|Giesbrecht, Francis - NC STATE UNIVERSITY|
|Hagler, JR., Winston - NC STATE UNIVERSITY|
|Young, James - NC STATE UNIVERSITY|
Submitted to: Journal of Association of Official Analytical Chemists International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 9, 2000
Publication Date: September 1, 2000
Citation: JOHANSSON, A.S., WHITAKER, T.B., GIESBRECHT, F.G., HAGLER, JR., W.M., YOUNG, J.H. TESTING SHELLED CORN FOR AFLATOXIN, PART II: MODELING THE OBSERVED DISTRIBUTION OF AFLATOXIN TEST RESULTS. JOURNAL OF ASSOCIATION OF OFFICIAL ANALYTICAL CHEMISTS INTERNATIONAL. 2000. v. 83. p. 1270-1278. Interpretive Summary: Aflatoxin is a carcinogenic and toxic compound produced by molds found in several types of grains. The Food and Drug Administration has established a legal limit that controls the maximum quantity of aflatoxin allowed in food and feed products. As a result, grain products are inspected by processors, manufacturers, and USDA to detect and remove contaminated lots from the food and feed chain. It is difficult to accurately determine the aflatoxin level of large shipments or lots because of the random errors associated with the aflatoxin test procedure. As a result, it is difficult to accurately classify lots according to their aflatoxin content. In order to reduce the number of lots miss-classified by an aflatoxin test procedure, it is important to be able to predict the distribution of repeated aflatoxin test results made on the same lot. A method was developed, using theoretical distributions, to predict the distribution of aflatoxin test results that would be expected when measuring grain lots with a specific aflatoxin test procedure. Researchers need to be able to predict the distribution of aflatoxin test results so that sampling plans can be designed that accurately measure aflatoxin in grain lots. This will reduce both health risks to the consumer and economic loss to the grain industry.
Technical Abstract: Suitability of several theoretical distributions to predict the observed distribution of aflatoxin test results in shelled corn was investigated. Fifteen positively skewed distributions were each fitted to 18 empirical distributions of aflatoxin test results for shelled corn. The compound gamma distribution was selected to model the sample aflatoxin test results for shelled corn. The method of moments technique was chosen to estimate the parameters of the compound gamma distribution. Mathematical expressions were developed to calculate the parameters of the compound gamma distribution for any lot aflatoxin concentration and test procedure. Observed acceptance probabilities were compared to operating characteristic curves predicted from the compound gamma distribution and all 18 observed acceptance probabilities were found to lie within a 95% confidence band. The parameters of compound gamma were used to calculate the fraction of aflatoxin-contaminated kernels in contaminated lots. At 20 ppb, it was estimated that about 6 in 10,000 kernels are contaminated.