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United States Department of Agriculture

Agricultural Research Service


item Whitaker, Thomas
item Trucksess, Mary
item Giesbrecht, Francis
item Slate, Andrew
item Thomas, Frederick

Submitted to: Journal of Association of Official Analytical Chemists International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2003
Publication Date: 8/2/2004
Citation: Whitaker, T.B., Trucksess, M., Giesbrecht, F.G., Slate, A.B., Thomas, F.S. 2004. Evaluation of sampling plans to detect cry9c protein in corn flour and meal. Journal of Association of Official Analytical Chemists International.

Interpretive Summary: StarLink is a genetically modified corn that produces an insecticidal protein. The U.S. Food and Drug Administration (FDA) limits the use of StarLink corn to feed-use only and has established a zero tolerance for StarLink corn in the human food supply. Because some StarLink corn has been found in the food supply, FDA and corn millers now inspect shelled and milled corn destined for human consumption for the presence of StarLink. It is difficult to accurately determine the levels of StarLink corn in large shipments because of the errors associated with the sampling and analytical methods used in the test procedure. Errors in the test procedure result in some lots being misclassified. Some of the good lots test bad and some of the bad lots test good. The sampling and analytical errors associated with measuring StarLink in corn meal and flour was determined. Once the magnitude of the testing errors was known, the effect of sample size and number of analyses on reducing testing errors and the number of lots misclassified was demonstrated. Knowledge of the measurement errors will reduce both health risks to the consumer and economic loss to the processor.

Technical Abstract: StarLink is a genetically modified corn that produces an insecticidal protein, Cry9C. Studies were conducted to determine the variability and Cry9C distribution among sample test results when estimating Cry9C protein in a bulk lot of corn flour and meal. Emphasis was placed on measuring sampling and analytical variances associated with each step of the test procedure used to measure Cry9C in corn flour and meal. Two commercially available enzyme-linked immunosorbent assay kits were used; one for the determination of Cry9C protein concentration and the other for percentage of StarLink seed. The sampling and analytical variances associated with each step of the Cry9C test procedures were determined for flour and meal. Variances were found to be functions of Cry9C concentration and regression equations were developed to describe the relationships. Due to the larger particle size, sampling variability associated with cornmeal was about double that for corn flour. For cornmeal, the sampling variance accounted for 92.6% of the total testing variability. The observed sampling and analytical distributions were compared to the Normal distribution. In almost all comparisons, the null hypothesis that the Cry9C protein values were sampled from a Normal distribution could not be rejected at 95% confidence limits. The Normal distribution and the variance estimates were used to evaluate the performance of several Cry9C protein sampling plans for corn flour and meal. Operating characteristic curves were developed and used to demonstrate the effect of increasing sample size on reducing false positives (seller's risk) and false negatives (buyer's risk).

Last Modified: 05/28/2017
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