The mechanism on decreasing the microbiological contamination of superfine green tea powder by ball milling

The present study compared the microbial population in the samples of steamed green tea and its superfine green tea powder by determining and analyzing microbial changes during ball milling, which is the key step of producing superfine green tea powder. The results showed that after ball milling the microbial counts of superfine green tea powder were dramatically decreased than steam green teas in which the total aerobic count were more than 104 CFU/g in 14/19 samples. With the duration of ball milling, the microbial population of superfine green tea powder was correspondingly decreased till below 103 CFU/g. To study the mechanism of ball milling on microbial counts' decreasing, a mold strain was isolated, purified and identified from the samples. Subsequently, the mold strain was cultured and individually ball-milled. The results indicated that fungal cell wall was disrupted and then microbial DNA was released during the process. Moreover, microbial populations in the tea samples were negatively correlated with cell wall breakage ratio. It was suggested that the ball milling was effective strategy for controlling the microbial contamination during the processing of superfine green tea powder.