Efficacy of Fermented Teas in Antibacterial Activity

Abstract

Fermented tea or “Kombucha” was prepared by a tea broth (1.7 % w/v) and sucrose (10% w/v) with supplement of commercially available starter culture. Teas used in this study were mulberry tea, Japanese green tea, Jasmine tea, Ulong tea and black tea. The teas were fermented for two weeks as an inoculum, following by inoculation to another tea broth and required further two-week static fermentation. In this study the antibacterial activity of several teas were tested against pathogenic bacteria in human and shrimp (e.g. Vibrio cholerae, Salmonella typhi, Pseudomonas aeruginosa, Vibrio harveyi, Vibrio parahaemolyticus, Vibrio alginolyticus and Vibrio vulnificus) by disc agar diffusion assay. The pH of fermented teas decreased from around 5 to 2 and the OD₆₀₀ of tea broth rose significantly from around 0 to 1.5 during fermentation period. Broth from black tea poses the greatest inhibitory activity by measuring diameters of inhibition zones. V. parahaemolyticus showed the largest susceptibility to the
fermented tea while pathogenic bacteria in human appeared to be less sensitive. Changes in major components of tea broth were also observed by HPLC analysis. The key organic acids such as succinic acid and gluconic acid produced during the period increased with time, proving the major role of these acids in the microorganism’s growth inhibition.