Optimization of Kombucha Fermentation from Green Tea and Pineapple Juice: Chemical, Physicochemical, and Bioactive Profiles for Functional Beverage Development

This study evaluated the metabolic evolution and functional quality of green tea-based kombucha and pineapple juice-based kombucha fermented with the same symbiotic culture of bacteria and yeasts. Beverages were monitored over 0, 3, 5, and 7 days of fermentation using nuclear magnetic resonance spectroscopy alongside complementary physicochemical and color analyses to elucidate changes in organic acids, amino acids, and phenolic compounds. Both beverages showed progressive pH reduction to approximately 3.4, increased titratable acidity, and lightning of color (increased L, decreased a and b*) over time. Sucrose content decreased progressively in both systems, accompanied by ethanol production followed by oxidation to acetic, gluconic, and succinic acids, which increased significantly (p < 0.05). Pineapple juice-based kombucha exhibited higher total acid production and faster acidification, while green tea kombucha maintained greater stability in malic and citric acids. Among nitrogenous and phenolic compounds, epicatechin gallate (ECG) and epigallocatechin-3-gallate (EGCG) peaked at day 5 before declining due to oxidative degradation; theanine and alanine showed transient increases, indicating microbial synthesis and assimilation. Caffeine remained relatively stable throughout fermentation. Antioxidant activity measured by the ABTS assay revealed significantly higher radical scavenging capacity in green tea kombucha (10.36 μmol TE/g at day 0 to 10.33 μmol TE/g at day 7) compared to pineapple kombucha (1.90 μmol TE/g to 3.00 μmol TE/g over the same period). Overall, day 5 was identified as the optimal fermentation point, balancing acid production, pH reduction, and preservation of bioactive compounds, supporting the development of functional kombucha beverages from both tea and fruit matrices.