Optimization of microbial consortia and materials composition enhances gluconic acid content in kombucha

The objective of this study was to optimize the microbial and ingredient composition of kombucha for enhanced production of gluconic acid (GA). Fourteen strains of Komagataeibacter spp. and one yeast strain of Dekkera sp. were isolated from kombucha. Among them, Komagataeibacter swingsii SS1 (SS1) and Komagataeibacter saccharivorans SS11 (SS11) were selected for their high GA production. A rapid reduction of pH, high GA content relative to acetic acid, and high cellulose production were observed in the tea infusion fermented by the microbial consortium (SS1 + SS11 + Dekkera bruxellensis Y24). From the correlation between the materials composition and quality indicators of kombucha, the decrease in pH was the most critical quality indicator of kombucha and the most closely related to GA content. Maximal GA production (11.7 mg/mL) was obtained under the conditions of 1% (w/v) tea extract, 8.5% (w/v) glucose, and 1.5% (v/v) ethanol through the optimization of materials composition by response surface methodology. The GA content of kombucha was enhanced threefold in comparison to general kombucha by fermentation with Komagataeibacter spp. and optimization of the composition of the ingredients. Overall, this study showed that a specific microbial consortium and materials composition could be established by correlation analysis among the ingredients, which results in increased GA levels in kombucha. These findings offer valuable foundational data for both commercial production and quality control of kombucha.