Aspergillus on tree nuts: incidence and associations |
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Authors: | Bayman Paul Baker James L Mahoney Noreen E |
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Institution: | (1) USDA ARS Western Regional Research Center, 800 Buchanan St., Albany, CA, 94710, U.S.A |
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Abstract: | California exports tree nuts to countries where they face stringent standards for aflatoxin contamination. Trade concerns
have stimulated efforts to eliminate aflatoxins and Aspergillus flavus from almonds, pistachios and walnuts. Incidence of fungi on tree nuts and associations among fungi on tree nuts were studied.
Eleven hundred pistachios, almonds, walnuts and brazil nuts without visible insect damage were plated on salt agar and observed
for growth of fungi. Samples came both from California nut orchards and from supermarkets. To distinguish internal fungal
colonization of nuts from superficial colonization, half the nuts were surface-sterilized before plating. The most common
genera found were Aspergillus , Rhizopus and Penicillium . Each species of nut had a distinct mycoflora. Populations of most fungi were reduced by surface sterilization in all except
brazil nuts, suggesting that they were present as superficial inoculum on (rather than in) the nuts. In general, strongly
positive associations were observed among species of Aspergillus ; nuts infected by one species were likely to be colonized by other species as well. Presence of Penicillium was negatively associated with A. niger and Rhizopus in some cases. Results suggest that harvest or postharvest handling has a major influence on nut mycoflora, and that nuts
with fungi are usually colonized by several fungi rather than by single species.
This revised version was published online in June 2006 with corrections to the Cover Date. |
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Keywords: | aflatoxin Aspergillus mycotoxin Penicillium Rhizopus |
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