The effect of the fermented tea beverage kombucha on the gut microflora

English. Introduction The fermented tea drink kombucha has gained large popularity over the past years. It has been praised for its nutritional content, organic acids and living community of beneficial bacteria. Multiple studies have been conducted on the effect of the nutrients and organic compounds on the body, but none on the effect of the microbial community on the human gut microbiota. That is thus the aim of this study. Materials and methods The study consisted of two parts. Firstly, the microbial community of kombucha was studied by culturing on an array of different media, with different pH and conditions. Colonies were then counted and large ones were randomly selected for sequencing. The second part of the study consisted of a human trial, in which 42 participants consumed either living kombucha, sterilized kombucha of water during a period of three weeks. Fecal samples were collected after a washout period, prior to the trial, at the end of the three weeks and another ten days later. DNA from the samples was extracted, amplified and sequenced using Illumina sequencing. Results The kombucha used for the study was seemingly dominated by yeast, and contained 104-105 CFU/ml. No lactic acid bacteria or Enterobacteriaceae could be cultured. The data collected from the human study did not show an effect of treatment with living or sterilized kombucha. The results did show the composition of the microbial communities of the gut, even though they did not change significantly. Discussion The kombucha shows a low microbial content, below what is recommended as a probiotics dose. Yet the microbes present were hard to culture, and in many cases formed to small colonies to count. This implies that either the concentration is low, or that the result does not reflect the true microbial content due to a large part of the microbes being non-culturable, which has been the case in previous studies. The data obtained from the human study seems sensitive and reliable enough to be able to draw conclusions from. There seem to have been some errors in the handling of the samples, although these are not believed to have affected the results. Conclusion The study found no effect of kombucha on the intestinal flora after three weeks of consumption. In order to improve the analysis of the kombucha itself, molecular methods should be used to analyze the community properly, and culturing conditions optimized to be able to get a better picture of the amount of living microbes.

English. The fermented tea drink kombucha has become an increasingly trendy drink during the past couple of years. Although it has historically been known for its health benefits in Asia, it has taken until recently for it to gain popularity in Western countries. Riding on the current health wave in society, kombucha is surrounded by numerous health claims, such as a high content of nutrients and beneficial fermentation products as well as being probiotic if consumed raw. Still little research has been done on the subject, meaning that few of these claims may be scientifically proven. Tightening regulations have made it harder for food producers to place health claims on their product, including claims of probiotic effects. In order for a product to be classified as probiotic, it must contain a large amount of living bacteria that survive the digestive system and reach the colon. Even though some positive health effects can come from consumption of dead bacteria, living bacteria can in some cases colonize the colon or temporarily change the gut flora to the better. Probiotics have positive effects on the gut as well as the immune system, and has recently become a hot research topic as more and more interesting connections are found. Proving a probiotic effect of a food product is thus of high relevance for the producer. This study investigated if the consumption of kombucha has an effect on the gut microbiota, and further if it depends on the content of living bacteria or is inherent even to a sterilized version of the drink. The study consisted of two parts. Firstly, the present species of bacteria and yeast in the kombucha culture were studied, as well as which are dominant and the content of living bacteria. Secondly a human study was performed to investigate the effect on the gut microflora. 42 participants were divided into three groups of which one consumed live kombucha; one sterilized kombucha with no living microorganisms; and one sterile water. The study took place over a period of three weeks. Fecal samples were taken before the start of consumption, the day after ended consumption and ten days after the ended consumption. After studying the microbial communities of the fecal samples from the different groups, no significant effect of the kombucha could be found. There was no change in the composition of the gut flora for the group consuming either live or sterilized kombucha. It was also found that the kombucha used for the study was dominated by yeast, which has not been studied for its probiotic potential to the same extent that bacteria have. It also did not contain as many living microorganisms as are recommended as a probiotic dose. A deeper analysis of the microbial community of the kombucha might give a better picture of it, and reveal a larger part of living bacteria. Many of the microbes that were found in the kombucha were hard to study in a laboratory environment, meaning the community may actually be different than what this study found. Previous studies have been able to identify a much larger number of bacteria. This may also increase the total number of microbes in the kombucha, although the results found in the study are consistent with the literature. The data from the human trial was seemingly reliable as it showed clear correlations between the communities from one participant at different times, which was to be expected. The gut microbial community is relatively constant. This proves that the methods used were sensitive enough to provide good results. Also, there was a clear differentiation between the actual samples and the negative control samples, which were used to verify the procedures. All in all, the methods for sample handling and data treatment seem to have been reliable enough to present the clear conclusion that there was no effect of treatment. There is more work to be done in studying the community of kombucha as well as the drink’s different health benefits. Despite the many, often positive, effects kombucha may have on the body; this study shows that altering the gut flora is not one of them. Nevertheless, it is a beverage that is enjoyed by many and many of the participants of the study experienced positive changes from drinking it such as decreased flatulence and improved stools. The many other health benefits of kombucha remain.