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United States Department of Agriculture

Agricultural Research Service

Research Project: Environmental and Ecological Approaches to Eliminate Fungal Contamination and Mycotoxin Production in Plant Products

Location: Foodborne Toxin Detection and Prevention

Title: Distribution and mycotoxigenic potential of Aspergillus section Nigri species in naturally-contaminated almonds

Authors
item Palumbo, Jeffrey
item O Keeffe, Teresa

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 9, 2012
Publication Date: April 1, 2013
Repository URL: http://
Citation: Palumbo, J.D., O Keeffe, T.L. 2013. Distribution and mycotoxigenic potential of Aspergillus section Nigri species in naturally-contaminated almonds. Journal of Food Protection. 76:702-706.

Interpretive Summary: During almond processing, nuts with unacceptable amounts of mechanical or insect damage are removed. These “pick-outs” are more likely to be contaminated with aflatoxin, which is one reason they are regarded as inedible. In recent work, a group of almond pick-out samples were screened for Aspergillus flavus, and in the process, it appeared that they also contained black-spored Aspergillus species. Certain black-spored Aspergillus species produce ochratoxin or fumonisin, two important mycotoxins with human health implications. We examined strains of black-spored Aspergillus from these nut samples, to identify their species and determine whether they make either of these mycotoxins. None of the fungi we isolated made any ochratoxin, even though 3 of 21 almond samples contained ochratoxin. This indicates that other fungal species present on the nuts might be responsible for ochratoxin contamination. We found a large number of fumonisin-producing strains, which could also make fumonisin on almond agar, but none of the almond samples contained fumonisin. This suggests that even if fumonisin-producing fungi are present, the environment of the almonds is not suitable for fumonisin to be made.

Technical Abstract: In a previous study, inedible almond pick-out samples were assayed for aflatoxin and aflatoxigenic Aspergillus species. These samples were observed to contain high populations of black-spored Aspergillus section Nigri species. To investigate whether these species may contribute to the total potential mycotoxin content of almonds, Aspergillus section Nigri strains were isolated from these samples, and assayed for ochratoxin A (OTA) and fumonisin B2 (FB2). The majority of isolates were identified as A. tubingensis, which do not produce either mycotoxin. Of 47 A. niger and A. awamori isolates, 34 strains (72%) produced FB2 on CY20S agar, and representative strains produced lower, but measurable, amounts of FB¬2 on almond meal agar. No OTA-producing strains of Aspergillus section Nigri were isolated. Almond pick-out samples contained no measurable FB2, suggesting that properly dried and stored almonds are not conducive for FB2 production by resident A. niger and A. awamori populations. On the other hand, 3 of 21 samples contained low levels (<1.5 ng/g) of OTA, indicating that sporadic OTA contamination may occur, but may be caused by OTA-producing strains of other Aspergillus species.

Last Modified: 4/20/2014
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