Evaluation of physicochemical, phenolic profile and antioxidant capacity changes of kombucha during fermentation

Kombucha is a slightly sweet, tangy, and effervescent fermented beverage that has recently become popular due to its reported health advantages. However, more research is needed to understand these potential benefits fully. This study aimed to determine the physicochemical and bioactive compound changes and the total antioxidant capacity of black tea kombucha during fermentation. The pH and total acidity were evaluated during sixteen fermentation days. As could be expected, pH reduced from an initial 4.70 ± 0.03 to 2.86 ± 0.03 while total acidity increased from 0.60 ± 0.04 to 11.62 ± 0.20 g L-1. High performance liquid chromatography in tandem mass spectroscopy (HPLC-MS/MS) was successfully developed to analyse the changes of target constituents (carbohydrates, organic acids, phenolic compounds), resulting in the detection of twenty-four compounds. HPLCMS/MS results further verified that lactic and acetic acid content increased as fermentation progressed. Sucrose content decreased, while changes in the most abundant phenolic substances revealed different patterns. The total phenolic content (TPC) and antioxidant capacity were evaluated with the Folin-Ciocalteu method, ABTS radical scavenging and CUPRAC assays. During fermentation, the TPC increased from 525 ± 3 (day 0) to 721 ± 2 µg GAE mLE−1 (day 16th). In the ABTS assay, the capacity of kombucha increased from 1527 ± 146 to 1767 ± 35 mg TE mLE−1 by the 9th day, then decreased to 1467 ± 123 mg TE mLE−1 by the 16th day. In contrast, no significant changes in the antioxidant capacity were observed in the CUPRAC assay. Understanding and analysing physicochemical and bioactive compound changes in kombucha during fermentation can help develop kombuchas with higher bioactive potential and improve knowledge on the kombucha fermentation process.