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By Shelley Littin
December 15, 2010
Adding oregano to meat before grilling could reduce the formation of potentially cancer-causing compounds by up to 78 percent, University of Arizona researchers have found. The spice also helps inactivate harmful E. coli O157:H7 in the meat.
Research conducted by UA microbiologist Sadhana Ravishankar has shown that a compound in oregano reduces the formation of heterocyclic amines, the potentially cancer-causing culprits that can form in grilled meat.
"We are preventing the formation of potentially carcinogenic compounds in the grilled meat itself, so people can eat safer grilled meat," said Ravishankar, an assistant professor in the UA's department of veterinary science and microbiology in the College of Agriculture and Life Sciences.
Her study was published in the Journal of Agricultural and Food Chemistry.
Heterocyclic amines form in grilled, charbroiled or fried meat in two essential steps. First, a raw juicy hamburger is slapped on the grill. As the meat heats up, amino acids and glucose in the meat react with each other to create molecules known as intermediates. Next, these intermediates react with creatinine, a molecule that is present in muscle. The result is heterocyclic amines.
Once the nice and crispy hamburger is eaten, the heterocyclic amines potentially could lead to cell malfunction. Several epidemiological studies have shown a possible correlation between the consumption of well-done meats and different types of cancers in humans.
So maybe people can live without that extra crispy texture on their meat. Unfortunately that strategy has a pitfall too: There are established standards for cooking ground beef in order to eliminate harmful E. coli bacteria in the vast majority of commercial meat. Restaurants often recommend well-done meat to minimize the potential for foodborne illness.
"The ground beef patty has to be heated to a temperature of 71 degrees Celsius to kill E. coli bacteria," said Ravishankar. "When they say 71 degrees, that means the cold spot at the geometric center of the ground beef patty. What happens is when you're grilling or broiling or frying, it takes longer for the geometric center to reach 71 degrees while the periphery of the meat has already reached that ahead of time and the temperature continues to rise. The higher the temperature, the more the formation of heterocyclic amines."
So it's E. coli on one hand, and potential carcinogens on the other. Not the best of choices. Luckily, a plant compound found in oregano may be a solution to both problems.
"We added the active ingredient of oregano oil, called carvacrol, to the meat. Then we grilled the meat, and we were able to reduce the formation of these compounds," said Ravishankar. "Carvacrol has anti-oxidative properties, so we are thinking that it binds to or reacts with some of the intermediates and prevents them from forming the heterocyclic amines. The mechanism is not clear yet."
Carvacrol also has antimicrobial properties that inactivate E. coli: a membrane-active compound, it breaks the chain of fatty acids that makes up the outer membrane of an E. coli cell, causing the cell to leak its contents.
"We are also hoping that by using these compounds we can reduce the temperature of heating to inactivate E. coli," said Ravishankar. "If you reduce the temperature of heating, you can reduce the formation of heterocyclic amines automatically."
Collaborating with Mendel Friedman at the U.S. Department of Agriculture's Agricultural Research Service Western Regional Research Center in Albany, Calif., Ravishankar is currently testing other anti-oxidative and antimicrobial plant compounds and extracts to find out if they have similar effects as carvacrol on grilled meat.
To prevent compromising the meat flavor and taste, Ravishankar's lab is testing different combinations of plant compounds. "We plan on evaluating different combinations in such a way that you reduce the heterocyclic amines, inactivate E. coli, and at the same time you keep the flavor of the ground beef palatable," said Ravishankar.
In the future, Ravishankar would like to test the effects in animal studies designed to find out whether consumption of meat containing plant compounds helps protect against both infection and cancer.
Meanwhile, Ravishankar's research has shown for the first time a way to simultaneously inactivate harmful E. coli and reduce the formation of potentially carcinogenic compounds in grilled meat itself, hopefully saving us from a future filled with medium-rare food.
This research is funded by a grant from the American Cancer Society through the Arizona Cancer Center.