Submitted to: Book Chapter
Publication Type: Book / chapter
Publication Acceptance Date: 10/20/2004
Publication Date: 12/10/2005
Citation: Campbell, B.C., Molyneux, R.J., Schatzki, T.F. 2005. Advances in reducing aflatoxin contamination of u.s. tree nuts. In: Abbey, H., editor. Aflatoxin and Food Safety. Boca Raton, FL:CRC Press. p. 483-515. Interpretive Summary: A collaborative team of scientists at the USDA's Western Regional Research Center and the University of California have been researching ways to reduce aflatoxin contamination of food commodities, mainly tree nuts. Aflatoxins are chemicals made by a group of opportunistic fungi that are commonly found in agricultural settings. Aflatoxins are also carcinogenic. Very low tolerance levels have been set by the FDA and international agencies for the presence of aflatoxins in food products. These low tolerance levels have particularly affected tree nuts since almost 50 to 70 % of domestic production are exported. Through their research efforts, the scientific team has developed a number of tangible products and methods to reduce aflatoxin contamination. These efforts have resulted in the following: 1) a lure to control a major insect pest, 2) breeding tree nuts resistant to fungal attack, 3) improving management of tree nut orchards to reduce fungal populations, 4) improving sampling for aflatoxin contamination, 5) developing an automated sorter that removes aflatoxin-contaminated nuts during processing, 6) discovery that overseas hand-cracking of un-open pistachio shells increases the risk of aflatoxin contamination, and 7) the most important discovery, a natural chemical in walnuts that inhibits the ability of fungi to make aflatoxin.
Technical Abstract: Aflatoxins are carcinogenic to humans and farm animals. Certain species of Aspergillus synthesize aflatoxins are common to agricultural environments. Aflatoxin contamination is a food safety concern affecting corn, peanuts, cottonseed, and tree nuts (almonds, pistachios and walnuts). Commercial production of tree nuts in the U. S. is entirely in California wherein 50 to 75% of production is exported. Scientists at the USDA's Western Regional Research Center and the University of California, Davis have developed products and methods to reduce aflatoxin contamination of tree nuts. These developments include: 1) Discovery of a potent lure to control codling moth, whose feeding damage leads to infection by A. flavus; 2) Breeding and genetic engineering of new varieties of almonds and walnuts resistant to insect attack, 3) Developing management strategies to reduce reservoirs of A. flavus in tree nut orchards; 3) Discovery of saprophytic yeasts which show promise as biological control agents of A. flavus; 4) Improving risk assessment models for sampling and measuring aflatoxin contamination; 5) Developing an automated sorter that removes aflatoxin contaminated nuts from processing streams; 6) Discovery that current methods for hand-cracking closed shell pistachios can result in a higher aflatoxin contamination, and; 7) The foremost breakthrough, discovery of a potent inhibitor of aflatoxin biosynthesis, rendering aflatoxigenic A. flavus atoxigenic.