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Abstract
Kombucha is a traditional low-alcoholic beverage made from sugared tea and transformed by a complex microbial consortium including yeasts and acetic acid bacteria (AAB). To study the microbial interactions and their impact on the chemical composition of the beverage, an experimental design with nine couples associating one yeast strain and one AAB strain isolated from original black tea kombucha was set up. Three yeast strains belonging to the genera Brettanomyces, Hanseniaspora, and Saccharomyces and three strains of Acetobacter and Komagataeibacter species were chosen. Monocultures in sugared tea were analyzed to determine their individual microbial behaviors. Then, cultivation of the original kombucha consortium and cocultures in sugared tea were compared to determine the interactive microbial effects during successive phases in open and closed incubation conditions. The results highlight the main impact of yeast metabolism on the product’s chemical composition and the secondary impact of bacterial species on the composition in organic acids. The uncovered microbial interactions can be explained by different strategies for the utilization of sucrose. Yeasts and AAB unable to perform efficient sucrose hydrolysis rely on yeasts with high invertase activity to access released monosaccharides. Moreover, the presence of AAB rerouted the metabolism of Saccharomyces cerevisiae towards higher invertase and fermentative activities.
Highlights
Fermented food is often designated as a convenient model for the study of microbial communities and interactions [1,2,3]
The comparison of parameter plots of P1 and P2 reflects the shift from the combined yeasts and acetic acid bacteria (AAB) metabolisms, with a positive correlation of invertase activity, fermentation, and acidification during the acidification phase (Figure 8a), towards the prevalence of yeast metabolism, with a lower correlation with AAB oxidative metabolism during the carbonation phase. These results show that yeast metabolism was key throughout the process of fermentation: P1 required yeasts to hydrolyze sucrose and produce ethanol for their conversion into acetic and gluconic acids by AAB and P2 relied on fermentation to complete natural carbonation
Microbial interactions occurring in kombucha have often been described as “symbiotic”, which does not imply mutual benefits, as described by the word “mutualistic”, but rather that all species manage a stable coexistence, possibly through interactions that are yet to be defined [1,13]
Summary
Fermented food is often designated as a convenient model for the study of microbial communities and interactions [1,2,3]. Kombucha is an increasingly exploited example of a fermented beverage obtained by microbial communities. Named “kombucha tea”, results from the metabolic interplay of a microbial consortium including acetic acid bacteria (AAB), yeasts, and often (but not always) lactic acid bacteria in sugared tea liquor [4,5,6]. Infusion provides nitrogenous substances extracted from tea necessary for the growth of microorganisms. Sucrose is converted into glucose and fructose by periplasmic yeast invertase and ethanol is produced as a result of alcoholic fermentation. AAB oxidize glucose into gluconic acid and ethanol into acetic acid through oxidative metabolism
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