Microbial metabolic transformation and antioxidant activity evaluation of polyphenols in kombucha

Kombucha is a kind of traditional fermented sugared tea rich in polyphenols. Although the health effects of tea polyphenols (TPPs) have been extensively studied, the biotransformation of the TPPs during kombucha fermentation was not fully elucidated. In this study, the polyphenol transformation capacity of microbial strains and the synthetic microbial communities during the tea broth fermentation were investigated. Firstly, six mi-crobial species demonstrated different polyphenol transformation abilities: Acetobacter pasteurianus, Zygo-saccharomyces bailii and Debaryomyce hansenii could increase the contents of epigallocatechin gallate (EGCG), the most abundant components of TPPs. Z. bailii and Acetobacter xylinum could enhance the concentration of TPPs with low molecular weight. Then, four synthetic microbial communities (SMC) consisting of different species were constructed to ferment the black tea broth. When different strains coexisted, their interaction could further enhance kombucha's phenols transformation and antioxidant activity. Specifically, the SMC, constructed by Z. bailii, L. plantarum and D. hansenii, could enhance the EGCG content significantly in tea broth and the total phenols and flavonoid contents. Meanwhile, the antioxidant activities of kombucha fermented by this SMC were found to be relatively high among different fermented tea broth groups. Besides, it is demonstrated that A. pasteurianus was a strong competitor in the tea broth environment. This bacterium could decrease the number of viable yeast cells by producing more acid. This study demonstrated that the construction of suitable synthetic microbial communities would help reveal the phenolic metabolic characteristics of complex microbial com-munities and obtain customizable phenolic combinations for kombucha products.