 and variety 2 of sweet sorghum stalk. Further study is recommended in order to examine different cultivars of sweet sorghum from all regions of Ethiopia and identify the best variety for the source of ethanol production.
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Sugar, Fermentation, Brix, Variety and Optimization, Indigenous Yeasts