Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/1997
Publication Date: N/A
Interpretive Summary: The fungus Aspergillus flavus infects maturing corn kernels and produces the highly toxic compound aflatoxin B1. To safeguard this part of the food supply and increase the value of the corn crop to growers, research was undertaken to determine if natural compounds occurring in corn could be used to help reduce the amount of aflatoxin in infected corn. A group of compounds, found in the yellow part of the seed of yellow corn, called carotenoids were found to inhibit formation of aflatoxin although growth of the fungus was not affected. The results obtained indicate that if corn lines producing moderate to high levels of carotenoids in the germ could be found then the overall level of aflatoxin in infected corn of these lines should be lower and the value and safety of corn grown in areas susceptible to A. flavus would be increased.
Technical Abstract: Carotenes and xanthophylls occurring in yellow corn and related terpenoids were tested for effect on growth and aflatoxin B1 production by Aspergillus flavus NRRL 3357 using the suspended disc culture method. Significant inhibition of aflatoxin synthesis was shown at levels of beta-carotene, lutein and zeaxanthin comparable to those found in horny endosperm. In most cases, growth was not affected. Inhibition was significantly greater for carotenoids with an alpha-ionone type ring (alpha-carotene and zeaxanthin) and for alpha-ionone as compared to beta-ionone. The presence of hydroxy groups on the rings tended to decrease inhibition but did not override the effect of the ring type; lutein was similar to alpha- carotene and zeaxanthin was similar to beta-carotene in inhibition. A mutant accumulating norsolorinic acid (NA), A. parasiticus SRRC 162, incubated with alpha-carotene produced both reduced levels of NA and aflatoxins indicating that inhibition occurred before NA. Additional A. flavus and A. parasiticus strains were tested against 50 ug/mL beta-carotene. The A. flavus strains had from 89% to 96% inhibition and were significantly more sensitive than NRRL 3357. A. parasiticus strains were less sensitive and generally similar or had lower inhibition than NRRL 3357. The results indicate that the presence of carotenoids in endosperm may decrease the amount of aflatoxin produced by A. flavus.