Abstract
Kombucha is a traditional beverage obtained from the fermentation of sugared tea by a symbiotic culture of bacteria and yeast (SCOBY), whose metabolism contributes significantly to the phytochemical composition and health-promoting properties of the final product. Among the phenolics present, gallic acid stands out as a multifunctional molecule with antioxidant, anti-inflammatory, and cardio-protective activities, making it a compound of growing interest for the development of functional foods, nutraceuticals and cosmetics. While gallic acid in kombucha has typically been attributed to plant-derived precursors, its potential de novo microbial origin has remained largely unexplored. In this work, robust evidence supports that SCOBY can synthesise gallic acid directly from sugars, without the contribution of tea or other plant materials. Metabolomic analyses combined with physicochemical characterisation (pH, ethanol, acetic acid, total soluble solids, sucrose, glucose, and fructose) revealed a linear increase in gallic acid production under standard fermentation conditions, associated with the microbial community's tolerance to high sugar concentrations and its metabolic capacity to generate bioactive phenolics. This finding highlights a previously unrecognised role of SCOBY as a natural cell factory for gallic acid production. In contrast to metabolic engineering approaches in model microorganisms such as Escherichia coli or Pseudomonas, our study demonstrates that a non-engineered microbial consortium can achieve this transformation simply and sustainably. These results open a novel route for the plant-free biosynthesis of gallic acid with potential applications across the food, cosmetic, and pharmaceutical industries.