GREEN TEA KOMBUCHA ENRICHED WITH GRAPE PEEL PHENOLIC EXTRACT EXHIBITS ENHANCED PHENOLIC DIVERSITY AND ANTIOXIDANT ACTIVITY

Kombucha is a fermented beverage recognized for its high content of phenolic compounds and antioxidant properties. However, studies investigating the enrichment of kombucha with anthocyanin-rich plant extracts remain limited. In this study, a green tea kombucha enriched with a phenolic extract from BRS Vitória grape peel (GrPeK) was developed to enhance its phenolic composition and evaluate its ability to modulate intracellular reactive oxygen species (ROS) in different cell lines. Green tea kombucha was produced through fermentation using a symbiotic culture of bacteria and yeast (SCOBY) and subsequently enriched with 15% (v/v) grape peel phenolic extract. Total phenolic content was determined, and specific phenolic compounds were quantified by HPLC. Antioxidant activity was evaluated by measuring intracellular ROS levels using the DCFH-DA assay in CCD-18Co, Caco-2, HCT-8, and HepG2 cells. The addition of the grape peel extract increased the total phenolic content of the green tea kombucha from 0.72 to 0.94 mg GAE/mL, whereas the extract itself contained 1.95 mg GAE/mL. The phenolic profile of green tea kombucha was predominantly composed of proanthocyanidins and flavonols, especially procyanidin B2, quercetin-3-glucoside, and kaempferol-3-glucoside, which remained the major compounds in GrPeK. In contrast, the grape peel extract exhibited a distinct phenolic composition, characterized by a high diversity and concentration of anthocyanins. The GrPeK contained six anthocyanins that were absent in the green tea kombucha, including derivatives of malvidin, cyanidin, delphinidin, peonidin, and pelargonidin demonstrating greater chemical diversity. These compounds, highly abundant in the grape extract, were successfully incorporated into the kombucha matrix, resulting in a more complex phenolic profile. Additionally, compounds such as caftaric acid, not detected in the original kombucha, were identified in GrPeK, further highlighting the contribution of the grape peel extract. In cellular assays, the GrPeK significantly reduced intracellular ROS levels in HepG2 cells under all evaluated conditions and exhibited concentration-dependent antioxidant activity in the remaining cell lines, indicating its ability to modulate cellular redox homeostasis. Overall, the enrichment of green tea kombucha with grape peel phenolic extract increased the diversity of bioactive compounds, introduced anthocyanins absent from the original beverage, and enhanced its ability to modulate cellular oxidative stress. These findings highlight the potential of grape peel, an agro-industrial by-product, as a valuable functional ingredient for the development of fermented beverages with added value and promising applications in the food and health sectors.