Preharvest aflatoxin contamination peanuts

Peanut phytoalexins appear to be involved in resistance to drought-induced preharvest aflatoxin contamination of immature peanuts. Mature peanuts are considerably more resistant to environmentally-induced preharvest aflatoxin contamination of peanuts than are immature peanuts. The mechanism of this latter resistance is unknown. The identification of this resistance mechanism and other resistance may provide one approach to subsequent use of biotechnology to incorporate field resistance traits into commercially acceptable varieties. Biotechnology may also be a valuable approach to exploiting genetic resistance to preharvest aflatoxin found in wild species that have evolved in an arid environment. 

Phytoalexins appear to be at least partly involved in resistance to drought-induced preharvest aflatoxin contamination of peanuts. Phytoalexin-based resistance appears to be more important in immature peanuts than in mature peanuts. Therefore, mature peanuts are more resistant to preharvest aflatoxin contamination than are immature peanuts. The exact mechanism of this resistance is not known. 

The purposes of this chapter are to review the factors involved in aflatoxin contamination of peanuts, review the chemistry of stilbene phytoalexins from peanuts, discuss evidence supporting the involvement of these stilbenes in the bioregulation of aflatoxin contamination, and explore approaches to exploit or enhance such a bioregulative capacity to reduce or eliminate preharvest aflatoxin contamination of peanuts. 

The evidence clearly supports the hypothesis that stilbene phytoalexins in peanuts are an important natural bioregulator of preharvest aflatoxin contamination. That evidence includes the facts that (1) stilbenes are naturally produced in field-damaged peanuts (2) stilbenes possess biological activity against A, flavus and A. parasiticus and (3) although invasion of peanuts by A. flavus and A. parasiticus can occur under any conditions, aflatoxin contamination does not occur until peanuts lose the capacity for phytoalexin production as a result of drought-induced kernel dehydration. 

The goal of our research today is to greatly reduce or eliminate preharvest aflatoxin contamination of peanuts. As the demand for more wholesome food with less risk of exposure to toxins and carcinogens increases, the continued use of peanuts and peanut products as food becomes more dependent on effective management of the aflatoxin problem. 

It is unlikely that any single approach will provide a solution to the problem of preharvest aflatoxin contamination of peanuts. However, a multifaceted approach that could include enhancement of the natural bioregulative properties of stilbene phytoalexins might ultimately yield the solution to a serious and complex problem. 

A considerable amount of research effort has been expended since the discovery of the highly toxic aflatoxins contaminating Brazilian peanut meal in Great Britain in the early 1960 s. Recently some of this effort has been expanded to define the etiology of aflatoxin contamination in peanuts. The preharvest and storage phases of peanut production are most often associated with significant aflatoxin contamination. 

Contamination of peanuts with aflatoxin can occur during various phases of production, storage, handling, and marketing (11). Contamination that occurs after peanuts are harvested is preventable if proper steps are taken to ensure that the moisture of peanuts is maintained at a level that is unfavorable for growth of the af latoxin-producing fungi. However, contamination that occurs in the field prior to harvest (preharvest) is much more difficult to control and usually results in the most severe aflatoxin contamination of peanuts. 

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