Contamination of raisin by filamentous fungi – potential producers of ochratoxin A

The forty-one samples of Armenian made and eleven samples of imported raisins collected in several markets in Yerevan were studied. The sample collections were carried out during of years 2004 to 2008. Thirty two species of filamentous fungi from Aspergillus, Penicillium, Alternaria Trichoderma and Syncephalastrum genera were isolated and identified. Among species isolated from studied samples species belonging to Aspergillus genera have a very high frequency of occurrence, 65.2% of all investigated filamentous fungi. Species from Nigri section show the highest occurrence: 66.7% of all isolated fungi belonging to Aspergillus genera. Species A. carbonarius and A. niger were dominated among isolated fungi from section Nigri. Both Armenian and imported samples of raisin had a high contamination level by these fungi which are potential producers of ochratoxin A. In Armenian samples were detected two more ochratoxigenic species belonging to Aspergillus section Nigri: A. sclerotioniger and A. lacticoffeatus. But their frequency of occurred was low. Thirty seven strains of A. flavus were isolated, 92% of them were isolated from Armenian samples. Influence of рН and aw on contamination level of raisin by fungi was studied. It was revealed that highest contamination level by filamentous fungi occurred in raisins with relatively high aw value. Contamination level of raisin doesn't depend on pH