It can't fly. It doesn't have X-ray vision.
And it certainly can't leap tall buildings in a
single bound.
But when it comes to food safety, the cranberry is a
superhero, according to University of Maine assistant professor and
microbiologist Vivian Chi-Hua Wu, whose research is part of the ongoing
fight to keep humans safe from the menace of food-borne illness.
In Maine, it's natural for researchers in food
science and human nutrition to study the health effects of wild
blueberries. But Vivian Chi-Hua Wu also is one of only a handful of
scientists worldwide studying cranberries from a food-safety standpoint.
Cranberries have long been known for their ability
to fight urinary tract infections and combat the bacterium Helicobacter
pylori that causes certain stomach ulcers. But, as Wu has discovered,
cranberries also have the power to fight food poisoning, eliminating or
inhibiting several important food-borne pathogens.
Wu recently published several studies that show the
preservative and preventative powers of cranberry concentrate. In ground
beef and in the petri dish, the compound slowed the growth of — and in
some cases, reduced to untraceable levels — listeria, salmonella, staph
infection and E. coli 0157:H7, the form of the microorganism responsible
for the 2006 spinach contamination.
Wu, who has ties to both the Maine Wild Blueberry
Commission and the national Cranberry Institute, has found that the
fruits have similar antimicrobial benefits. The difference lies in the
application.
"If you're using cranberry or blueberry as an
antimicrobial preservative compound, in place of a chemical
preservative, you have to study how it will influence the final food
product," Wu says. "Will it change the appearance or the color of a
specialty product? And will that be acceptable? Blueberries have a
darker color, and if you don't want to have a color effect, that's
significant. It really depends on the product you're going to apply it
to."
At her alma mater, Kansas State University, purple ketchup
wouldn't just be acceptable, it would look and taste like team spirit.
Not surprisingly, schoolchildren think a
blueberry-laced burger is pretty neat.
In a sensory study at UMaine, Wu found that
consumers would accept a burger that included up to 5 percent cranberry
or blueberry extract by weight; a mixture of the two berry extracts
scored highest. It looks and tastes like a regular hamburger, but it
fights pathogenic E. coli like a superburger.
Though perhaps best known for her cranberry studies,
they are only one aspect of her groundbreaking work in food safety. Her
collaboration with Chih-Sheng Lin of National Chiao Tung University in
Taiwan caused quite a stir at the 2008 Institute of Food Technologists
conference. The two researchers have found a way to detect pathogenic E.
coli in food with the naked eye, using nanotechnology.
Because the industry has a zero-tolerance policy for
E. coli O157:H7, meat suppliers routinely examine their products to
detect the bacteria using USDA microbiological examination methods.
These methods are considered the gold standard, but it takes a long time
to get results.
The quick, easy and affordable method developed by
Wu and her colleagues could allow consumers and producers to know
immediately whether their food is safe to eat, because the presence of
pathogenic E. coli causes the nanoparticles to change color. The
implications for the industry are revolutionary.
"There's potential to develop something very simple,
maybe even something a consumer could use — as simple as a strip of
paper that you dip into your food. If you see the right color, you know
your food is safe," she says.
A bit less simple but equally impressive are the biosensors Wu
and her colleagues developed. One DNA strand, which recognizes a target
pathogen, is placed on a tiny chip. If the same pathogen is present in,
say, a package of meat, the chip will attract other DNA strands, causing
a minute shift in mass. This shift in mass translates into a change in
frequency emitted by the chip, which can be easily read by a computer.
In other words, a quick scan of the chip will detect contaminants.
Wu's also keeping an eye on potential food-safety
threats hidden in plain view. Common pathogen detection methods will
find harmful bacteria. But if a bacterium has been injured — not killed
— during processing, it could repair itself.
"If you use the common method to verify whether you
have any organisms left after treatment, this will tell you there's
nothing left, but it actually missed a group called injured
microorganisms," Wu says. "(When food containing injured bacteria is
consumed) our human body provides a very, very nutritious environment to
let injured microorganisms recover, and once they recover, they start
activating harmful bacteria."
Wu has not only identified the threat, she has found
a way to keep it under control. The detection methods she developed in
2003 and 2006 are the industry standard, and she still receives phone
calls and e-mails about them.
"I think there are a lot of natural things we can
look into," says Wu, talking about the potential for cranberries and
blueberries to keep food-borne illnesses at bay. "By preventing these
pathogens, you can provide safer food products."
by Kristen Andresen
January - February, 2009
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