Date of Award

Fall 12-17-2021

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Food Science and Human Nutrition

Advisor

Jennifer Perry

Second Committee Member

L. Brian Perkins

Third Committee Member

Denise Skonberg

Abstract

Kombucha is a SCOBY-fermented tea beverage known for its taste, sensorial qualities, and high endogenous microbial load. In recent years, kombucha has become a popular functional food with a compound annual growth rate of 25% from 2015 to 2020 in American kombucha sales alone, and sales are predicted to keep increasing significantly over the next decade. However, kombucha is lacking in scientific research, and there is still much to be explored regarding its safety and native probiotic content. This research looked into the various routes of contamination of several kombucha systems as well as the feasibility of the producing a kombucha beverage with health-promoting characteristics derived from the inclusion of lactic probiotics.

Although bacterial spore contamination and survival in the kombucha SCOBY have been documented, it is unknown whether spores can survive in the liquid, or whether they can be transmitted to daughter SCOBYs. The foodborne pathogen and spore-former Bacillus cereus was inoculated into the SCOBY, unfermented liquid, and fermented liquid of three different kombucha systems. Data suggest that neither the route of contamination nor the kombucha system influenced the transmission or survival of B. cereus spores. The spread of the spores between culture and liquid across generation was shown to be sporadic but possible, so hygienic handling of kombucha cultures and raw materials throughout the entire production process is crucial to prevent uptake of pathogenic organisms. There was no survival of B. cereus spores after short-term storage or secondary fermentation, indicating that implementation of a holding step may mitigate potential food safety threats.

Kombucha is perceived to contain probiotics, but not all live cultures comprise probiotics. Some commercial kombucha products have validated probiotic strains added to them post-fermentation, but this can be costly. If probiotics, such as lactic acid bacteria, are inoculated into sweet tea prior to fermentation, they may be able to acidify the tea, replacing the need for utilizing previous kombucha or acetic acid, or survive and/or produce beneficial metabolites during fermentation in great enough amounts to convey a health benefit upon consumption. The survivability of six probiotic Lactobacillus sp. in acidified, sweetened tea at 25ºC during kombucha fermentation was established, and the medium (tea) and temperature (25ºC) were both revealed to affect the growth rates of the bacteria. Differences in pH indicated that the probiotics were unable to acidify the tea pre-fermentation. Although survival during fermentation was possible for four out of the six probiotics, it was concluded that probiotic Lactobacillus sp. are not well suited for a probiotic kombucha beverages, but out of the tested probiotics, Lactobacillus brevis and Lactobacillus fermentum were the most promising candidates.

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