North Carolina State University News Services
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Media Contacts:
Dr. Fred Breidt, 919/515-2979
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Tim Lucas, News Services, 919/515-3470
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April 28, 1998
Scientists Use Beneficial Bacteria to Battle Germs on Fresh Produce
FOR IMMEDIATE RELEASE
Even though Americans enjoy the world's safest food supply, highly publicized occurrences of bad hamburger, tainted raspberries and other contaminated foods have shaken public confidence in recent years.
Heat, chemical washes, refrigeration and preservatives are among the most common weapons used to combat the germs that cause these occurrences. But scientists at North Carolina State University are taking a different tack: They're fighting fire with fire, by using beneficial bacteria to stop the growth of harmful bacteria on fresh produce.
"We've found that by treating fresh produce with a small amount of lactic acid bacteria, we can prevent the growth of disease-causing bacteria such as listeria," says Dr. Fred Breidt, a senior researcher in biological and agricultural engineering and food science at NC State.
Lactic acid bacteria (LAB) are microscopic organisms found naturally on many foods, including yogurt and fermented vegetables. "They're nature's own preservatives," says Breidt. "They prevent the growth of other bacteria. And they don't affect food's taste, smell or texture."
LAB previously have been studied for use in improving the safety of meat and dairy products, but Breidt and his colleagues are among only a handful of researchers worldwide investigating LAB's use on fruit and vegetables.
Produce could be treated with LAB in a two-step process, he says. First, chemical treatments or heat would be used to reduce the bacterial population on the produce. Then, a small amount of LAB, cultured earlier from the same type of vegetable or vegetable product, would be re-applied.
The idea is to reintroduce just enough LAB to beat any harmful bacteria that may develop later, without measurably shortening the vegetables' shelf life.Too much bacteria -- even beneficial ones -- will shorten shelf life.
It's a delicate balancing act, complicated by the fact that many different kinds of LAB may be present on vegetables, each with different antibacterial properties and strengths. Identifying which of these will be most effective in inhibiting the growth of harmful bacteria most likely to be found on a specific vegetable, or in a specific food processing environment, is the focus of Breidt's current research.
Working with Dr. Henry Fleming, USDA research leader and professor of food science at NC State, and other researchers in the university's USDA-Agricultural Research Service Food Science Research Unit, Breidt is developing a computer-based mathematical model that weighs various factors to calculate the growth rates and interaction of good and bad bacteria.
"In essence, the model tells us what's going on between the microorganisms; how they battle and inhibit each other, and whether they also inhibit themselves," he says. The model also reveals which external factors -- such as environmental pH or proteinated acids -- play a significant role in bacterial growth. Based on all this data, researchers will be able to choose rationally which LAB is best suited for inhibiting bacteria in a given environment.
In contrast to Breidt's proposed LAB treatment, most food-safety treatments now used on fresh or minimally processed produce rely on refrigeration and washing -- procedures which have been shown to be largely ineffective at reducing bacterial populations.
Breidt and his colleagues also are investigating the use of DNA forensics to evaluate LAB's efficacy as a biocontrol.
Funding for his research comes from a two-year, $86,000 grant from the USDA's National Research Initiative Competitive Grants Program.
-- lucas --
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