The effects of cold storage of table grapes, sulphur dioxide and ethanol on species of black Aspergillus producing ochratoxin A


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Table grapes of cv. ‘Superior’ were sampled from four vineyards during three seasons, for the occurrence of black Aspergillus species that can produce ochratoxin A after storage. The ochratoxin A-producing fungus, Aspergillus carbonarius, was identified in all the samples at harvest and it survived through cold storage. Storage of table grapes for 7 days at 20 °C resulted in occasional increase in the number of isolates recovered from the berries. In contrast, storage for 1 month at 0 °C, with sulphur dioxide (SO2) generator pads reduced the number of isolates significantly or completely, depending on the dose. Dipping the clusters in ethanol prior to cold storage did not reduce the number of isolates of the Aspergillus niger aggregate after storage. Exposure of A. carbonarius to a final level of 0.4 ppm of SO2 resulted in fewer fungal colonies than in the control, and the surviving spores developed into fungal colonies that failed to sporulate. These results demonstrate that A. carbonarius is ubiquitous on table grapes before storage and care should be taken to avoid its contamination.