INFLUENCE OF TEA VARIETY (Camellia sinensis) ON CHANGES IN PHENOLIC CONTENT AND ANTIOXIDANT ACTIVITY OF KOMBUCHA DURING IN VITRO GASTROINTESTINAL DIGESTION

The beverage sector has been undergoing significant transformations, driven by the demand for products that combine flavor with health benefits. In this context, nonalcoholic beverages stand out for containing bioactive compounds of plant origin, such as teas, which are rich in catechins, flavonoids, and phenolic acids. Among them, kombucha stands out as a fermented beverage with functional potential, resulting from the fermentation of tea (Camellia sinensis) with sugar and a symbiotic culture of bacteria and yeast (SCOBY). The type of processing applied to Camellia leaves and buds determines the varieties of tea and can influence both the chemical composition and the bioaccessibility and bioactivity of the compounds. The main varieties include green, black, white, yellow, oolong, and red (pu-erh) teas. The present work aimed to evaluate how different types of tea influence the phenolic compound content and the antioxidant activity of kombucha throughout simulated gastrointestinal digestion. The kombuchas were prepared from the six aforementioned tea varieties, using 5 g of leaves per liter of water, 10% (v/v) starter liquid, SCOBY approximately 8 cm in diameter, mineral water, and 50 g/L of granulated sugar. The infusions were prepared at 80 °C for 10 minutes, with the fermentation process carried out for 16 days (14 aerobic and 2 anaerobic), at 25 °C. The beverages showed significant differences in total phenolic content and antioxidant activity, both before digestion and in the gastric and intestinal phases of the in vitro simulation. The yellow, green, and white tea kombuchas exhibited higher phenolic content, with values of 0.92, 0.84, and 0.73 mg GAE/mL before digestion, 0.97, 0.86, and 0.71 mg GAE/mL in the gastric phase, and 0.77, 0.62, and 0.50 mg GAE/mL in the intestinal phase, respectively. The yellow, green, red, and oolong tea kombuchas were notable for their high antioxidant activity, with initial DPPH values between 2.42 and 2.66 mmol TE/L, FRAP from 11.3 to 13.7 mmol FeSO₄/L, and ABTS⁺ from 10.6 to 11.6 mmol TE/L. During simulated digestion, all methods showed an increase in the gastric phase (up to 5.11, 14.8, and 13.3 mmol/L, respectively), followed by a slight reduction in the intestinal phase. In summary, all six kombuchas exhibited similar behavior, characterized by good stability of phenolic compounds and antioxidant activity throughout the simulated digestion. The observed variations were influenced by the type of tea used and may reflect differences in the composition and stability of the phenolic compounds.