Tasty Nuts' Natural Defense: Caffeic Acid?

Healthful nuts like almonds, pistachios and walnuts pass rigorous tests before they make their way into your shopping cart. The tests ensure that the nuts are free of unsafe levels of a natural, cancer-causing compound called aflatoxin.

A fungus, or mold, known as Aspergillus flavus is a leading source of the toxin. Now, Agricultural Research Service scientists and their colleagues have discovered that another natural compound, an antioxidant known as caffeic acid, may be particularly adept at thwarting the mold's aflatoxin-making mechanisms.

That's according to Bruce C. Campbell, who leads the agency's Plant Mycotoxin Research Unit, and postdoctoral molecular biologist Jong H. Kim. Both are based at the Western Regional Research Center in Albany, Calif.

When the A. flavus mold feeds on certain kinds of tree nuts, the nuts respond by forming compounds called "oxidants." The mold, now undergoing what is known as "oxidative stress," reacts by producing aflatoxin.

However, if the tree nuts' next move is to produce caffeic acid, for instance, this antioxidant can—as its name implies—counter the mold's oxidative stress.

The result? —Caffeic acid can quell nearly all of the mold's aflatoxin production, Campbell and Kim found in their laboratory tests.

This research could lead to safe, Earth-friendly ways to put antioxidants to work in tree nut orchards. For example, antioxidants could be applied to trees, or perhaps the trees' own supply of antioxidants could be bolstered through plant breeding.

The studies are the first to show that oxidative stress that would otherwise trigger or enhance A. flavus aflatoxin production in tree nuts can be stymied by caffeic acid.

An article in the current issue of Agricultural Research magazine describes the investigations.

ARS is the U.S. Department of Agriculture's chief scientific research organization.