Kombucha is a traditional health beverage produced by fermenting sweetened tea with a symbiotic culture of bacteria and yeasts. Consumption of kombucha beverages has been growing and there is kombucha commercially available worldwide as one of the most famous low-alcohol beverages. Kombucha beverages have been claimed to have beneficial effects on human health because they contain a variety of bioactive compounds that possess various functional properties. At present, several kinds of raw material (e.g., milk, fruit, vegetables, and herbs) have been fermented with kombucha consortium and consumed as kombucha beverages. Although several studies have been written regarding the biological activities of kombucha and raw materials, there is however little information available on the characterization of their components as well as the biological activities of fermented kombucha from many raw material mixtures. Several pharmacological activities were reviewed in the scientific literature, describing their potential implications for human health. In addition, the adverse effects and toxicity of kombucha consumption were also reviewed. In this study, we focused on the main and latest studies of the pharmacological effects of kombucha beverages produced from various kinds of raw materials, including antioxidant, anti-inflammatory, immunomodulatory, antimicrobial, anticancer, antidiabetic, antihypertensive, and antihyperlipidemic effects in in vitro and in vivo studies.

Kombucha is a functional beverage fermented by the symbiosis of bacteria and yeasts and is comprised mainly of bioactive compounds and acids that have beneficial health effects. Our research aimed to determine the optimal ratio of co-culture of the bacterium Acetobacter pasteurianus AJ605 and the yeast Zygosaccharomyces bailii YN403 for kombucha fermentation in order to improve the consistency of kombucha quality so that it can be mass produced. Microbial growth, chemical characteristics, and antioxidant activities of kombucha during fermentation were analyzed. The results showed that a co-culture ratio of 8:2 (v/v) of A. pasteurianus AJ605 and Z. bailii YN403 gave the highest antioxidant activity after 10 days of fermentation, with a DPPH IC₅₀ value of 25.76 µl/mL and an ABTS IC₅₀ value of 8.84 µl/mL. The co-culture ratio of 8:2 showed antioxidant activity that was not significantly different (p>0.05) from that of SCOBY (symbiotic culture of bacteria and yeasts) alone. Additionally, during fermentation, the pH of kombucha decreased to 3.16, with increases in titratable acidity and alcohol content of 7.00 g/L and 7.96 g/L, respectively. To enhance the antioxidant activity and taste quality of kombucha, black tea and roselle were mixed at various ratios and inoculated with 10% (v/v) optimal co-culture. The results showed that a high antioxidant activity was obtained using an 8:2 (w/w) ratio of black tea and roselle, at day 10 of fermentation, with a DPPH IC₅₀ value of 23.88 µl/mL and ABTS IC₅₀ value of 6.11 µl/mL. Moreover, the results indicate that kombucha from black tea and roselle can be a functional beverage that has high antioxidant activity and sensory acceptability. Keywords: antioxidant; black tea; co-culture; kombucha; roselle *Corresponding author: Tel.: (+66) 23298400 Fax: (+66) 23298427 E-mail: daungjai.oc@kmitl.ac.th