Microbial composition of four kinds of tea with different degree of oxidation

Sammanfattning: In this study, four representative kinds of tea have been studied: Tie guan yin, Light oolong tea, Dark oolong and Pu-erh (oxidation degree from low to high). The microbial contents of four kinds of tea were analyzed under normal condition (without brewing) and after brewing. Fully oxidized Pu-erh tea is the only tea that has undergone the fermentation process and has the highest bacterial counts as well as the most diverse bacterial composition, whereas Dark oolong rarely showed any microbial content. Most of the identified bacteria belonging to the family Bacillaceae, Staphylococcaceae and Paenibacillacea are soil-dwelling (naturally occur in soil) bacteria or a part of skin flora. The microbial analysis of four kinds of tea brewed at 90 °C indicated that no survived microorganisms could be detected in the brewed tea except for Pu-erh. Moreover, a potential probiotic Bacillus coagulans was found as the major bacteria in the brewed Pu-erh tea. Some of Bacillus coagulans isolates were brewed directly with hot water. The result showed that Bacillus coagulans could not survive at 90 °C without the protection of Pu-erh tea leafs. These isolates were also analyzed using RAPD (Random Amplified Polymorphic DNA) method. The result showed that most of them are different strains.