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

< 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.