Use of Response surface methodology to investigate the effect of several fermentation conditions on the antibacterial activity of several kombucha beverages.

This study aimed to investigate the effect of sugar concentration and fermentation time on the antibacterial activity of kombucha beverages prepared with four herbal teas. Four types of herbal teas including, black and green tea, lemon verbena, and peppermint were prepared then sweetened with 2, 5, and 8% sugar. The herbal teas inoculated with actively kombucha culture and after 7, 14, and 21 days, the antibacterial activity of the supernatant of beverages was evaluated against four bacteria based on agar well diffusion method. RSM was used to investigate the effect of fermentation time, sugar concentration, and tea type on the antibacterial activity of beverages. Sugar concentration and fermentation time showed a significant effect on the antibacterial activity of beverages-against all tested bacteria and type of herbal tea affected the antibacterial activity of beverages-against E. coli and S. aureus . Kombucha prepared with black tea at sugar 8% and fermentation time of 21 days showed the most antibacterial activity against B. cereus. The most antibacterial activity against S. aureus was observed in kombucha beverages prepared with green tea and peppermint for fermentation time of 21 days, at 2% and 8% sugar, respectively. Prepared beverages with peppermint and lemon verbena at 8% sugar and 21 days of fermentation showed the most antibacterial activity against E. coli and S. dysenteriae respectively. Generally, to achieve the highest antibacterial activity against the tested bacteria recommended preparation of kombucha beverages at the sugar of 8% and fermentation time of 21 days.