Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 30, 1996
Publication Date: N/A
Interpretive Summary: A group of compounds called sterol esters occur in the outer layers, or bran, of corn and other cereal grains. These compounds, along with other unpurified mixtures from corn bran, were tested for their effect on insects which attack preharvest corn and the fungus which produces aflatoxin, a toxin for which control strategies are being investigated. The sterol esters had little effect on the insects but showed a significant capacity for increasing the level of aflatoxin produced by the fungus. The results suggest that corn lines low in these compounds might have lower toxin levels.
Technical Abstract: Steryl esters of ferulic and p-coumaric acids are localized in the inner pericarp and aleurone layers of corn and other cereals. Because of the location of these compounds, the atypical composition of the sterols esterified and the known inhibition of ferulic acid on aflatoxin synthesis, the possibility that these esters could be defensive compounds against corn fungal pathogens or insects was tested. Bioassays of pure ferulate esters and a complete ester fraction from both corn and rice showed no appreciable effect at 100 ppm on spore germination or germ tube growth of Aspergillus flavus, Fusarium moniliforme or Diplodia maydis. Sclerotinia sclerotiarum was inhibited by 75-90% by the total steryl ester fraction from corn and approximately 50% by the ester fraction from rice bran oil. The two major esters present in the corn mixture, stigmastanyl and campestanyl ferulate showed little or no inhibition. The complete steryl ester fraction from corn bran had no effect on corn earworm larvae or driedfruit beetle adults but driedfruit beetle larvae showed a significant increase in weight. The steryl ester fraction increased aflatoxin B1 level in A. flavus NRRL 6536 significantly at 0.33 and 1.0 mg/ml; aflatoxin B1 levels decreased at 3.33 mg/ml but remained higher than the control. No effect from the esters was found for A. flavus NRRL 3357. The steryl ferulate and p-coumarate ester fraction from corn was not inhibitory to the corn pathogens tested but it may increase the level of aflatoxin formation in corn infected with A. flavus.