Quick Facts...
- Aflatoxin and other mycotoxins are heat-stable toxins produced by
fungi.
- Aflatoxins and other mycotoxins have not been shown to be a
problem in the field, but after harvest they may form in corn
during storage.
- These toxins can be a serious problem in grain stored under
unfavorable conditions.
- Black light screening is not a conclusive test for aflatoxin.
- Positive tests indicating aflatoxin must be confirmed by chemical
analysis.
Aflatoxin, a toxic metabolic by-product of certain fungi, is a threat
to the safe use of corn products as food for humans and livestock. National
news accounts generally quote that the Midwest to Southeast areas of the
United States may experience serious problems with aflatoxin in corn.
Very little attention is directed to the far West. Dangerous levels of
aflatoxin seldom occur in Colorado corn fields when dry cool fall harvest
conditions prevail or proper storage conditions are used. When necessary,
corn is tested for aflatoxin prior to use.
The fungi (mold) that produce aflatoxins can infect
important food and feed Crops before, during and after harvest.
These fungi, especially Aspergillus flavus and A. parasiticus,
are normal soil-borne inhabitants in our environment, growing on
both living and decaying plant matter. The major products in
which aflatoxins are produced include corn grain, soybeans, dry
beans, cottonseed, grain sorghum, wheat, peanuts and tree seeds.
Mycotoxins include metabolic by-products produced by a
number of different fungi that may or may not be toxic. One of
the mycotoxins, aflatoxin, is produced by the fungi Aspergillus
flavus and A. parasiticus. Four different aflatoxins, B1, B2, G1
and G2, have been identified with B1 being the most toxic,
carcinogenic and prevalent.
Another important family of toxin producers is Fusarium. The toxins
zearalenone, trichothecenes or moniliformin can be formed by F. moniliforme,
F. oxysporum, F. culmorum, F. avenaceum, F.
equiseti, F. roseum, and F. nivale. Scientists
do not yet know how many mycotoxins exist even though more than 250 have
been detected.
Growth, Detection and Testing
Three conditions that favor continued mold growth are necessary for
aflatoxin formation. They are: high corn kernel moisture (16 to 30 percent);
warm temperatures (77 to 90 degrees F); and high humidity (80 to 100 percent).
Corn exhibiting mold formation doesn't necessarily contain
aflatoxin. Growth of the fungus is poor at temperatures below 50
degrees F but slow growth will occur and low amounts of aflatoxin
may be produced under favorable moisture conditions. Moisture
levels below 12 to 13 percent will prevent mold formation.
The Bright Greenish Yellow test (BGY) with black light (365 nm) commonly is
used as a screening device to detect only aflatoxins in corn. Proper use
of the BGY fluorescence test is only a presumptive test for the
presence of toxin. A BGY reference standard can be obtained from Dr. Odette
Shotwell, Northern Regional Research Laboratory, Peoria, Illinois, 61604.
The BGY fluorescence is not emitted by the aflatoxin itself but from kojic
acid, a compound produced by A. flavus at the same time aflatoxin
is produced. The black light method is no longer used by the Federal Grain
Inspection Service because of the high probability of false positives
and negatives. Chemical analyses are required to confirm the presence
and level of aflatoxin contamination.
Sampling
- Collect a 10-pound sample by taking a minimum of five random
probes throughout the grain lot.
- Crack the entire sample coarsely and examine under long-wave
ultraviolet light (365nm) for BGY inflorescence. A reference
standard is essential for the untrained technician.
- BGY florescence found in the cracked sample is a preliminary
test and does not prove that corn is contaminated.
Action Levels For Aflatoxin in Corn Grain
The Food and Drug Administration (FDA) Center for Veterinary
Medicine (CVM) and the Center for Food Safety and Applied
Nutrition (CFSAN) have established the following aflatoxin
"action" levels. The CVM and CFSAN prohibit aflatoxin
contaminated corn being shipped in interstate commerce when:
- Corn containing in excess of 20 parts per billion (ppb)
aflatoxin is intended for consumption by humans, immature animals
(including immature poultry) and dairy animals, or grain sent to
an unknown destination.
- Corn containing in excess of 100 ppb aflatoxins for
consumption by breeding cattle, breeding swine, or mature
poultry.
- Corn containing in excess of 200 ppb aflatoxins for feed to
finish swine (e.g., 100 lbs or greater).
- Corn in excess of 300 ppb aflatoxins as feed destined for
finishing (i.e., feedlot cattle).
The Agricultural Stabilization and Conservation Service
(ASCS) states that corn with aflatoxin levels above 20 ppb is
ineligible for crop loans. Growers can receive disaster
assistance payments if they agree to destroy contaminated grain.
Any blending of affected corn must be approved by FDA.
CFSAN prohibits the sale of milk or milk products in
interstate commerce that contain more than 0.5 ppb aflatoxin
residue. Research indicates that 0.5 ppb aflatoxin level in milk
normally would not be exceeded if the cattle feed contains less
than 20 ppb aflatoxin. Toxins fed to dairy cows can be
metabolized to aflatoxin M-1 by the liver and secreted in milk.
Animal Symptoms
Losses due to aflatoxin contamination occur at all levels in
production, marketing and use, and cause losses to
growers, elevators, manufacturers and livestock feeders. Extreme
toxicity has been known to cause poultry losses and reduced
cattle, sheep and hog gains. Losses usually are expressed as
reduced grain quality for market.
Diseases produced by mycotoxins are known as mycotoxicoses.
There are numerous mold toxins identified. Fungi capable of
producing mycotoxins include Aspergillus, Fusarium, Penicillium
and other common contaminants of stored grain. The following are
symptoms from ingestion of contaminated feed for specific
animals.
- Poultry: reduced growth rate, decreased resistance to
infection, fatty liver syndrome, death.
- Swine: decreased feed efficiency, reduced rate of gain,
stunted growth, suppressed immune system.
- Cattle: reduced feed intake, reduced rate of gain, reduced
feed efficiency and reduced reproductive performance.
- Dairy: decreased milk production, conversion to aflatoxin M-1
that is secreted in the milk.
If a toxic level of aflatoxin is eaten, replace contaminated
feed with good feed and call a veterinarian.
Safe Storage
Safe storage of grain requires dry, cool conditions inside
the bin. Bins filled in the fall tend to have grain moisture
levels between 15 and 18 percent moisture with lower percent
moisture preferred. Average grain temperatures should be
maintained within 10 degrees F of outside surrounding temperatures. Rapid temperature changes and moderate moisture reduction is accomplished by using adequate aeration.
Follow these guidelines for safe storage:
- Thoroughly clean grain bins before storage. Remove all dust,
dirt, crop debris, chaff, and cracked, broken and contaminated
kernels that would interfere with adequate ventilation.
- Harvest as soon as the moisture content is low enough for
safe storage.
- Store corn safely at 15 percent moisture until spring but to
13 percent for storage of one year or more. Grain temperatures
must be reduced where possible, to 35 to 40 degrees F for winter
storage.
- Intermittent bin aeration at 0.5 cfm/bu is recommended to
prevent moisture migration within the bin.
- Monitor grain moisture and temperature every one to four
weeks to detect "hot" spots, musty odors and unusual moisture
accumulations.
- Have any moldy "suspect" grain chemically tested for toxins
by a reputable laboratory.
References
- Croissant R. L. 1992. Managing stored grain, fact sheet
0.117. Colorado State University Extension.
- Doupnik B. 1983. Aflatoxins in Corn - background and proper use
of black light. Nebguide G83-644. Extension Service University
of Nebraska. Lincoln NE.
- Hermann, Tim. 2002. Mycotoxins in Feed Grains and Ingredients. Kansas
State University Agricultural Experiment Station and Extension,
MF-206.
- Stack J. and Carlson M. 2003. Aspergillus flavus and Aflatoxins in
Corn. NebFacts NF 03-571. University of Nebraska Extension Service,
Lincoln, NE.
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