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Safer Cooking

Olive Oil, Lower Temperatures Less Toxic in Frying

Frying with canola oil releases more toxic fumes into the air than frying with olive oil, according to a new study conducted at the University of Dayton Research Institute. And frying at temperatures higher than 350 F, a common practice in American kitchens, releases higher levels of toxins --significantly higher levels from canola oil --than frying at the recommended 350 degrees.

As a result, researchers are recommending frying with olive oil whenever possible and adhering to the 350-degree frying temperature recommended by the International Olive Oil Council.

During a three-month visit to the University of Dayton Research Institute, Angel Carbonell Barrachina --a  professor of food technology at Universitas Miguel Hernandez in Orihuela, Spain --worked with UDRI researcher Sukh Sidhu and visiting Fulbright Scholar Andres Fullana to collect and analyze emissions from canola oil and two types of olive oil --extra virgin and "lampante" virgin. Lampante, locally known as "regular" olive oil, is chemically processed to remove most flavors from the oil and is typically the most inexpensive of the virgin oils. It's often the choice of chefs who appreciate the health benefits of olive oil, but don't care for the strong taste of extra virgin oil, Carbonell said.

The researchers focused on emissions of volatile pollutants, particularly the chemical compounds acetaldehyde and acrolein --both the subject of pollution studies by the EPA. The EPA has declared acetaldehyde a "probable human carcinogen" and acrolein "extremely toxic to humans" and "a possible human carcinogen." (From the "National Air Toxics Program: The Integrated Urban Strategy Report to Congress," 2000.) They cooked the oils for 15 hours at 180 degrees Celsius (or 356 F), and for seven hours at 240 degrees Celsius (or 464 F).

At 180 C, canola oil released twice the amount of acetaldehyde as extra virgin olive oil and as much as four times the levels of acetaldehyde emitted from regular olive oil. Acrolein levels emitted at this temperature were five and one-half times higher than from either of the olive oils.

At 240 C, canola oil released two and one-half times the amount of acetaldehyde as extra virgin olive oil and as much as five times the levels of acetaldehyde emitted from regular olive oil. Acrolein levels emitted at this temperature were as much as nine times higher than from either of the olive oils.

"Those are significant differences, especially at the higher temperature," Carbonell said. "A lot of people fry at the higher temperature, especially when they stir fry. What's important about this research is that we're not talking about toxins being absorbed into the body by ingestion but by breathing them. So they can be harmful to the person who is cooking and others nearby."

Although the researchers used deep-frying techniques to test the oil, Sidhu --a senior research scientist in UDRI's energy and environmental engineering division --said the emissions are just as harmful when using lesser amounts of oil, such as when cooking in a wok. In fact, the UDRI study was prompted by other studies released in the last decade that indicate the air in homes in China is often significantly more polluted than the air outside. Those studies also attribute toxins from burning coal and cooking oil to greatly increased rates of lung cancer in women in some areas of China.

Because of the common practice of cooking with olive oils in Mediterranean countries as well, Carbonell wanted to investigate the toxic properties of fumes from those oils in cooking.

"What really surprised us was that there was relatively little difference in the levels of emissions from the two olive oils, either the extra virgin or the plain," Carbonell said. "And olive oil is actually healthier than canola and other oils." The researchers theorize that the inherent antioxidant qualities of olives oils may have prevented fatty acids from breaking down and releasing toxins as quickly as canola oil.

Based on the research, Sidhu and Carbonell recommend using olive oil when frying. "It's also very important not to fry oils at temperatures hotter than the recommended temperature of 350 F," Sidhu said.

Carbonell, who visited UDRI through a summer faculty research fellowship funded by the Spanish Ministry of Education, said he plans to return to UDRI for additional studies on other types of oils and how different foods might affect emissions. "We're also planning to study whether adding antioxidants to oils inhibits the breakdown of fatty acids and release of toxins as they do in olive oils," Carbonell said.

Fullana, who just completed his first year of a two-year appointment at UDRI to study how pollution effects the food chain in his homeland of Alicante, Spain, helped conduct the cooking oil research. He and Carbonell specifically requested to conduct their research at UDRI. "Only about 10 research programs for heat and emissions exist in the world, and UDRI has one of the best," Fullana said.

For media interviews, contact Sukh Sidhu at (937) 229-2846.

September 25, 2003


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