INHIBITION OF AFLATOXIN B1 BIOSYNTHESISIN ASPERGILLUS FLAVUS BY ANTHOCYANIDINS AND RELATED FLAVONOIDS

Authors: Norton, Robert

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/1999
Publication Date: N/A
Citation: 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 occuring in corn could be used to help reduce the amount of aflatoxin in infected corn. A group of colored compounds called anthocyanins, and related colorless compounds, that occur in the outer layers of seeds of some types of corn, especially "indian corn," were tested for their effect on the fungus and found to inhibit formation of aflatoxin at levels of the compounds several times higher than those believed to occur in mature grain. Inhibition occured before any of the toxic precursors of aflatoxin were formed and growth of the fungus was not affected. The results indicate that higher levels of anthocyanins would need to be produced by corn to have an effect on aflatoxin levels and it would have to be made in the germ of the corn where most aflatoxin is produced by the fungus. Nevertheless, these compounds provide additional insight into the chemical structures of naturally occurring compounds inhibiting toxin production in corn.

Technical Abstract: Anthocyanin aglycones and precursor or related flavonoids were tested at concentrations from 0.3-9.7 mM (ca 0.1-3.0 mg/mL) for activity against growth and aflatoxin B, biosynthesis by Aspergillus flavus NRRL 3357. Aflatoxin B, production was inhibited by all anthocyanidins tested and 3-hydroxy compounds were more active than 3-deoxy forms. Monoglycosides of pelargonidin were 40% less inhibitory than the aglycone, whereas a monoglucoside and a diglycoside of cyanidin were 80% and 5%, respectively, as active as the aglycone. Of eight flavonolds tested, only kaempferol was moderately active, while luteolin and catechin were weakly inhibitory. Binary combinations of delphinidin and three other aflatoxin inhibitors acted independently of each other. Results with an aflatoxin pathway mutant indicated that anthocyanidin inhibition occurred before norsolorinic acid synthesis.