No More Peanut Roulette!
It's a classic word problem in math: You have a jar full of white marbles
plus a blue one, and you're handing out cups full of marbles. What are a
person's chances of getting the blue one?
Let's make it more interesting. Make the "blue marble" a peanut
contaminated with aflatoxina known carcinogen regulated by the Food and
Drug Administration (FDA). Overestimate, and some farmers unfairly lose
profits; underestimate, and some handlers may lose profit or consumers may be
Still want to try and figure this out?
As it turns out, agricultural engineer Thomas B. Whitaker, who is with the
Agricultural Research Service, has made a
career out of developing methods to accurately estimate aflatoxin contamination
in peanut lots so that appropriate handling occurs. His sampling methods have
been relied on by the FDA, USDA, and the peanut industry.
Recent research findings may help both shellers and growers reduce losses
while preserving quality.
When a farmer brings a truckload of peanuts to the buying point, or sheller,
for processing, a grader with USDA's Agricultural Marketing Service takes a
random sample from the load. Another grader looks through a 1-pound peanut
sample for moldy kernels that could possibly indicate contamination from the
aflatoxin-producing Aspergillus flavus fungus.
One moldy kernel is enough to divert an entire truckload to a low-grade
binand to potentially reduced grower profits. Federal price supports are
also linked to this quality assessment.
If a contaminated kernel is found, the load can be re-evaluatedafter
the entire lot is screened to remove foreign material, loose-shelled kernels,
and small pods. But even then, a moldy kernel can condemn the truckload.
Is There a Better Way?
"Shellers have long known that damaged, loose-shelled, or small kernels
are more likely to be contaminated with aflatoxin," says Whitaker.
"Contamination levels in these subgroups bear a statistical relationship
to levels in the entire lot. Shellers just needed an accurate estimate of the
Whitaker determined that ratio: It's five to one. That is, if a sample of
high-risk peanuts from a lot has an aflatoxin contamination level of 100 parts
per billion (ppb), the truckload will probably average 20 ppbthe FDA's
legal limit for food quality safety.
This aflatoxin ratio method might be used to replace or complement visual
analysis. It could uncover some lots possessing more contamination than meets
the eye, while protecting growers from big losses based on one or two unlucky
draws. Measuring aflatoxin in high-risk peanuts provides a more accurate
estimate of aflatoxin contamination than the current visual method.
Whitaker came to his conclusion by taking 2,400 samples from 120 lots. For
each lot, he took five samples and separated them into groups: sound, mature
kernels and sound splits; damaged kernels; loose-shelled kernels; and small
Using a mathematical method known as regression analysis, he developed
prediction models relating aflatoxin from the at-risk product to aflatoxin in
the entire lot.
Some shellers informally experiment with this kind of analysis. But to
establish a standard, the peanut grading service needed something better than
"If the industry decides to formalize this kind of evaluation, they
will already have the mathematical methods needed to ensure they predict
aflatoxin more accurately," says Whitaker. The research was published in
the fall 1998 issue of the Journal of the Association of Official
Analytical Chemists International.By Jill Lee,
formerly with ARS.
This research is part of Integrated Crop Production and Protection
Systems, an ARS National Program described on the World Wide Web at
Thomas B. Whitaker is in the
USDA-ARS Market Quality and
Handling Research Unit, 124 Weaver Hall, Box 7625, Raleigh, NC 27695-7625;
phone (919) 515-6731, fax (919) 515-7760.
"NO MORE PEANUT ROULETTE!" was published in the
July 1999 issue of Agricultural