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Postharvest Pathology and Mycotoxins

Suppression of Aspergillus flavus in Raisins by Solar Heating During Sun Drying. A. M. Hussein, Former graduate research assistant, Department of Pomology, University of California, Davis 95616, Present address: Assistant professor, Department of Horticulture, University of Alexandria, Egypt; N. F. Sommer(2), and R. J. Fortlage(3). (2)(3)Postharvest pathologist, and research associate, Department of Pomology, University of California, Davis 95616. Phytopathology 76:335-338. Accepted for publication 31 October 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-335.

Aflatoxin was readily produced in fresh grape berries needle inoculated with conidia of Aspergillus flavus, reaching 2,781 μg/kg after 6 days at 25 C. By contrast, aflatoxin reached only 147 μg/kg during the same period when conidia were inoculated into a small lesion caused by Botrytis cinerea. Fresh berries inoculated with the same conidial concentration of A. flavus and equal numbers of conidia of B. cinerea and Cladosporium herbarum accumulated an intermediate concentration of aflatoxin. During sun drying in the field, failure of germinating conidia of A. flavus to survive internal berry temperatures of 45-50 C or higher may explain the lack of aflatoxin in raisins and inability to reisolate A. flavus from test berries. In vitro tests demonstrated that exposure of germinating conidia of A. flavus for 30 min at 45 and 50 C reduced survivors to 0.7 and 0.025%, respectively. Internal berry temperatures during sun drying exceeded those temperatures on days with afternoon temperatures of 35 C or higher.

Additional keywords: Aspergillus parasiticus, mycotoxins, Vitis vinifera.