Abstract
We investigated ochratoxin A (OTA) contamination in raisin samples purchased from Slovak markets and determined the diversity of black-spored aspergilli as potential OTA and fumonisin (FB1 and FB2) producers. The taxonomic identification was performed using sequences of the nuclear ITS1-5.8s-ITS2 region, the calmodulin and beta-tubulin genes. We obtained 239 isolates from eight fungal genera, of which 197 belonged to Aspergillus (82%) and 42 strains (18%) to other fungal genera. OTA contamination was evidenced in 75% of the samples and its level ranged from 0.8 to 10.6 µg/kg. The combination of all three markers used enabled unambiguous identification of A. carbonarius, A. luchuensis, A. niger, A. tubingensis and A. welwitschiae. The dominant coloniser, simultaneously having the highest within-species diversity isolated from our raisin samples, was A. tubingensis. Out of all analysed strains, only A. carbonarius was found to produce OTA, but in relatively high quantity (2477–4382 µg/kg). The production of FB1 and FB2 was evidenced in A. niger strains only.
Highlights
Dried vine fruits are some of the most favourite and frequently utilised ingredients in the food industry; they are often exposed to contamination by metabolites of various microorganisms, including filamentous fungi [1]
We investigated Ochratoxin A (OTA) contamination of dried vine fruit packages of various origins purchased in Slovak markets and analysed the taxonomic diversity and the ochratoxin and fumonisin (FB1 and FB2) production ability of the black aspergilli strains isolated
Our study revealed that the remaining strains belonging to A. luchuensis, A. niger, A. tubingensis and A. welwitschiae did not produce OTA within in vitro tests
Summary
Dried vine fruits are some of the most favourite and frequently utilised ingredients in the food industry; they are often exposed to contamination by metabolites of various microorganisms, including filamentous fungi [1]. Members of the Aspergillus section Nigri [3] are considered to be some of the most influential food contaminants of dried vine fruit products worldwide. These microorganisms are well known as important producers. Members of the Aspergillus section Nigri were proven to be the main OTA (ochratoxin A) producers in grapes and are responsible for the contamination of wine, grape juice and raisins [5,6,7,8].
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