Kombucha Fermentation Remodels the Phytochemical Composition of Gooseberry Juices and Reveals a Divergence Between Phenolic Abundance and HepG2 Cell Growth Inhibition

Kombucha fermentation can modify the phytochemical composition and biological properties of fruit-based beverages, although these changes may differ depending on the fermentation substrate. This study investigated the effects of 10-day kombucha fermentation using a symbiotic culture of bacteria and yeast (SCOBY) on red and white gooseberry (Ribes uva-crispa) juices supplemented with sucrose or buckwheat honey. Physicochemical characteristics, phenolic and volatile profiles, antioxidant capacity, enzyme inhibitory activities, HepG2 cell growth, gene expression, and sensory acceptance were evaluated. Fermentation decreased sugar concentrations and increased organic acid and ethanol contents. The concentrations of several flavan-3-ols, including epigallocatechin and epigallocatechin gallate, increased, whereas selected oligomeric procyanidins decreased. Red gooseberry beverages were characterized by a greater contribution of esters to their volatile profiles, while alcohols predominated among the identified volatile compounds in white gooseberry beverages. Red gooseberry formulations generally exhibited higher phenolic concentrations and antioxidant capacity, with the honey-supplemented variant showing particularly high values. However, phenolic-enriched extracts isolated from fermented white gooseberry beverages inhibited HepG2 cell growth more strongly than extracts from red gooseberry beverages. White gooseberry extracts also altered the expression of selected genes associated with metabolism and cancer-related signaling. Sensory evaluation indicated the highest overall acceptance for sucrose-supplemented red gooseberry juice. These findings demonstrate that the effects of kombucha fermentation depend on gooseberry juice type and carbon source, and that phenolic abundance and antioxidant capacity do not necessarily predict cellular growth-inhibitory effects or sensory acceptance.