Antimicrobial activity of tea as affected by the degree of fermentation and manufacturing season

Bacillus subtilis, Escherichia coli, Proteus vulgaris, Pseudomonas fluorescens, Salmonella sp. and Staphylococcus aureus were used to test the antimicrobial activity of tea flush extract and extracts of various tea products. Among the six test organisms, P. fluorescens was the most sensitive to the extracts, while B. subtilis was the least sensitive. In general, antimicrobial activity decreased when the extents of tea fermentation increased. The antimicrobial activities of tea flush extract and extracts of tea products with different extents of fermentation varied with test organisms. Tea flush and Green tea, the unfermented tea, exerted the strongest antimicrobial activity followed by the partially fermented tea products such as Longjing, Tieh-Kuan-Ying, Paochung, and Oolong teas. On the other hand, Black tea, the completely fermented tea, showed the least antimicrobial activity. It was also noted that extracts of Oolong tea prepared in summer exhibited the strongest antimicrobial activity, followed by those prepared in spring, winter and fall.