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Cooking Process Reduces
Toxin in Corn
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A Guatemalan woman shells
corn for tortillas. Corn
products in her country are
sometimes made from low-
quality corn that is high
in fumonisins, compounds
known to cause sickness
and cancer in animals.
(K9554-17)
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If you stare at the word
"nixtamalized" long enough, you can almost see the word
"tamale." That's so apropos because many Mexican and Central American
corn products—tamales, masa flour, and tortillas—are made by a
high-temperature, alkaline cooking procedure called nixtamalization.
In some developing countries, corn is of a lower quality than in the United
States, and that presents an emerging health concern for residents of Central
America and Mexico, where corn is a major dietary staple.
Low-quality corn may contain high levels of fumonisins, pronounced
few-MON-i-sins. These toxins are produced by the fungus Fusarium
verticillioides (synonym F. moniliforme). Although no definite harm
to human health from fumonisins has been determined, they cause sickness in
horses and pigs and cancer in laboratory rats. |
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Many corn products such as
tortillas and tortilla chips
are made using a cooking process
called nixtamalization, which
can reduce fumonisin levels in raw
corn by nearly 80 percent.
(K9555-10)
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Before assessing the risk of
fumonisins in corn products made in Guatemala, pharmacologist Ronald T. Riley,
who is in the ARS Toxicology and
Mycotoxin Research Unit, Athens, Georgia, surveyed the dietary habits of
residents in two rural villages in that country's Central Highlands: Patzicia
and Santa Maria de Jesus. He discovered that men ate, on average, more than a
pound of corn tortillas daily, and women consumed about 14 ounces. By
comparison, a survey of North American adults revealed daily tortilla
consumption of 0.12 ounces per day.
In 1995, Riley and ARS chemist Filmore I. Meredith began investigating
corn-processing methods in Guatemala. The study was a collaborative effort of
ARS, Emory University, and the Instituto de Nutrición de Centro
América y Panamá (INCAP). Current studies are supported by USDA's
Foreign Agricultural Service, the Agricultural Research Service, and the
International Life Sciences Institute of North America.When Riley's study was
begun, INCAP researchers didn't have the ability to analyze corn for
fumonisins. Now, with USDA assistance, INCAP researchers will develop those
skills. |
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Chemist Mary Ann Dombrink-
Kurtzman examines corn that
has been cooked in a
solution of water and lime,
the first step in nixtamalization.
(K9554-6)
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In Guatemala, corn is harvested,
dried, and graded as being clean, spoiled, or rotten based on the amount of
fungal and insect damage. Then it's bagged for storage. Kernels are removed
from the cob and mixed in a ratio of one-third clean, one-third spoiled, and
one-third rotten. This mix is added to near-boiling water treated with lime.
When the corn is soft enough, the liquid is poured off and the remaining
material is a hominy-like slurry that is called nixtamal. The nixtamal is then
rinsed with water—if it is available.
"How much they rinse is critical because water washes out some of the
toxins," says Riley. At the time of the study, water supply in Santa Maria
de Jesus was erratic, making the washing process difficult.
"We found that nixtamal from Santa Maria de Jesus had higher levels of
fumonisin B1 than nixtamal in Patzicia," he says. |
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In the Central
Highlands of
Guatemala, corn
is graded as
clean, spoiled,
or rotten, then
combined before
it is made into
tortillas. This
ear was rated
rotten.
(K9554-18)
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Nixtamal from Santa Maria
de Jesus contained an average of 14 parts per million of hydrolyzed fumonisin
B1, a chemically converted product of fumonisin B. There was
a much higher level of hydrolyzed fumonisin B1 in the cooked
tortillas from Santa Maria de Jesus (26 parts per million) than in tortillas
made in Patzicia (6 parts per million).
"These high levels of fumonisins in the tortillas indicate that the
quality of the corn used was very low," says Riley. More rinsing may have
further reduced the toxin content of the tortillas. "It's also possible
that the more affluent community of Patzicia used higher quality corn for
preparing tortillas," he says.
In the United States
In related research, ARS chemist Mary Ann Dombrink-Kurtzman in Peoria,
Illinois, and ARS pharmacologist Kenneth A. Voss in Athens, Georgia, are also
studying nixtamalization. Dombrink-Kurtzman conducted one of the first
analytical studies of fumonisins during all phases of nixtamalization. This
analysis is important because the population of immigrant citizens of Central
and South America is growing in the United States and so is interest in their
foods, she says.
"Though U.S. corn destined for human consumption normally contains low
levels of fumonisins, drought stress in some years can raise the levels,"
says Dombrink-Kurtzman. She works at the National Center for Agricultural
Utilization Research, where she investigated the fate of fumonisins during the
production of masa and tortillas. She first searched the United States for
normal-appearing contaminated corn—a search that took almost a year. The
processing was performed in collaboration with Lloyd W. Rooney, a professor at
Texas A&M University in College Station, Texas.
After examining samples from laboratory-made tortillas, Dombrink-Kurtzman found
that "nixtamalizing corn to make tortillas reduces the level of fumonisins
in raw corn by nearly 80 percent."
Over the last 3 years, the corn milling industry has voluntarily screened about
2,000 cornmeal samples. "Based on their data of low fumonisin levels and
combined with the fact that nixtamalizing further reduces fumonisins, U.S. corn
tortillas might be expected to contain between 0.02 and 0.2 parts per
million," Dombrink-Kurtzman says.
According to Voss, who works at the Russell Research Center in Athens, Georgia,
"We found similar reductions in fumonisins in fried tortilla chips
prepared on a pilot production line." The work was part of a research
agreement between ARS and Frito Lay, Inc.—By
Sharon
Durham, and Linda McGraw,
Agricultural Research Service Information Staff.
This research is part of Food Safety, an ARS National Program (#108)
described on the World Wide Web at http://www.nps.ars.usda.gov.
Ronald T. Riley,
Filmore I. Meredith, and
Kenneth A. Voss are in the USDA-ARS
Toxicology and
Mycotoxin Research Unit, 950 College Station Rd., Athens, GA 30604; phone
(706) 546-3377 (Riley), (706) 546-3405 (Meredith), (706) 546-3315 (Voss), fax
(706) 546-3116.
Mary Ann Dombrink-Kurtzman
is in the USDA-ARS Mycotoxin
Research Unit, National Center for Agricultural Utilization Research,
1815 N. University St., Peoria, IL 61604; phone (309) 681-6254, fax
(309) 681-6686.
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"Cooking Process Reduces Toxin in Corn"
was published in the August 2001
issue of Agricultural Research magazine.
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