Viability and Diversity of the Microbial Cultures Available in Retail Kombucha Beverages in the USA

Kombucha is a two-stage fermented sweetened-tea beverage that uses yeast and lactic acid bacteria (LAB) to convert sugars into ethanol and lactate, and acetic acid bacteria (AAB) to oxidize ethanol to acetate. Its popularity as a beverage grew from claims of health-benefits derived from this vibrant microbial bioconversion. While recent studies have shed light on the diversity of cultures during a Kombucha fermentation, there is limited information on the diversity, and especially viability, of cultures in retail beverages that advertise the presence of Kombucha and probiotic cultures. In this study, 12 Kombucha beverages produced by different manufacturers throughout the US were purchased and microbially characterized. Eight of the beverages contained viable Kombucha cultures, while 3 of the remaining 4 had viable Bacillus cultures as added probiotics. Amplicon profiling revealed all contained Kombucha yeast and bacteria cells. The dominant yeast detected were Lachancea cidri (10/12), Brettanomyces (9/12), Malassezia (6/12) and Saccharomyces (5/12). Dominant LAB included Liquorilactobacillus and Oenococcus oeni, and AAB were Komagataeibacter, Gluconobacter and Acetobacter. One beverage had a significant amount of Zymomonas mobilis, an ethanol producing bacterium from Agave cactus. While Kombucha beverages differ in the types and viability of cultures, all except one beverage contained detectable viable cells.