Frying Oil - Safety

SAFETY OF FRYING OILS AND OIL FRIED PRODUCTS

What can happen to frying oils?

Vegetable oils or frying oils are reactive substances that can undergo chemical changes during storage, heating or exposure to light. These chemical changes can create "breakdown products" in the oil, which are potentially harmful substances.

The common obvious changes are a darkening of colour, a thickening, a rancid odour, and sometimes a rancid taste. However, some breakdown products can only be detected by chemical laboratory analysis.

Oxidation is a major reason for the chemical breakdown of oil, but there are several other causes of degradation with potentially toxic effects. When oil contains more than specific levels of breakdown products, it is classified as "abused oil" or "over-used oil".

It is important to note that not all oil breakdown products are potentially harmful. Some products are harmless and are normal products of digestion.

The speed of breakdown and level of breakdown products formed depends on the type of oil; as the higher the amount of unsaturated fatty acids (monounsaturates and polyunsaturates) the higher the rate of breakdown. Also, polyunsaturated oils, including soy, sunflower and canola, may have lower stability than monounsaturated oils like olive and palm oils.

While the type of oil used makes some difference to the formation of breakdown products, it is proper oil management that is the key to preventing this degradation. Effective oil management means the rigid control of frying temperature and frying time, and minimising the presence of compounds that can trigger breakdown (such as food particles and minerals like copper, iron and zinc).

Oil management is important in restaurants, fast food outlets, and in other industrial processes, as well as in the home, where the proper handling of used oil for repeated use will make a significant difference to the useful lifespan of the oil.

For the person cooking at home, effective oil management practices mean:

• Maintaining a frying temperature of 180°C or below.
• Using stainless steel frying vessels, and not iron, copper or galvanized.
• Cooling oil after frying, and not leaving it oil hot and idle.
• Storing used oil in glass or stainless steel, in the dark.
• Straining out as much foreign matter as possible at the end of each frying session.
• As far as possible, removing all traces of old oil (which forms a brown sticky varnish substance) from the cooking vessel surfaces that come in contact with hot oil. "Varnish" is an oxidation product, and this varnish catalyses degradation.

There is concern about the formation of harmful oil breakdown compounds and their effect on human health.

Although studies have shown a negative impact of these breakdown products on animal health, including growth retardation, enzyme imbalances and increased liver and kidney weights, no conclusive results on the effect on human health have been published in scientific literature. It is not clear at what level of intake the breakdown compounds may become a health hazard.

Another concern is that abused oil is more readily absorbed by foods than fresh oil during food preparation. This increases the level of potentially unhealthy breakdown compounds in the food, and also increases the energy (kilojoules) consumed.

A third concern is that there have been reported instances of unscrupulous food processors selling abused oil to low-income consumers for household use. This is an irresponsible and unacceptable practice; used frying oil should be taken out of the food chain.

After a national survey by the Department of Health on oil abuse by frying establishments across South Africa in 1995, the South African Government published Regulation No. 17365 - in the Government Gazetteof 16 August 1996 under the Foodstuffs Cosmetis and Disinfectants Act 54 of 1972. About six countries, mostly European, have passed national legislation to prohibit the sale and distribution of oil that exceeds the allowed level of "toxic indicators".

Codex Alimentarius, an international body that sets international standards and guidelines for food products, has not introduced standards. The World Health Organisation reviewed current scientific literature and reported that: "Many studies show that certain extracts fed at high dietary levels can trigger adverse effects in animals, but these studies are of limited use in providing a basis for assessing the safety of these compounds at levels normally present in used oil."

So does the consumption of abused oil at normal intake levels pose a risk? There is enough evidence to show that, in excess, most compounds are toxic, but that the level of intake in normal diets does not necessarily mean that consumption must be restricted. The benefits of fats and oils in the diet, especially in lower income groups, must also be weighed up against the potential risk of poisoning by "indicators of toxicity". Risk assessment is thus an important consideration in this debate.

There is, though, a nutritional concern: The polyunsaturated (essential) fatty acid levels in abused oils will be low. Similarly, the tocopherol (vitamin E) content of over-used oil will be practically zero.

How can you reduce the risk of potentially harmful breakdown products?

• Oil users must follow a code of practice in terms of oil management, both in industrial processes and at home. Although one company issues a certificate of compliance with an approval logo to certify that its oil complies with certain standards, this logo can create a false sense of security if standard oil management practices are not followed. A certified or approved oil can still be abused by the user, whether industrial, catering or household.
• Consumers should only buy oil from reputable suppliers and practice good oil management in the home.
• Consumers must be well informed on the recommended or preferred applications of different oil types.
A national Code of Practice should be introduced to promote and ensure the safety and quality of edible oils.

More information can be found at: http://www.fehd.gov.hk/publications/text/oil.html