Oak (Quercus petraea) Leaf-Based Kombucha: A Sustainable Approach to Fermented Beverages

Kombucha is traditionally produced by fermenting black tea (<i>Camellia sinensis</i>), but exploring alternative plant materials could enhance sustainability and resource diversity. The study evaluated the potential of oak (<i>Quercus petraea</i>) leaves as a substrate for kombucha fermentation. Fresh and processed oak leaves were used to prepare kombucha infusions fermented for different time periods and compared with black tea kombucha, as well as unfermented infusions. Fermentation increased total phenolic content and antioxidant capacity in the dried and crushed leaf treatments, while lowering pH, which confirms effective acidification. Overall, beverages produced from dried and crushed oak leaves exhibited phenolic and antioxidant characteristics comparable to those of black tea kombucha. These findings suggest that <i>Q. petraea</i> leaves may represent a sustainable (due to the vast amount of raw material), same as not traditional alternative for kombucha production, contributing to the diversification of fermentation substrates in functional beverage development.