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After too many uses, commercial frying oil can serve up a cocktail of unpalatable - and potentially dangerous - chemicals. And no regulations exist to help restaurants know how much use is too much. U of G researchers are hoping to change that, thanks to an oil-quality sensor they've developed.
"Generally, restaurants don't know when their oil is of low quality," says Prof. Gauri Mittal, Engineering, who developed the sensor with Prof. Gord Hayward and graduate student Satheesh Paul. "With the sensor, the quality and safety of food will greatly increase."
Before it's heated, frying oil is made up mostly of triglyceride molecules. But when it's used to fry foods at high temperatures - about 160 C to 170 C - thermal changes occur in the oil. It becomes hydrolyzed (hydrogen molecules from steam react with oil chemicals, making new chemicals) and subject to oxidation, which causes chemicals in the oil to react with oxygen molecules in the air. The result is an unhealthy chemistry.
Some of the chemistry's components simply disappear into the air as a gas, but others - such as polymers and free fatty acids - remain and change the oil's chemical composition. These are potentially dangerous to consume, says Mittal. Some are carcinogenic and some damage the liver and kidneys. To make matters worse, old oil is absorbed more readily by food, filling it with even more chemicals.
Many restaurants never completely change their oil, he says. About once a week, when it gets low, they simply add new oil to the existing batch. Some restaurants filter their oil, but this removes only frying sludge. Sometimes, companies are hired to clean frying oil by adding absorbents such as charcoal and silica-based chemicals, then filtering them out, but this step still doesn't rid the oil of all contaminants.
To study the situation more closely, the researchers took oil samples from two restaurants - one in the Guelph area and one in Mississauga. They discovered unhealthy oil in both cases and no method of determining when the oil was bad (oil was deemed "bad" if free fatty acid content was greater than two per cent, polymers were greater than 16 per cent and polar compounds were greater than 25 per cent).
Ultimately, their research led to the development of an oil-quality sensor that uses electrical and optical properties of the oil to measure the levels of chemicals in it. Both an electric current and laser light are passed through the oil to determine its quality. Deterioration is evident when there's an increase in the stored electrical charge and a decrease in light penetration within the oil.
Mittal says the sensor is affordable for virtually any restaurant - between $300 and $1,000.
This research was funded by the Natural Sciences and Engineering Research Council and the Ontario Ministry of Agriculture, Food and Rural Affairs. A U.S. patent was granted in 1999.
When Is Frying Oil Safe?
Canada and the United States lag behind Europe and Japan in regulating frying oil, says Prof. Gauri Mittal, who suggests Ottawa consider the following recommendations. He says oils should be discarded if these are not satisfied:
- Fried foods must taste and appear acceptable.
- All groups of foreign chemicals should not exceed 25 per cent by oil mass.
- The free fatty acid content should not exceed 2.5 per cent.
- The smoke point of the oils should not be lower than 170 C.
- The frying oils should not be heated above 180 C.
Mittal estimates that regulations could be developed for Canada in one year. Exporters of fried food products have contacted him about the oil-quality sensor, anxious to use it to accurately regulate their fried foods and meet stringent export demands.
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