World Grain - June 2014 - 108

GRAIN OPERATIONS

can do is be aware and know what your
risk is based on what crop you're testing
and what the weather conditions have
been and your location. You can predict
the risk and direct the testing to that."
Several different types of tests are available from something as simple as a black
light to test for Aspergillus flavus to immunochromatographic assays and High
Performance Liquid Chromatography.
During the testing time, it's important to
minimize the wet holding time, Bowers
said, because mycotoxin levels can increase rapidly in high-moisture grain.
One important factor to remember
is that mycotoxins are not distributed
evenly in grains, and typically occur in
hot spots of contamination.
This may be a result of actual heating
that occurred in a certain area of stored
grain, which promoted fungal spread
and mycotoxin production in that isolated region, Bowers said. It is more
likely due to the localization of grain
harvested from an affected area of the
field in one section of a storage bin.
Aflatoxin is an especially tricky mycotoxin as it takes only a few kernels
to contaminate a lot of grain at an unacceptable level. In the case of corn, it
has been estimated that as few as 6 aflatoxin-contaminated kernels in 10,000

can cause grain to be contaminated at
the regulatory limit of 20 parts per billion. For grain at 15.5% moisture, this
is 6 kernels in approximately six-and-aquarter pounds of grain.
"If you don't detect those accurately,
it can cause problems in categorizing
that grain and putting it in the right market," Bowers said.
The United Nations' Food and Agriculture Organization (FAO) recently released an online tool (www.fstools.org/
mycotoxins/) to help in assessing the
effectiveness of mycotoxin sampling
plans, she said. After entering in sampling specifics, the tool will show the
risk to the seller of being falsely rejected
as well as the risk that a purchaser will
wrongly accept grain that is contaminated above the regulatory limit.
The tool shows that sample size is a
key factor in risk to the buyer. There
is significantly higher risk of wrongly
accepting a lot of contaminated grain
when the sample size is small (about a
pound) compared with a larger sample
size (10 pounds).
"Increasing sample size is one of the
cheapest ways to increase your accuracy in detecting contaminated lots as
long as the sample taken is represenattive of the entire lot," Bowers said.

STORAGE
During storage, drying is a critical
point where contamination can occur.
The more time that passes between
harvesting and drying, the shorter the
allowable storage time for that grain,
Bowers said. Drying too quickly or
at high temperatures can cause stress
cracks in the grain, which are prime entry points for storage fungi.
Strategies like dryeration and combination drying are good options which
reduce the risk for kernel damage that
might promote fungal activity, she
said. Aspergillus and Penicillium fungi,
which produce aflatoxin and ochratoxin,
are the main mycotoxin-producing fungi to be wary of in stored grains as they
can be active at moistures lower than
many other fungi.
Temperature is another important factor during storage. At cool temperatures
(below 60 degrees F), fungi grow very
slowly and many storage insects and
mites are dormant. Aeration can be used
to reduce temperature and minimize
moisture. Maintaining a uniform temperature throughout grain is important
to avoid hot spots of contamination.
Pests can cause kernel damage and
create hot spots, so it's important to control the presence and activity of rodents,

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World Grain - June 2014

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