Characteristic fungi observed in the fermentation process for Puer tea

The fermentation process for Puer tea, a unique Chinese tea produced by microbial activities, was investigated by physicochemical and microbial analyses. The temperature of a windrow-shaped pile of tea leaves increased instantly at the beginning of fermentation and stayed at around 50 °C until day 35, then decreased gradually to room temperature at the end of fermentation, at day 50. Water content was approximately 30% or less, and pH value was maintained at a weakly acidic level of 5 to 6 throughout the fermentation, conditions that are favorable for propagation of fungi including yeasts. Polyphenol, the characteristic component of tea leaves, decreased continually from day 10 to day 50 of fermentation, corresponding well with the fact that the total concentration of fungi steadily increased during the same period. PCR followed by denaturing gradient gel electrophoresis (DGGE) analysis revealed that there were at least two major fungi: Aspergillus niger, which has been well known among Puer tea manufacturers, and Blastobotrys adeninivorans, which is newly recognized in the present study. Furthermore, both of these fungi were observed in the DGGE fingerprint when other commercial Puer tea products were analyzed. These results prompted us to deduce that both A. niger and B. adeninivorans play important roles in the nutritional enhancement of tea leaves during Puer tea fermentation.