This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Narendranath, N. V. Articles by Power, R. Search for Related Content PubMed PubMed Citation Articles by Narendranath, N. V. Articles by Power, R. Agricola Articles by Narendranath, N. V. Articles by Power, R.

 Previous Article  |  Next Article 

Applied and Environmental Microbiology, May 2005, p. 2239-2243, Vol. 71, No. 5
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.5.2239-2243.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Relationship between pH and Medium Dissolved Solids in Terms of Growth and Metabolism of Lactobacilli and Saccharomyces cerevisiae during Ethanol Production

Alltech Biotechnology Center, Nicholasville, Kentucky 40356

Received 15 October 2004/ Accepted 24 November 2004

The specific growth rates of four species of lactobacilli decreased linearly with increases in the concentration of dissolved solids (sugars) in liquid growth medium. This was most likely due to the osmotic stress exerted by the sugars on the bacteria. The reduction in growth rates corresponded to decreased lactic acid production. Medium pH was another factor studied. As the medium pH decreased from 5.5 to 4.0, there was a reduction in the specific growth rate of lactobacilli and a corresponding decrease in the lactic acid produced. In contrast, medium pH did not have any significant effect on the specific growth rate of yeast at any particular concentration of dissolved solids in the medium. However, medium pH had a significant (P < 0.001) effect on ethanol production. A medium pH of 5.5 resulted in maximal ethanol production in all media with different concentrations of dissolved solids. When the data were analyzed as a 4 (pH levels) by 4 (concentrations of dissolved solids) factorial experiment, there was no synergistic effect (P > 0.2923) observed between pH of the medium and concentration of dissolved solids of the medium in reducing bacterial growth and metabolism. The data suggest that reduction of initial medium pH to 4.0 for the control of lactobacilli during ethanol production is not a good practice as there is a reduction (P < 0.001) in the ethanol produced by the yeast at pH 4.0. Setting the mash (medium) with 30% (wt/vol) dissolved solids at a pH of 5.0 to 5.5 will minimize the effects of bacterial contamination and maximize ethanol production by yeast.