Mycotoxin contamination of Vietnamese coffee beans caused by Aspergillus sections Nigri and Circumdati

Abstract

Sixteen samples of Vietnamese coffee beans were examined for the presence of mycotoxigenic fungi that produce ochratoxins and fumonisins. Species of the strains isolated from the beans were tentatively identified by morphology as Aspergillus niger species complex (isolation frequencies of the beans: 56.6%), Aspergillus carbonarius (3.3%), and Aspergillus species in section Circumdati (2.9%). The strains randomly selected from the species were correctly identified by sequencing of the β-tubulin and/or mitochondrial cytochrome b gene. All of the strains of A. carbonarius and Aspergillus westerdijkiae, identified in section Circumdati, produced ochratoxin A (OTA). On the other hand, only one out of the 41 strains of A. niger produced a detectable level of OTA. Therefore, A. carbonarius and A. westerdijkiae, rather than A. niger, are likely to be the main sources of OTA contamination in the beans. With regard to A. niger, 37 out of the 41 strains produced fumonsin B2 (FB2). LC-MS/MS analysis of the 16 bean samples showed that 3 samples were contaminated with OTA and/or FB2; one Arabica sample with OTA (2.3 μg/kg), another with FB2 (55 μg/kg), and one Robusta sample with both OTA (6.3 μg/kg) and FB2 (49 μg/kg). These results demonstrate that Vietnamese coffee beans are commonly infected with OTAand FB2-producing fungi and occasionally co-contaminated with these mycotoxins.