BIOACCESSIBILITY OF BIOACTIVE COMPOUNDS AND ANTIOXIDANT CAPACITY OF KOMBUCHA FLAVORED WITH 15% GRAPE RESIDUE

Kombucha is a beverage rich in bioactive compounds, traditionally prepared using Camellia sinensis tea added with sugar and fermented by SCOBY (symbiotic culture of bacteria and yeast). The incorporation of alternative raw materials into kombucha is a promising strategy to enhance its bioactive profile and diversify its sensory characteristics. Thus, this study aimed to develop and characterize kombucha flavored with grape pomace and to evaluate the influence of in vitro gastrointestinal digestion on the bioaccessibility of bioactive compounds and the antioxidant capacity of the resulting beverage. The first-fermentation kombucha, unflavored (K0), was prepared using green tea and granulated sugar and fermented for 8 days. Subsequently, a grape residue infusion was added in equal proportion, and fermentation continued for another 10 days, resulting in a kombucha flavored with 15% grape residue (K15). The samples were characterized by pH, total titratable acidity, total soluble solids, and reducing and non-reducing sugars. Bioactive compound analysis involved measuring total phenolic compounds, total flavonoids, and total monomeric anthocyanins, while antioxidant capacity was assessed using the DPPH, ABTS, and FRAP methods. In vitro simulated digestion followed the INFOGEST protocol, and the identification of the compounds was analyzed by High-Performance Liquid Chromatography (HPLC). The pH of the kombucha samples was within the established parameters for the beverage (2.5 - 4.2). In K0, non-reducing sugars (480.23 mg glucose/mL) predominated and reducing sugars (20.65 mg glucose/mL) were minority. Meanwhile, K15 showed more of reducing sugars (345.48 mg glucose/mL) than non-reducing sugars (103.54 mg glucose/mL), due to the addition of grape residue. Prior to simulated digestion, flavoring with grape residue reduced the content of phenolic compounds in 19.61% and flavonoids in 18.85%, compared to K0. However, after digestion, the bioaccessibility of phenolics and flavonoids in K0 (7.32% and 12%, respectively) was lower than in K15 (14.23% and 20.94%, respectively), suggesting better retention of compounds resulting from the addition of grape residue. A reduction of 98.08% in anthocyanin content was also observed, after digestion. Regarding antioxidant activity, the behavior observed in the FRAP assay was very similar to the phenolic and flavonoid content. Using the DPPH method, the reduction in antioxidant capacity after digestion was 53.27% for K0 and 46.73% for K15, reinforcing the protective effect of adding grape residue. Vanillic and t-cinnamic acids were found in K0 and K15, before and after digestion. Cyanidin chloride also remained detectable in non-digested and digested K15. Therefore, the addition of grape residue enriches and influences the levels and content of bioactive compounds, particularly anthocyanins. The flavoring stage enabled K15 to exhibit better preservation of phenolics and flavonoids compared to K0, even after simulated digestion, highlighting the utilization and applicability of grape residue in kombucha production. Acknowledgments: Araucária Foundation (FAPPR).