Natural Products: The Promise of Peanut Shells, the Value of Violets

by Horace G. Cutler, Research Leader and Coordinator, Microbial Products Research Unit, Russell Agricultural Research Center, ARS, USDA, Athens, GA.

Around the world, many people are vitally concerned about protecting the environment while maintaining a sustained agricultural and industrial base. Both goals can be met by treating ordinary, everyday objects and substances to create safe agricultural chemicals, pharmaceuticals, flavors, and other commercial products.

Plants found in nature contain many compounds, and some of those compounds may serve as natural pesticides if resources are dedicated to their development.

In their intensive efforts to keep a steady, safe, and inexpensive supply of food and fiber available to the public, USDA scientists and others are finding agricultural chemicals that are safe for both the environment and people. These chemicals are an integral part of nature and are readily biodegraded.

Pressure To Produce

As the human population increases, resources become more strained in coping with conflicting needs for land use. Demands for food production, housing, and recreational areas (for hunting, fishing, camping, and hiking) reflect the sometimes differing values of various groups the environmental, industrial, and agricultural interests.

After World War II, the productivity of the American farmer became the envy of the world. Never before had such a cornucopia been produced by so few. This productivity was based on three factors: canny farmers who knew their business, superior farm machinery, and pesticides (including herbicides, insecticides, fungicides, rodenticides, cotton defoliants, and plant-growth regulators).

In 1962, Rachael Carson's Silent Spring was published, and the widespread use of pesticides was questioned for the first time. The greatest insecticide in the history of the world, DDT, had become highly suspect because (among other things) it caused thin and brittle eggshells in birds. It was discovered that DDT had leached from the fields into the streams and rivers and had been ingested by fish.

The birds ate the fish and also the insects that had been poisoned by the insecticide, and the ecological cycle was again almost complete.

But some of us will remember the benefits of DDT during and after World War II. Refugees moving across war-ravaged Europe were stopped at checkpoints and dusted with DDT to kill lice and fleas, because fleas can carry bubonic plague (which still exists on the North American continent). In 1959, yellow fever and malaria in Trinidad, West Indies, had just been eradicated by the control of the carrier mosquito. My wife and I were living there at the time, and we found our luncheons regularly disturbed by a man with a sprayer full of DDT. He would announce in his best Trinidadian, "We commin' in, mun! and then thoroughly spray the inside of the house. To refuse him entry would have resulted in a hefty fine and jail sentence. If the entire island had refused the pesticide spray program, yellow fever and malaria might not have been eradicated.

But we cannot go back to things as they were. The world today is very concerned about agricultural pollution in all forms, especially pollution caused by the use of pesticides. The Green Movement in Europe, the various ecological organizations in the United States, the watchdog agencies, and even the filmmakers have strong opinions about the use of pesticides and the results of their residues on land and in food crops. Sometimes the criticism is absolutely correct and sometimes it is a little distorted. All sorts of facts, figures, and extrapolated data come into the discussions. But one thing is certain: Because of registration costs, many of the agricultural chemicals presently on the market will eventually be withdrawn by chemical companies. It is quite possible that during the next 5 years many, if not all, of the fungicides in use today will no longer be available. Although many of the synthetic agricultural chemicals do not pose a hazard, the question of their persistence in the soil or in food commodities is of paramount importance to the public welfare.

Can we grow crops without the use of chemicals? The answer is mixed. It may be possible to grow pesticide-free crops (organically grown) in specific environments on a small scale, but it is almost impossible to do so on a large scale in humid semitropical areas (such as Southeastern United States) and in the Tropics. The incidence of weeds, insects, and disease seems to explode in warm climates.

The Promise of Natural Products

A middle ground between concentration on synthetic pesticides and use of none at all involves the use of natural products that possess biological activity. These natural products are organic compounds that nature regularly sees, recognizes, and handles by taking them apart easily. They are derived from plants, micro-organisms (fungi and bacteria), and insects and can be used as agrichemicals. Their characteristics are as follows:

1. They have very high specific activity so that only fractions of an ounce are used per acre.

2. They are target-specific and are not broad spectrum (that is, nontarget life is unaffected).

3. They are biodegradable and do not persist in the environment.

4. Some may be transformed in biological systems (by refermentation) to give new biologically active compounds with different activities.

5. Some are both agrochemicals and pharmaceuticals.

6. They come from highly renewable resources. Certain plants may be new high-cash crops for rural areas.

An intensive search is under way by USDA's Agricultural Research Service (ARS) to discover natural products for utilitarian use. In one project, USDA-ARS scientists are developing an inexpensive product from peanut shells, called Gostar (patent pending). This is primarily intended to produce, by the fermentation of a Penicillium (fungus), a natural product having both antitumor properties (for use as a pharmaceutical) and plant growth regulating properties (for use as an agrochemical). The goal is to produce large quantities inexpensively.

Gostar is now being used to inexpensively make a compound called 6-pentyl-o-pyrone (PAP) from the fungus Trichoderma. In its relatively pure state, PAP kills fungi that attack fruit trees and also other objectionable fungi in stored food products. The latter include such organisms as Aspergillus flavus, which produces aflatoxins that are potent inducers of liver cancer. Obviously, a nontoxic fungicide would be very useful in eliminating this problem, especially because (as stated earlier) most of the presently available fungicides may be removed from the market. PAP, which has also been found in the natural essence of peaches, was originally produced on a small scale for use as flavoring in baked goods; it has a buttery, cakelike flavor, and has been fed to humans on taste panels.

Violets Versus Fungi

A second example of a natural product being sought for utilitarian use relates to flowers. In the play and movie My Fair Lady, Eliza Doolittle, the flower vendor in Covent Garden, sold Devonshire violets. These English violets look identical to their American cousins; both are deep purple. But the English violet differs in that it grows in a cool, moist climate and it exudes a pleasant, penetrating perfume. The perfume, a natural product, is B-ionone.

ARS scientists have developed a process that can use peanut shells to produce a natural product with pharmaceutical and agrochemical properties. Jack Dykinga/USDA 91BW1970-36

Some years ago in midsummer in southern Georgia (in the United States), when the temperature was 95 F and the humidity was also high, I wandered into the laboratory of a chemist colleague. Without thinking, I exclaimed, "Where did you get the English violets?"

Then I recovered and said, "That's a silly question; it's too hot, and they don't grow in the South. In fact, I don't know of any scented violet in the States."

My colleague told me that he had the violets because he was working with B-ionone (a compound used in the perfume industry worldwide) in conjunction with another scientist because the natural product has antifungal properties. That work led to a joint patent by USDA-ARS and the University of Georgia for the use of B-ionone as a fungistatic agent.

These and other natural materials not only can be safe for the environment but also can have international use as agrochemicals and pharmaceuticals, thus promising a profitable presence for the United States in the global marketplace.