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KMID : 0545119950050060309
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Journal of Microbiology and Biotechnology
1995 Volume.5 No. 6 p.309 ~ p.314
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Bacterial Contamination and Its Effects on Ethanol Fermentation
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Chang, In Seop
Kim, Byung Hong/Shin, Pyong Kyun/Lee, Wan Kyu
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Abstract
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Samples were collected from a commercial ethanol production plant to enumerate the bacterial contamination in each step of a starch based ethanol production process. Though the slurry of raw material used in the process carried bacteria with various colony morphology in the order of 10^4 per ㎖, only the colonies of white and circular form survived and propagated through the processes to the order of 10^8 per ㎖ at the end of fermentation. Almost all of the bacterial isolates from the fermentation broth were lactic acid bacteria. Heterofermentative Lactobacillus fermentum and L. salivarius, and a facultatively heterofermentative L. casei were major bacteria of an ethanol fermentation. In a batch fermentation L. fermentum was more detrimental than L. casei to ethanol fermentation. In a cell-recycled fermentation, ethanol productivity of 5.72 g l^-1 h^-1 was obtained when the culture was contaminated by L. fermentum, whilst that of the pure culture was 9.00 g l^-1 h^-1. Similar effects were observed in a cell-recycled ethanol fermentation inoculated by fermentation broth collected from an industrial plant, which showed a bacterial contamination at the level of 10^8 cells per ㎖.
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