Microbial characterization of Kombucha during brewing and storage : a comparison of luxury Kombucha, home-brewed and commercialized

Sammanfattning

Kombucha is a fermented, slightly acidic drink that has been consumed since 220 BC. It has gained much popularity worldwide, in recent years, partially because of its benefitial microroganisms and its potential health benefits. Although the microbial community in Kombucha is diverse and varies between products, the main composition entails of acetic acid bacteria and yeasts, lactic acid bacteria. This study aims to characterize the composition of Kombucha; investigating Kombucha products from three different brands and using samples taken at different points of a homemade fermentation. With the variety of samples, an observation was done to understand if pasteurization and storage affect the microbial activity and composition. The main samples were taken from Källsjö Kombucha brewery, which requested to investigate three different vintages of two different Kombucha flavours; Sencha and Oolong. Comparatively, two commercialized Kombuchas, Humm and Renee Voltaire, were also studied. Furthermore, the brewery was also interested in analyzing the difference in the composition of one of their pasteurized bottles. The method used was isolating colonies for DNA amplification and sequencing to identify the yeasts and bacteria. For a better comprehension of the Kombucha composition, organic acids, ethanol, and glucose were measured with high-performance liquid chromatography (HPLC). The microbial activity in the different vintages of Sencha Kombucha, showed that the oldest vintage had the least microbial activity and diversity compared to younger products. Surprisingly, the Oolong vintage from 2022 showed the most microbial activity. Ethanol levels were lowest in the commercial Kombuchas. There was not much difference in the ethanol levels between pasteurized and unpasteurized. During the brewing process, the activity appeared to be the highest on days four and five, specifically in the selective media for yeast. It was apparent that there was little change in the glucose levels during the fermentation, whereas the acetic acid and ethanol increased with time. No lactic acid was found. In the Källsjö Kombucha, the dominant yeasts identified were Brettanomyces anomalous and Brettanomyces bruxellensis.