Comparative Study on Batch Ethanol Fermentation Performance of Saccharomyces cerevisiae and Zymomonas mobilis in Equimolar Mixture of Glucose and Fructose Substrates

Author : Arga Jr., Richard Caraig
Major Adviser : Bataller, Butch G.
Major Co-Adviser : Nayve, Jr., Fidel Rey P.; 
Committee Members : Gatdula, Kristel M.; Alcantara, Jerico Z.
Year : 2020
Month : July
Type : Thesis
Degree: BS
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Keywords: bioethanol, glucose-fructose, mixed sugar, Saccharomyces cerevisiae, yeast, Zymomonas mobilis
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Two of the most known ethanol producers are S. cerevisiae and Z. mobilis which perform well under pure hexose media. However, when mixtures of glucose and fructose are used, S. cerevisiae exhibits glucose preference over fructose which leads to stuck fermentation while Z. mobilis converts some amount of fructose to sorbitol, both leading to lower ethanol production efficiency. In the Philippines, high fructose corn syrup (50% glucose and 50% fructose) is in excess supply making it a viable substrate. To determine the better microorganism that could maximize ethanol production upon fermenting equimolar mixture of glucose and fructose like HFCS, various literatures were collected online and different fermentation parameters and characteristics were evaluated. After comparison, hierarchy of prioritization were suggested that serve as a selection criteria for industrialization of the process. It was found that S. cerevisiae has wider temperature (1-45o C) and pH (2.5-8.0) tolerance, lesser susceptibility to infection, higher ethanol yield (0.454 to 0.507 g/g), and lesser by-products formation. It has dominated the top 5 priorities of the suggested criteria. Meanwhile,Z. mobilis has lower biomass yield (0.010 to 0.030 g/g), higher ethanol-to-biomass ratio (13.98 to 42.60 g/g), cheaper nitrogen requirement (N2 gas), and greater amenability to genetic improvement. Both have the same ethanol tolerance (126 g/L). From the results, it was concluded that S. cerevisiae is the better organism in terms of performance because of its resilient nature, high ethanol production, and easier disinfection. However, in terms of profitability, an economic analysis is still needed because it is disadvantaged by Z. mobilis at biomass production and media needs. The comparative study could be improved by studying the optimized conditions and evaluating its financial aspect.

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