Isolation of mycotoxins producing black aspergilli in herbal teas available on the Swiss market

Black aspergilli are among the predominant fungal contaminants in herbal teas. Despite the ability of some species in this group to produce the mycotoxins ochratoxin A (OTA) and fumonisins no study had been done to investigate in detail their presence in this commodity. In the present work conventional herbal teas available on the Swiss market were investigated for black aspergilli contamination. Black aspergilli were found in 16 of 22 samples, ranging from 10 to 3500 colony forming units per gram of herbal tea. Recovered isolates were identified to the species level by calmodulin sequencing. The most frequently isolated species were Aspergillus niger, Aspergillus acidus, Aspergillus awamori and Aspergillus tubingensis. Aspergillus carbonarius, the most important OTA-producing black Aspergillus, could not be recovered. A. niger and A. awamori isolates were tested for their ability to produce fumonisins and OTA in vitro. Fumonisins were produced by 76% of A. niger and 37% of A. awamori isolates. 7% of A. niger and none A. awamori isolates could produce OTA. In total, 12 of 22 samples were found to be contaminated with black aspergilli able to produce major mycotoxins. Our results indicate that mycotoxins producing black aspergilli are widespread fungal contaminants of herbal teas. Therefore, their presence as well as the occurrence of their mycotoxins should be further investigated to assess health risks linked with the consumption of this commodity