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Title: Homo- and heterofermentative lactobacilli differently affect sugarcane-based fuel ethanol fermentation

Author
item BASSO, THIAGO - Sao Paulo State University (UNESP)
item GOMES, FERNANDA - Sao Paulo State University (UNESP)
item LOPES, MARIO - Fermentec
item DE AMORIM, HENRIQUE - Fermentec
item Eggleston, Gillian
item BASSO, LUIZ - Sao Paulo State University (UNESP)

Submitted to: Antonie Van Leeuwenhoek
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/2013
Publication Date: 1/1/2014
Citation: Basso, T.O., Gomes, F.S., Lopes, M.L., De Amorim, H.V., Eggleston, G., Basso, L.C. 2014. Homo- and heterofermentative lactobacilli differently affect sugarcane-based fuel ethanol fermentation. Antonie Van Leeuwenhoek. 105:169-177.

Interpretive Summary: In fuel ethanol production the bacterial contamination of yeast fermentation broths still poses a great technological problem. Contamination by lactobacilli bacteria is largely dependent on the initial population of the bacteria and the yeast in the broths. Lactobacillus bacteria that depend on both glucose and fructose as their feedstock are the worst culprit for contamination as they are the most successful in competing with yeast for sugars during fermentation and cause the greatest loss in ethanol yields. These hetero-fermentative lactobacilli are prevalant in Brazilian fuel ethanol plants and are expected to be a problem in U.S. fuel ethanol plants.

Technical Abstract: The antagonism between by yeast and lactobacilli is largely dependent on the initial population of each organism. While homo-fermentative lactobacillus present higher inhibitory effect upon yeast when in equal cell number, in industrial fuel ethanol conditions where high yeast cell densities prevail hetero-fermentative lactobacillus are more deleterious, since they succeed in competing with yeast for sugars during fermentation. Both bacteria metabolic types caused reduced ethanol yield during yeast fermentation, but this effect was more pronounced with the hetero-fermentative strain in industrial fuel ethanol conditions. The greater glycerol formation by yeast as well as higher concentrations of bacterial metabolites produced (lactic and acetic acids, plus mannitol) and higher bacterial growth, all led to a greater sugar consumption and decreased ethanol yield in industrial yeast fermentation contaminated with the hetero-fermentative lactobacillus strain. Studies are in progress on the prevalence of homo- and hetero-fermentative lactobacilli in Brazilian fuel ethanol plants and on the differential effect of these two types of bacteria on glycerol production by yeast.