Improved Antioxidant Properties and Vitamin C and B12 Content from Enrichment of Kombucha with Jujube (Ziziphus jujuba Mill.) Powder

(1) Objectives: Traditional kombucha (K) is a fermented beverage obtained from black or green tea infusion. Besides traditional substrates, the possibility of using alternative ingredients resulted in changes in metabolic profile and biological activity. The aim of this work was to study an alternative kombucha (KJ) prepared by the addition of jujube powder to black tea. (2) Materials and Methods: Changes in pH, protein, sugars, phenolic (TPC), flavonoid (TFC), and vitamin C and B12 content were evaluated at different time points over a period of 45 days. The identification of polyphenols by HPLC DAD and the antioxidant capacity by DPPH, ABTS, and FRAP tests of all samples was also carried out. (3) Results: The results showed higher protein, total phenolic content, and antioxidant capacity in KJ samples than in K ones. Vitamin C content increased during fermentation and reached its maximum concentration on day 45 (7.1 ± 0.3 mg/100 mL) for KJ. Caffeine in the supplemented samples was the main biocompound among those identified. Vitamin B12 formed on day 4 in K and after 24 h in KJ samples, remaining constant at the initial value of 2.30 ± 0.01 mg/100 mL up to day 45. (4) Conclusions: The results highlight that the fortification of kombucha with jujubes improved its biological activity and the content of bioactive compounds.