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

English. 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.

English. Nowadays, tea is becoming more and more popular worldwide due to its attractive taste and health benefits on the human body. There is a variety of tea which can be mainly divided into four types depending on different degrees of oxidation. Generally speaking, green tea has the lowest degree of oxidation while Light oolong and Dark oolong are semi-oxidized with degrees of oxidation ranging from 10 % to 29 %, 60 % to 70 % respectively. Dark tea is completely oxidized with 100 % oxidation degree. The chemical components of tea such as phenolic substances have been well explored and studied. Nevertheless, a very few studies have been performed focusing on the microbial composition of tea as well as its health effects. Therefore the analysis of microbial composition of different kinds of tea has been performed. 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). Firstly, the microbial contents of four kinds of tea were analyzed under normal condition (without 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. After that, four kinds of tea were brewed at 90 °C and the microbial analysis indicated that no survived microorganisms could be detected in the brewed tea except for Pu-erh. More surprisingly, a potential probiotic Bacillus coagulans was found as the major bacteria in the brewed Pu-erh tea. Some of these 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 have different band pattern. Nevertheless, further investigations regrading strain type and characteristic of these Bacillus coagulans isolates are required. In conclusion, the fermented Pu-erh tea can provide beneficial bacteria (Bacillus coagulans) in addition to polyphenols to human body.