Inhibitory effects of tea extract on aflatoxin production by Aspergillus flavus

Aflatoxins, one of the most carcinogenic substances, have been implicated as a potential threat to the safety of tea beverages. In this study, we studied the inhibitory effects of the aqueous extracts from several Chinese traditional teas, such as green tea, black tea, flower tea, raw Puer tea (naturally fermented Puer tea) and Puer tea (inoculated Puer tea), on the growth and aflatoxin production of Aspergillus flavus. All the tested extracts inhibited the production of aflatoxin B1, whereas they did not inhibit mycelial growth of A.flavus. Considering the highest inhibitory effect of Puer tea extract on aflatoxin production, a semi-quantitative RT-PCR was designed to detect its impacts on the expression of genes responsible for the regulation of aflatoxin synthesis. The results showed that the transcriptions of both aflS and aflR were down-regulated to undetectable levels by the addition of Puer tea extract. This study indicated that most tea contained molecules inhibitory to aflatoxin production, which were very important factors for the risk assessment of tea exposed to aflatoxin. Some tea extracts could be developed as antiaflatoxin agents in food preservation. Significance and Impact of the Study Recently, safety concerns of the popular Puer tea have arisen because of aflatoxin contamination. In this study, we analysed the inhibitory effect of 30 tea aqueous extracts on the growth and aflatoxin production of Aspergillus flavus. Our results indicated that most tea inhibited aflatoxin production by down-regulating the transcription of aflR and aflS. The findings could contribute to the safety assessment of tea exposed to aflatoxin and provide some useful data concerning a new approach for controlling aflatoxin contamination.