taminate leafy green vegetables such as spinach and lettuce.
Exposing food such as lettuce or meat to gamma rays or high-energy electrons creates
what are known as free radicals, highly reactive molecules that kill microorganisms by
damaging their genetic material. Hydrogen peroxide works exactly the same way to sterilize
a fresh wound. Within minutes of their formation, free radicals vanish, leaving behind nothing but dead bacteria.
Irradiation does not make foods radioactive, just as an airport luggage scanner does not
make suitcases radioactive. Nor does it cause harmful chemical changes in food. The process may cause a small loss of nutrients, but no more so than with other processing methods
such as cooking, canning, or heat pasteurization.
“Research into the safety of irradiated foods began with the first applications of the tech-
nology back in the 1950s. Throughout the 1950s, ’60s, ’70s, and ’80s, these investigations
used the best tools available, including chemical analysis
and animal feeding studies that lasted for several gen-
erations, and the conclusions drawn by U.S. and inter-
national scientific bodies was that there was no evidence
of any adverse effects of a diet that included irradiated
food. In the 1990s, and even continuing today, the much
more modern tools of cellular and molecular biology
and advanced analytical chemistry have examined irra-
diated foods and have come to the same determination.”
In fact, food irradiation has been used safely and effectively for decades to kill insects and bacteria on imported
spices, and it’s also approved by the U.S. Food and Drug
Administration and regulatory agencies in other countries
to treat meat and poultry. But there’s been some question
as to whether it will work with fresh produce. That’s where
Dr. Niemira’s work comes in to play.
“Currently, I’m researching how effective
irradiation is at killing human pathogens
that are hiding in sheltered spaces between
the cells inside the lettuce leaf as well as
pathogens that are protected within complex
microbial communities called biofilms that
are on the surface of the leaf. Ultimately, I’d
like to know what effect these microscale life
habitats are going to have on our real-world
ability to use irradiation to make food safer.
I’m also working on irradiation treatment of tomatoes and peppers to kill Salmonella, as
these are products for which not much data exists.”
In his research, Dr. Niemira has studied the effects of washing with plain water or a dilute
bleach solution and irradiation on E. coli living deep within the cells of romaine lettuce and
baby spinach. Data from these studies showed that washing, even with bleach, removed or
killed less than 90 percent of the bacteria. Irradiation, however, killed at least 99.9 percent of
the pathogens.
A Food Wrap with a Zap
Of course, food can leave a processing plant free of any pathogens, but still end up contaminated as it winds it way through the food supply chain. But S. D. Worley, a chemist at
Auburn University, may have a solution: a food wrap that incorporates its own disinfectant
within its chemical structure. Dr. Worley described this coating in a recent report in the
ACS journal Biomacromolecules. Here’s how this new polymer film works.
