article · Biochemistry and Biophysics Reports
Yeasts vary significantly in their capacity to produce ethanol under different environmental conditions, driving the search for superior strains. Researchers isolated 211 yeast colonies from Ethiopian traditional fermented beverages, foods, soil, and fruits to evaluate their fermentation performance. Genetic and phenotypic profiling revealed that sixty percent of isolates produced ethanol, spanning four key genera. Several Saccharomyces cerevisiae strains and a Kluyveromyces marxianus strain produced between 7.6 and 9.0 grams per litre of ethanol from dextrose, matching or exceeding yields from standard commercial baker's yeast. Tested strains demonstrated tolerance to ten percent external ethanol, though tolerance declined at fifteen percent. Using response surface methodology, optimal fermentation parameters for pH, temperature, and incubation time were established for high-performing strains. The findings identify S. cerevisiae ETP53, K. marxianus ETP87, and Pichia fermentans ETP22 as effective candidates for ethanol generation.
Industrial ethanol production relies on robust microbial strains that can ferment sugars efficiently under diverse processing conditions. By screening wild yeast strains from indigenous fermented foods and natural environments, this research identifies resilient strains capable of matching commercial benchmarks. Discovering diverse, locally adapted microorganisms provides alternative biological resources that could improve the efficiency, stability, and temperature tolerance of industrial fermentation systems.
This research is at an early laboratory stage, focused on strain isolation, characterisation, and bench-scale process optimisation. The identified strains could eventually serve industrial ethanol distillers, biofuel processors, or beverage manufacturers seeking high-performing fermentative organisms. To move towards commercial use, these strains will require validation at pilot scale, testing on complex industrial feedstocks, and assessments of economic viability against incumbent commercial cultures.
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Yeasts are important microorganisms used for ethanol production; however, they are not equally efficient in the amount of ethanol production under different environmental conditions. It is, therefore, necessary to screen for elite strains to utilize them for commercial production of these commodities. In this study, yeasts were isolated from different Ethiopian traditional fermented alcoholic beverages (teji, tella, shamiata and areqe tinisis), milk and ergo, teff and maize dough, soil and compost, flowers, and fruits to evaluate their potential use for ethanol fermentation process. Isolates were screened for efficient ethanol production and the selected ones were identified using phenotypic and genetic characters using D1/D2 region of LSU rDNA sequence analysis. The yeast isolates were evaluated based on their growth and fermentation of different carbon sources. Response surface methodology (RSM) was applied to optimize temperature, pH and incubation time using central composite design (CCD) in Design-Expert 7.0.0. A total of 211 yeasts colonies were isolated of which 60% were ethanologenic yeasts (ethanol producers) and 40% were non-ethanol producers. The yeast population detected from various sources was in the range of 105 CFU from traditional foods and beverages to that of 103 CFU from fruits and soil samples. The data also showed that the number of colony types (diversity) did not correlate with population density. The highly fermentative isolates were taxonomically characterized into four genera, of which 65% of the isolates (ETP37, ETP50; ETP53, ETP89, ETP94) were categorized under Saccharomyces cerevisiae, and the remaining were Pichia fermentans ETP22, Kluyveromyces marxianus ETP87, and Candida humilis ETP122. The S. cerevisiae isolates produced ethanol (7.6-9.0 g/L) similar with K. marxianus ETP87 producing 7.97 g/L; comparable to the ethanol produced from commercial baker's yeast (8.43 g/L) from 20 g/L dextrose; whereas C. humilis ETP122 and P. fermentans ETP22 produced 5.37 g/L and 6.43 g/L ethanol, respectively. S. cerevisiae ETP53, K. marxianus ETP87, P. fermentans ETP22 and C. humilis ETP122 tolerated 10% extraneous ethanol but the percentage of ethanol tolerance considerably decreased upon 15%. S. cerevisiae ETP53 produced ethanol optimally at pH 5.0, 60 h, and 34oC. pH 4.8, temperature 36oC, and 65 h of time were optimal growth conditions of ethanol fermentation by K. marxianus ETP87. The ethanol fermentation conditions of P. fermentans ETP22 was similar to S. cerevisiae ETP53 though the ethanol titer of S. cerevisiae ETP53 was higher than P. fermentans ETP22. Therefore, S. cerevisiae ETP53, K. marxianus and P. fermentans ETP22 are good candidates for ethanol production.
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DOI: 10.1016/j.bbrep.2020.100886
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