Submitted to: Journal of Association of Official Analytical Chemists International
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/1/2007
Publication Date: 11/30/2007
Citation: Park, D.L., Whitaker, T.B., Simonson, J., Morris, H.F., Durr, B., Njapau, H. 2007. Determining the variablity associated with testing shelled corn for aflatoxin using different analytical procedures in Louisiana in 1998. Journal of Association of Official Analytical Chemists International 68(6):1306-1313. Interpretive Summary: Aflatoxin is a naturally occurring toxic and carcinogenic compound produced by fungi and found on many types of grains. The FDA has established a maximum limit for aflatoxin levels in consumer foods and animal feeds. As a result, the grain industry works closely with state and federal regulatory agencies to inspect grain at a buying point in an attempt to detect and remove contaminated grain from the food and feed supply. For both economic and food safety reasons, it is important to use accurate and precise methods to measure aflatoxin in bulk lots sold to elevator operators at the buying point so that lots can be correctly classified as acceptable or unacceptable. The precision associated with the aflatoxin test procedure (sampling, sample preparation, and analysis) used at grain elevators was measured. Sampling was shown to be the largest source of variability in the aflatoxin test procedure. Results indicate that increasing sampling size would be a cost effective method to reduce sampling error. Analytical methods used by elevator operators under field conditions were compared to analytical methods used in state laboratories under controlled conditions. Elevator laboratories tended to measure less aflatoxin than state laboratories. These results indicate that: (1) some contaminated lots above the FDA maximum limit may be making their way into the food and feed supply and (2) elevator operators should review their lab procedures and training methods to improve the accuracy of their analytical methods.
Technical Abstract: The number of elevator facilities with laboratories to test shelled corn for aflatoxin on site is increasing. The inherent difficulty in accurately determining the true aflatoxin concentration of a lot of corn may have serious implications. Deviations from the true value are of even greater significance at busy locations where a high throughput is desired. This study was instituted to (1) measure the differences in aflatoxin test results between elevator laboratories and the Louisiana Agricultural Chemistry (LAC) laboratory and (2) measure the variability in aflatoxin test results, associated with sampling, sample preparation, and analysis of shelled corn at such locations. One hundred lots of shelled corn from 10 elevators in Louisiana were analyzed for aflatoxin using the Aflatest method (at elevators and the LAC laboratory) and high-pressure liquid chromatography (LAC laboratory only). Mean aflatoxin levels determined at elevator laboratories were significantly (p<0.05) lower from those obtained in the LAC laboratory using the Aflatest method. Overall, Aflatest method results were lower than those obtained by HPLC. This difference may be attributed to analyst technical dexterity, difficulty in providing careful attention to detail in a high throughput environment, and/or substandard facilities found at elevators. The total variance was partitioned into the combined sampling plus sub-sampling variance and analytical variance. The sampling and sample preparation steps accounted for about 91.5% of the total variability. When using the HPLC analytical method, the analytical step contributed only 8.5% to the total variance.