Enhancement of fermentation process in Pu-erh tea by tea-leaf extract.

Pu-erh tea is known as a fermented tea and longer storage enhances its flavor and taste. Recently, Aspergillus, Blastobotrys, and Streptomyces are found to play important roles in nutritional enhancement of Pu-erh tea by fermentation. Since water and temperature affect the microbial growth, we therefore explored the factors that might enhance the Pu-erh tea fermentation. The results showed that the addition of fresh tea-leaf extract (TLE) enhanced the withered tea fermentation (at 37 degrees C, 80 to 85% RH) as compared with the water only. Contents of statin, GABA, gallic acid, DPPH scavenging and polyphenol oxidase (PPO) activities were increased, whereas polyphenols and caffeine were decreased over 6 mo. TLE dose-dependently enhanced some of the qualities (that is, statin, PPO) of Pu-erh tea significantly as compared with the water only. The effect was related to the increase population of A. niger and A. carbonarius at 6 mo (from 7.6 +/- 1.2 x 10(1) and 3.2 +/- 1.3 x 10(1) to 3.1 +/- 1.2 x 10(6) and 2.4 +/- 1.1 x 10(5) colony forming units [CFU]/g, respectively). After drying process (90 degrees C, 30 min), the total microbial count from these samples returned to background level (3 +/- 0.5 x 10(2) CFU/g). None of ochratoxin and fumonisin, toxins from Aspergillus, was detected in the final products. The flavor and taste were also enhanced by treatment with TLE. The inoculation with S. cinereus Y11 with 2% TLE further enhanced these functional contents (about 2-fold increase of statin level) in the experimental Pu-erh tea. Therefore, this result may add a new process for Pu-erh tea manufacture.