DEVELOPMENT OF GRAPE POMACE-FLAVORED KOMBUCHA: EFFECTS OF SUGAR AND POMACE CONCENTRATIONS ON BIOACTIVE COMPOUNDS AND ANTIOXIDANT ACTIVITY

Kombucha is a fermented beverage produced by symbiotic culture of bacteria and yeast (SCOBY). The content of bioactive compounds and its potential health benefits has attracted interest of consumers and producers.  The use of grape pomace, a by-product rich in phenolic compounds, represents a sustainable strategy for improving the functional quality of kombucha and the valorization of this by-product. The objective of this study was to evaluate the influence of grape pomace and sugar concentrations, and fermentation time on the physicochemical characteristics, bioactive compounds, and antioxidant activity of flavored kombucha. The kombucha was prepared from green tea and subjected to primary fermentation (8 days), followed by secondary fermentation (14 days) with the addition of grape pomace at concentrations of 7.5%, 15%, or 30%, combined with 0, 25, or 50 g/L of sugar. The following parameters were evaluated: pH, total soluble solids (TSS), total titratable acidity (TTA), reducing sugars, total phenolic compounds (TPC), total flavonoids, monomeric anthocyanins, and antioxidant activity using the DPPH, ABTS, and FRAP methods. During the first fermentation, the pH decreased from 3.95 to 3.55, while the TTA increased from 0.07 to 0.15 g/100 mL, as expected by fermentation process. The flavonoid content increased from 0.192 to 0.357 mg quercetin equivalents/mL, and the antioxidant activity determined by the FRAP method varied from 0.898 to 1.835 mg Trolox equivalents (TE)/mL. In the second fermentation, the highest total phenolic compound content was observed in the formulation containing 15% of grape pomace and 25 g/L of sugar (1.613 mg GAE/mL). Although the formulations with 30% of grape pomace had higher anthocyanin contents, only the formulations containing 25 g/L of sugar maintained the stability of these pigments between days 0 and 7 (p > 0.05). FRAP values ranged from 9.05 to 10.55 mg TE/mL for formulations with 15% pomace and from 9.02 to 10.53 mg TE/mL for those with 30%, representing differences of less than 9% during fermentation. For formulations containing 50 g/L of sugar, this difference decreased to just 0.6% on the 14th day. In addition, all formulations reached a pH below 4.2 on the 11th day, in accordance to Brazilian legislation for kombucha. Overall, the 11th day of fermentation provided the best balance between acidification, preservation of bioactive compounds, and antioxidant activity. Although the 30% pomace concentration increased the anthocyanin content, the formulation containing 15% pomace exhibited similar levels of phenolic compounds, antioxidant capacity, and physicochemical characteristics, while using half the amount of raw material. Thus, this formulation proved to be the most viable alternative from technological, economic, and environmental perspectives for kombucha production. Acknowledgments: The authors thank the National Council for Scientific and Technological Development (CNPq) for the financial support provided for the development of this research.