Development and Characterization of Kombucha Tea Nanoemulsion for Stability, Bioactive Delivery, and Functional Food Applications

Kombucha is a fermented tea beverage and a rich source of bioactive compounds with potential health benefits. This study aimed to evaluate the effects of different tea substrates (green, oolong, and black tea) on fermentation characteristics, bioactive compound profiles, antioxidant activity, and cytotoxicity, and to develop a nanoemulsion system for the encapsulation of kombucha-derived bioactive compounds for food applications. Kombucha was fermented for 15 days and during microbial growth, pH, total acidity, and sugar consumption were monitored. The results showed that green tea kombucha exhibited the lowest pH and highest total acidity, indicating more active fermentation. High-performance liquid chromatography analysis revealed that concentrated green tea kombucha contained higher levels of catechin, caffeine, and selected organic acids, whereas black tea kombucha exhibited the highest epigallocatechin gallate (EGCG) concentration. Among the tested samples, green tea kombucha demonstrated superior antioxidant properties as determined by DPPH, ABTS, and FRAP assays, while exhibiting no significant cytotoxicity in RAW 264.7, Caco-2, and A549 cells. Based on these findings, a nanoemulsion system was developed using concentrated green tea kombucha. The nanoemulsion exhibited an average particle size of 110.03 ± 6.2 nm, a polydispersity index of 0.28 ± 0.01, and a zeta potential of +32.5 ± 0.5 mV. Furthermore, the nanoemulsion maintained acceptable physicochemical stability during 6 months of storage at 4 °C, remaining within the nanoscale range with only minor changes in PDI and zeta potential. The encapsulation efficiency reached 91.66 ± 2.29%, and the system demonstrated a biphasic release profile with an initial burst followed by sustained release. Cellular uptake studies confirmed efficient internalization of the nanoemulsion in all tested cell lines. These findings highlight the potential of green tea kombucha as a functional food ingredient and demonstrate the feasibility of nanoemulsion-based systems for the encapsulation and cellular internalization of kombucha-derived bioactive compounds. This study provides a promising strategy for the development of value-added fermented beverages and functional food products.