Fuzz Free is the Way
To Be
A new treatment reduces the number
of potentially harmful pathogens growing on strawberries and increases
the shelflife of the fruit.
Open
up a pint of strawberries from the grocery store, and more often than
not you'll find a fuzzy berry or two in the mix. A blast of chlorine
dioxide gas, however, promises to not only keep those berries
fuzz-free, but also to kill off harmful bacteria living on their
surface more efficiently than methods currently used by the food
industry, say Purdue University researchers.
"Strawberries are
tricky," says Rich Linton, professor of food science and one of the
leaders of the current study on decontaminating strawberries. "They're
notoriously difficult to clean, and their surface composition actually
encourages bugs to grow." Those bugs can include potentially lethal
bacteria, such as E.coli, as well as viruses including
hepatitis A, which caused an outbreak linked to frozen strawberries in
1996.
"The issue with
strawberries is that they're easily contaminated," Linton says.
"They're grown in close association with soil, where they may pick up
pathogens such as E.coli from manure-based fertilizers, and
they're hand-picked, providing another avenue for contamination."
On the Surface
Linton and his colleagues at Purdue's Center for Food Safety
Engineering, who already have demonstrated the efficacy of using
chlorine dioxide gas to kill pathogens on the surface of apples and
green peppers, have shown the treatment also removes significantly
higher levels of pathogens then the current industry-standard
chlorinated water rinse.
Linton's study,
published in the Journal of Food Protection, compares two
different chlorine dioxide treatments, called "batch processing" and
"continuous processing." Both treatments provide greater than a 5-log,
99.999% reduction in the numbers of E. coli and Listeria monocytogenes on strawberry surfaces.
Food safety experts
assess decontamination efficiency with a measurement called "log
reduction", which indicates how much contamination can be reduced
after a decontamination treatment. A log, or logarithm, is a power of
10: thus a 1-log reduction is a 90% reduction; a 2-log is a 99%
reductions, and a 5 log is a 99.999% reduction.
While current methods
for removing pathogens on strawberries yield about a 2.5-log reduction
in bacteria levels, the FDA has stated produce treatments should
achieve a 5-log reduction in pathogens.
Not only does Linton's
treatment significantly reduce the number of potentially harmful
pathogens growing on strawberries, it also extends their shelflife
without sacrificing quality attributes such as color and taste. "The
berries last a lot longer after this treatment. In fact, we've had
strawberries in the refrigerator for more than six weeks with no mold
growth," Linton says.
Both Treatments Work
The two methods Linton used differ in the way the berries are
exposed to the chlorine dioxide. In the batch system, the strawberries
are placed in a sealed container, and a set amount o9f chlorine
dioxide gas is applied once and then allowed to remain in the chamber
for a period of time. Continuous treatment involves constant delivery
of gas in to the chamber over time.
Batch treatment
required higher concentrations of chlorine dioxide treatment for
longer periods of time than continuous treatment, but both methods
achieved more than a 5-log reduction in pathogens, Linton says. He
found that either 30 minutes of batch treatment, or 10 minutes of
continuous treatment, produced effective levels of decontamination.
Linton's team currently
has funding through USDA to scale up this technology and further
develop it for use by the food industry. "We see this technology as a
potential intervention for security applied to our food system,"
Linton says. "It may be possible to develop this technology so that we
can begin decontaminating produce while it's in transit."
