Skip to main content
ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Foodborne Toxin Detection and Prevention Research » Research » Publications at this Location » Publication #310181
Title: Occurrence of ochratoxin a contamination and detection of ochratoxigenic aspergillus species in retail samples of dried fruits and nuts

Author
item Palumbo, Jeffrey - Jeff
item O Keeffe, Teresa
item Ho, Yvonne
item SANTILLAN, CARLO - Former ARS Employee

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/8/2014
Publication Date: 4/1/2015
Publication URL: http://handle.nal.usda.gov/10113/60886
Citation: Palumbo, J.D., O Keeffe, T.L., Ho, Y.S., Santillan, C.J. 2015. Occurrence of ochratoxin a contamination and detection of ochratoxigenic aspergillus species in retail samples of dried fruits and nuts. Journal of Food Protection. 78(4):836-842. doi: 10.4315/0362-028X.JFP-14-471.

Interpretive Summary: Ochratoxin A (OTA) is a toxic chemical produced by several Aspergillus species that are commonly found on many different types of food including dried fruits and tree nuts. Consequently, it is important to understand the frequency with which OTA may contaminate foods, and at what levels the contamination may occur. As part of a larger, multi-commodity study, we received samples of raisins, dates, figs, prunes, almonds, pistachios and walnuts from collaborating labs across the U.S. Samples were purchased from large and small stores, and were either bulk products or packaged products. Out of 666 total samples we analyzed, OTA was found in 48 raisin samples, 4 fig samples, 4 pistachio samples, and 1 date sample. In the samples containing OTA, levels of the toxin ranged from 0.28 to 15.34 parts per billion in contaminated raisins, figs and dates, and from 1.87 to 890 parts per billion in contaminated pistachios. The maximum allowable limit for OTA in dried fruit in the European Union is 10 parts per billion, and two raisin samples and one pistachio sample contained OTA at higher levels than that. To discover which fungi may be associated with OTA contamination in these samples, PCR reactions that specifically amplify target gene fragments from Aspergillus species that may make OTA were performed. PCR results showed that A. niger, A. welwitschiae, and A. carbonarius could be detected in some of the OTA-contaminated samples. Using classical microbiological techniques, OTA-producing A. carbonarius was isolated from only one of those samples, and no other OTA-producing fungi were isolated. These results will be useful in determining the risk of OTA exposure from different foods in the U.S., and in devising methods to discover the fungi responsible for OTA contamination in retail foods.

Technical Abstract: Ochratoxin A (OTA) is a mycotoxin produced by several species of Aspergillus and Penicillium and is a potential contaminant of a wide variety of food products. To determine the incidence of OTA contamination in dried fruits and tree nuts, retail packaged and bulk raisins, dates, figs, prunes, almonds, pistachios and walnuts were collected from small and large supermarkets in seven areas of the U.S. between 2012 and 2014. Of the 666 samples analyzed, OTA was detected in 48 raisin samples, 4 fig samples, 4 pistachio samples, and 1 date sample. OTA contamination levels ranged from 0.28 to 15.34 ng/g in dried fruits, and 1.87 to 890 ng/g in pistachios, with two raisin samples and one pistachio sample exceeding the E.U. regulatory limit of 10 ng/g. PCR detection of potential OTA-producing Aspergillus species showed the presence of A. niger, A. welwitschiae, and A. carbonarius in 20, 7, and 7, respectively, of the 57 OTA-contaminated samples. However, OTA-producing A. carbonarius was isolated from only one raisin sample, and no other OTA-producing Aspergillus species were found.