Determining the redox potential of a system can be a useful tool in evaluating the thermodynamic changes that occur over a period of time. Currently, fermentation industries use pH measurements to assess the progress of fermentation and growth of lactic acid bacteria (LAB). Redox potential (Eh) measures the transfer of electrons within a system, rather than solely the concentration of hydrogen ions, as measured by pH. Continuous monitoring of fermentation by Eh may allow for more descriptive analysis of the metabolic process and could offer a method for the earlier prediction of spoilage by yeasts. The trends in redox potential of fermenting cucumbers were observed to evaluate the possible application of this parameter in monitoring the development of fermentation. Additionally, an evaluation of the effect of gas purging on microbial growth during the fermentation was conducted using redox potential trends as a monitoring tool. Cucumbers were packed and brined using sodium chloride, calcium chloride, and acetic acid and the redox potential monitored during fermentation. Examination of both pasteurized-inoculated jars and non-pasteurized jars was conducted in this study. In addition, changes in redox potential were measured in fermentations that were purged with nitrogen, oxygen, hydrogen, or left untreated. Brine samples were analyzed for microbial counts, pH and substrates and products of fermentation. Under conditions representative of a standard cucumber fermentation, a dramatic decrease in the redox potential was observed during the first day, concomitantly with the initiation of the log phase of bacterial growth. However, in the presence of spoilage yeast, redox potential remained low over this initial period. The progress of a fermentation sparged with nitrogen, oxygen, or no treatment produced similar Eh trends. The Eh trend was more reduced under hydrogen sparging. A heightened growth rate for LAB, more efficient production of lactic acid, and lower production of ethanol occurred with nitrogen sparging. The evidence suggests that the growth of yeasts in a cucumber fermentation could be detected based upon differences in the redox potential. Distinct variations in Eh were still recorded after pH values decreased and remained constant, suggesting the valuable possible application of Eh to monitor industrial cucumber fermentations. Additionally, changes in redox potential were affected by gases introduced during cucumber fermentations and sparging with nitrogen could have substantial benefits to the industry.
| Identifer | oai:union.ndltd.org:NCSU/oai:NCSU:etd-11052008-141935 |
| Date | 05 December 2008 |
| Creators | Olsen, Maegan Jessie |
| Contributors | Ilenys M. Pérez-DÃaz, Roger McFeeters, Todd Klaenhammer |
| Publisher | NCSU |
| Source Sets | North Carolina State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://www.lib.ncsu.edu/theses/available/etd-11052008-141935/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dis sertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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