Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2010
Publication Date: 4/1/2011
Citation: Palumbo, J.D., O Keeffe, T.L., Mcgarvey, J.A. 2011. Incidence of fumonisin B2 production within Aspergillus section Nigri populations isolated from California raisins. Journal of Food Protection. 74:672-675.
Interpretive Summary: Black-spored Aspergilli, including Aspergillus niger, A. tubingensis, and A. carbonarius, are fungi normally found on grapes and raisins, where they sometimes cause black rot diseases. Even without disease, these fungi have the potential to form mycotoxins including ochratoxin A and fumonisin B2. Fumonisin B2 is a mycotoxin originally described as a product of Fusarium species, but recently has been shown to be produced by A. niger. We isolated and screened 389 black Aspergillus strains from raisin vineyard samples to measure the frequency and amount of fumonisin B2 production by these fungi. We identified 194 strains as A. niger, and two-thirds of them produced detectable amounts of fumonisin B2. Out of 175 A. tubingensis strains, 9 produced fumonisin B2. Using PCR primers to two genes involved in fumonisin synthesis, we detected these genes in nearly all A. niger strains, both fumonisin producers and non-producers, indicating that the presence of these genes is not useful in predicting which strains produce fumonisin.
Technical Abstract: Fungi belonging to Aspergillus section Nigri occur frequently and in high populations on grapes. Species within this section include A. niger, A. tubingensis, and A. carbonarius, and are potential sources for mycotoxins including ochratoxin A and fumonisin B2 (FB2) in grapes and grape products. Aspergillus section Nigri strains were isolated from California raisins to examine the frequency and extent of FB2 production. Of 389 strains isolated, 194 strains were identified as A. niger, 128 of which produced FB2. An additional 175 strains were identified as A. tubingensis, nine of which produced FB2. These strains produced from 0.7 µg/ml to 17 µg/ml of FB2 in culture. PCR amplification of fum1 and fum19 gene fragments indicated that all FB2-producing strains and nearly all non-producing strains of A. niger contain these genes. In contrast, amplification of these genes from A. tubingensis was sporadic, suggesting low sequence homology between species. These results indicate that FB2 production is common among field isolates of A. niger, and suggest that the potential for FB2 contamination of California raisins needs to be addressed further.