Influence of microbial growth in the redox potential of fermented cucumbers

Authors: OLSEN, MEAGAN - 6645-10-00 - TEMP; Perez Diaz, Ilenys

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/2/2009
Publication Date: 5/1/2009
Citation: Olsen, M., Perez Diaz, I.M. 2009. Influence of microbial growth in the redox potential of fermented cucumbers. Journal of Food Science. 74(4):M149-M153.

Interpretive Summary: Measurements of the hydrogen ions concentration (pH) on fermented cucumbers are commonly used to indirectly monitor the progress of acid production. However, measurements of the flow of electrons (Eh) in cucumber tanks as opposed to the hydrogen ions could serve as a more accurate tool to monitor the progression of the fermentation in the field. Furthermore, measurements of the flow of electron could aid in the early detection of undesired yeast growth. Cultures of a bacterium responsible for acid production and fermented cucumber spoilage yeasts were added to pasteurized cucumber jars and changes in Eh were observed. Although an initial decrease in Eh was recorded for all jars, distinctive trends in Eh depended on the added microbe. Different trends were observed when the acid producer and the yeast cultures were added. The results indicate that changes in Eh continue to be detectable two days after pH measurements became stable. Thus determination of Eh may serve as a more accurate tool than pH in monitoring microbial growth and detecting undesired yeast growth in field cucumber fermentations.

Technical Abstract: Commonly, pH measurements are used during the production of fermented cucumbers to indirectly monitor growth of lactic acid bacteria (LAB) and acid production. Redox potential (Eh) measurements, which are determined by the flux of electrons in a system, could serve as a more accurate tool to monitor the progression of the fermentation in the field allowing the detection of the metabolic activity and/or growth of LAB and other microbes such as yeasts. Pasteurized and inoculated cucumber jars were observed to better understand how the Eh changes during the cucumber fermentation and how it could be used as a monitoring tool. Jars of diced, brined cucumbers were pasteurized and inoculated with microbes previously isolated from fermented cucumber tanks such as Lactobacillus plantarum, Zygosaccharomyces globiformis, and Enterobacter aerogenes, or a dual combination of them. Although an initial decrease in Eh was recorded for all jars, distinctive trends in Eh depended on inocula types. Over the 2 weeks fermentation the Eh on jars inoculated with L. plantarum, Z. globiformis and E. aerogenes increased to +738 ± 123 mV, was maintained at -452 ± 25 mV and decreased to -1812 ± 429 mV, respectively. Jars inoculated with L. plantarum and Z. globiformis had a terminal Eh value of -14 ± 104 mV, falling in between the individual measurements for jars containing each organism individually. L. plantarum dominated the Eh trend when inoculated along with E. aerogenes generating a final Eh of +486 ± 72 mV. The results indicate that changes in Eh continue to be detectable two days after pH measurements became stable. Thus determination of Eh may serve as a more accurate tool than pH in monitoring microbial growth and detecting undesired yeast growth in field cucumber fermentations.