Date of Award

Summer 8-23-2019

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Food Science and Human Nutrition

Advisor

L. Brian Perkins

Second Committee Member

Jennifer Perry

Third Committee Member

Mary Ellen Camire

Abstract

Kombucha is an effervescent fermented tea beverage that is gaining popularity for its probiotic nature and purported health benefits. The market for kombucha is expected to reach $1.8 billion by the year 2020. The composition of microbes that compose the symbiotic colony of bacteria and yeast (SCOBY) is highly variable with some species commonly found from the Gluconobacter, Acetobacter, Zygosaccharomyces, Saccharomyces, and Schizosaccharomyces genera.

It was hypothesized that different SCOBYs, obtained from different sources would vary in microbial diversity and produce different biochemical and flavor profiles in the resulting beverage over several generations. Kombucha is a fermented product and ethanol is often present in the final beverage, so it is important that a quality control method exist. The main objectives of this research were: (1a) to investigate the microbial variation between three SCOBYs of different origins and (1b) determine if there are significant differences within SCOBYs over 10 generations; (2) to determine the impact that the kombucha SCOBY has on the biochemical profile of the beverage; and (3) to learn the vocabulary words that consumers use to characterize the flavor notes in kombucha.

Kombucha was produced in a laboratory setting with three kombucha SCOBY pellicles prescreened for fermentate heterogeneity by High-performance liquid chromatography (HPLC) analysis. Two batches from each unique SCOBY were produced every 14 days. The liquid from batches 1, 5, 10, and the corresponding mother SCOBY were saved for downstream analysis including DNA sequencing with Oxford Nanopore’s MinION and HPLC analysis. A sensory evaluation study was also conducted to determine the vocabulary that consumers use to describe kombucha.

The two main microbes present in the SCOBYs tested in this research were Komagataeibacter xylinus and Gluconobacter oxydans. The diversity of the SCOBY did change slightly with time; however, over ten generations, the slight change in diversity was not significant (p-value > 0.05). By calculating beta diversity, Fisher’s alpha, Shannon diversity, and Simpson diversity, a clearer picture of the diversity of the SCOBY community between SCOBYs of different origins could be determined and demonstrated consortia to be quite different.

Investigating the two main microbes in kombucha, K. xylinus and G. oxydans, the Pearson correlations between the microbe and the flavor compounds acidic acid, lactic acid, glucose, fructose and sucrose were determined. K. xylinus was negatively correlated to glucose, fructose, lactic acid and acetic acid, and positively correlated to sucrose (part of the formulation) concentrations suggesting this microbe dominates earlier in the fermentation. G. oxydans was positively correlated to the concentrations of glucose, fructose, lactic acid and acetic acid, but negatively correlated to sucrose, suggesting it dominates later in the fermentation. However, these correlation coefficients were low and not significant.

A sensory evaluation study using 66 untrained panelists revealed the top 3 favorite flavors of kombucha amongst these panelists were ginger + other flavorings, ginger, and tropical flavors. Comparing two commercial and one lab-made kombucha sample showed that consumers found a significant difference in the vinegar, sour and bubbly flavor notes.

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