Many food items are fried in the home, ranging from meat, fish, plantain, chips, yam to pastries such as puff-puff and buns. Frying, a common method of cooking dates into ages and it is the preferred method with some people because of the added flavour and the attractive appearance.
Frying has fallen into some disfavour in recent years, with everyone watching his or her fat intake and cholesterol count. Now, experts have also warned against the potential danger of re-heating cooking oil for multiple uses.
Experts said that at frying temperature, aside the fact cooking oil releases toxic compounds (aldehydes) that pollute the atmosphere and can be inhaled, some of these toxins also remain in the oil that was heated and reheated. And so, foods that are fried in such cooking oil subsequently will absorb these toxins. These are toxic compounds linked with brain diseases and some types of cancer.
Certain cooking oils undergo significant degradation of their fatty acid contents when they are heated and reheated. And while some of these aldehydes dissipate after being produced in cooked oil, many others linger and accumulate. That is why they can be found in cooked food. Upon consumption, these toxins then react with human proteins, enzymes and hormones, which can lead to serious health problems.
Cooking oil is fat that is used for cooking and is usually liquid at room temperature. Some saturated oils such as coconut oil and palm oil are more solid at room temperature than others. Cooking oil may be of plant or animal origin.
The research, published in the journal of Food Chemistry, involved heating three types of oil (olive, sunflower and flax seeds) in an industrial deep fryer at 190 degrees Celsius. This was carried out for 40 hours, eight hours a day in the first two, and 20 hours for the linseed oil.
Using gas chromatography / mass spectrometry analysis procedures, they discovered that sunflower oil was the worst offender for toxic aldehydes, followed by flaxseed oil, also known as linseed oil, and olive oil. And the more times these oils were reheated, the worse their concentrations of toxic aldehydes became.
Similarly, a study at the University of Minnesota’s Department of Food Science and Nutrition, found that soybean oil produces similar concentrations of other toxic aldehydes when fried at a temperature of 185 degrees Celsius (365 degrees Fahrenheit).
Mr Tunde Ajobo, a dietician, at the University College Hospital (UCH), Ibadan, Oyo State stated that individuals should never heat oils to the smoking point, as this not only damages their fatty acid content, but also their taste.
According to him, “from the point of view of nutrition, initially when one cooks with oil, the nutrients in the oil, such as omega 3 fatty acid, is absorbed by the food. But with subsequent heating, the minerals and vitamins it might contain would have being exhausted.
Oils that are healthy at room temperature can become unhealthy when heated above certain temperatures. Whether refined or not, all oils are sensitive to heat, light, and exposure to oxygen.
Mr Ajobo remarked that re-use of cooking oil was a habit that should be discouraged because most of such, oils are usually poorly stored and as such could easily go rancid, adding “once any oil is heated above the flash point, its composition is changed. The oil may contain other substances that are unknown to the body which can wreak havoc to the body system and affect the health of man.”
The expert declared: “Of course, some people wait till this flash point before they add the food item that is to be fried. By then, the vitamins and minerals that the oil might contain would have being destroyed. Now, consider the benefits of using and re-using that same amount of oil, whose composition has changed and would have lost its flavour?
“In a case where such used oil is left for a long period of time and it has gone rancid or bad, the oil would have solidified. The colour would have being affected as well. Now, if an individual goes on to cook with such oil, unknown substances that could be cancerous could have being formed.
“The best option is to know the quantity of oil that one needs for frying to prevent the need for its reuse.”
A 2001 parallel review of 20-year dietary fat studies in the United Kingdom, the United States of America and Spain, found that polyunsaturated oils like soya, canola, sunflower, and corn oil degrade easily to toxic compounds when heated. Prolonged consumption of burnt oils led to atherosclerosis, inflammatory joint disease and development of birth defects.
Source:tribune
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