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The Mighty Cranberry

Illustration by Carol Nichols

The Mighty Cranberry


Out of the Blue
Vivian Chi-Hua Wu has worked with the Maine Wild Blueberry Commission to develop an affordable, efficient method to combat microorganisms on fresh fruit.

Vivian Wu
Vivian Wu

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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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