Influence of microbial growth on the redox potential of fermented cucumbers

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 (E(h)) measurements, which are determined by the potential of an electron to reduce an acceptor, could serve as an alternative tool to monitor the progress of fermentation allowing the detection of the metabolic activity and/or growth of LAB and other microorganisms. Pasteurized and inoculated jars of cucumbers were observed to better understand how the E(h) 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 cucumbers including Lactobacillus plantarum, Zygosaccharomyces globiformis, and Enterobacter aerogenes. Although an initial decrease in E(h) was observed for all microorganisms, distinctive trends in E(h) occurred when these organisms were inoculated. After a 2-wk fermentation period, the E(h) (Ag/AgCl, 3 M KCl) in jars inoculated with L. plantarum, Z. globiformis, and E. aerogenes was at +453 +/- 55, +104 +/- 5, and -156 +/- 73 mV, respectively. Cucumbers inoculated with a mixture of L. plantarum and Z. globiformis had a terminal E(h) value of +202 +/- 24 mV, which was between that found for the individual microorganisms. L. plantarum dominated the E(h) trend when inoculated along with E. aerogenes with a final E(h) of +411 +/- 72 mV. The results showed that changes in E(h) continued after pH measurements became stable. Thus E(h) measurement can provide a tool to continuously monitor microbial growth during the course of cucumber fermentations.