World Grain - May 2013 - 94

MILLINGOPERATIONS

Flour mill
contamination
Prevention, reduction good alternatives
to lessen impact of microbes and bacteria
by Mark Fowler

News reports on foodborne illness and the long awaited publishing of the rules to implement the United State Food and Drug
Administration (FDA) Food Safety Modernization Act (FSMA)
have increased public awareness and concerns about food safety.
Microbial and bacterial contamination of wheat ﬂour has
seldom been a concern due to the fact that it has low water
activity level. Water activity (Aw) refers to the availability of
water in a food or beverage and represents the amount of water that is available to microorganisms. Pure water has an Aw
of 1.00. A water activity level of greater than 0.95 is required
to support the growth of bacteria.
Wheat ﬂour generally has an Aw level of 0.87 or lower depending on ﬂour moisture and temperature. The concern with
wheat ﬂour is that bacteria can be carried or stored and emerge
from dormancy when the ﬂour is further processed into a food
product. In the milling process, prevention and reduction of
microbial or bacterial contamination are good alternatives
with elimination options growing in acceptance, but adding
signiﬁcant cost to production.
PREVENTION
While most of the food safety stories in the media are linked
to E. coli or Salmonella bacteria, Deoxynivalenol (DON),
generally referred to as vomitoxin, is a mycotoxin that may be
produced in wheat kernels. These kernels are usually infected
by Fusarium head blight (FHB) or scab prior to harvest while
in the ﬁeld. The best method to manage DON contamination
is to prevent it from entering the milling process.
To avoid DON contamination, the best practice is to implement quality checks of the incoming wheat and reject supply sources that exceed the safe level. The FDA restriction for
DON in ﬂour is a level less than 1 ppm. The common practice
in the wheat industry is to set the maximum acceptable level
of DON in wheat at 2 ppm.
Quick tests, such as ELISA test kits for DON, are available from several laboratory supply companies, which allow
milling companies to quickly and effectively screen incoming
wheat deliveries. In some situations it is necessary, due to supply or origination constraints, to receive and process wheat in
excess of 2 ppm of DON. In these scenarios, it is possible to
94

remove DON-contaminated wheat kernels during the wheat
cleaning process using gravity tables and optical sorters. This
is not an ideal solution as it concentrates the DON in the wheat
screenings, preventing it from use in animal feed rations and
creates an additional economic loss for the mill.
REDUCTION
Whereas DON-infected wheat kernels can be identiﬁed and
removed in the wheat cleaning process, other forms of microbial contamination cannot be seen. Several treatments of
wheat during the cleaning process are being investigated and
researched to determine their effectiveness in lowering the
microbial load of ﬂour.
One processing method that has proven effective is aggressive scouring or abrasion of the wheat to remove the outer
layers of bran prior to milling. Referred to as debranning or
peeling, this processing step can be added during the wheat
conditioning process.
Drawbacks of using abrasion to remove the bran include
the high amount of energy required to abrade the wheat and
controlling the rate of bran removal. This method cannot
completely remove the bran from the crease of the kernel
which may be the part of the wheat berry most susceptible to
microbial contamination. Debranning also has the drawback
of concentrating the microbial contamination in the bran
portion removed, creating the challenge of how to dispose
or treat the byproduct.
Another method to control bacterial growth being extensively researched is the treatment of tempering water with
ozone or chlorine. Ozone is an unstable and poisonous allotrope of oxygen. It is an effective oxidant widely used as an
industrial air deodorizer, water puriﬁer and in food processing
as a disinfectant.
It has been used in grain storage as a fumigant to control insect infestation. A primary beneﬁt of using ozone is that it is a
natural solution. It degrades into oxygen, leaving no chemical
residue in the grain, ﬂour or processing equipment.
A more common practice in the milling industry is the
treatment of tempering water with chlorine. Chlorination is a
lower-cost solution and more effective method as compared to
May 2013 / World Grain / www.World-Grain.com

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