A recent study of heat stability of common cooking oils has shown that olive oil is more stable at high heat than other common cooking oils.
In the study, a range of common cooking oils was heated to high temperatures and the number of dangerous oxidative by-products produced by each oil was measured. It was shown that extra virgin olive oil produces fewer dangerous oxidative by-products on heating than other common cooking oils. The results contradict many previous studies that correlate the smoke point of an oil with its heat stability; in fact, smoke point is not a good indication of oil degradation.
Compared to cooking oils with high levels of polyunsaturated fats, such as canola oil, extra virgin olive oil was shown to produce low levels of polar compounds and oxidative by-products. The researchers found that when heated, oils with high fatty acid profiles and natural antioxidant content (such as extra virgin olive oil) were more stable than oils with high levels of polyunsaturated fats (PUFAs).
Ten of the most commonly used cooking oils in Australia were tested:
- extra virgin olive oil
- virgin olive oil
- olive oil
- canola oil
- rice bran oil
- grapeseed oil
- coconut oil
- high oleic peanut oil
- sunflower oil
- avocado oil
What happens when you fry food in oil?
When heated to high temperatures for frying, oil decomposes into a variety of volatile compounds and monomeric and polymeric products. These can affect the way the fried product tastes, and how healthy it is. Some of these compounds are responsible for the pleasant flavor, taste and the typical crispness and golden colour of fried food. After a while, the oil may become more viscous, it may darken in colour, and it may foam more.
How was heat stability tested?
The researchers ran two trials:
- In the first trial, 250mL of each oil was heated to 240C, and samples were taken at regular intervals
- In the second trial, 3 litres of each of the oils was heated to 180C in a deep fryer, and held at that temperature for six hours. Samples were taken at regular intervals.
Each sample was tested for characteristics of degradation: smoke point, oxidative stability, free fatty acids, polar compounds, fatty acid profiles and UV coefficients.
Based on the average level of final polar compounds at the end of both trials, extra virgin olive oil ranked first, followed by coconut oil. The table below also shows that smoke point is not a good indicator of oil stability when heated.
|Oil type||Final polar compounds (%)||Smoke point (oC)|
|Extra virgin olive oil||8.47 ± 1.841||206.67 ± 2.520|
|Coconut||9.30 ± 0.415||191.00 ± 3.610 50.|
|Virgin olive oil||10.71 ± 2.337||175.33 ± 0.577|
|Peanut||10.71 ± 4.159||226.33 ± 2.080|
|Avocado||11.60 ± 1.401||196.67 ± 0.577|
|Rice Bran||14.35 ± 1.433||237.00 ± 1.730|
|Sunflower||15.57 ± 6.770||254.67 ± 1.530 6.|
|Olive oil||11.65 ± 0.836||208.00 ± 1.530|
|Grapeseed||19.79 ± 0.502||268.00 ± 1.000|
|Canola||22.43 ± 5.609||255.67 ± 0.577|
Extra virgin olive oil was shown to be the most stable oil when heated, followed closely by coconut oil and other virgin oils such as avocado and high oleic acid seed oils.
Key findings are:
- smoke point does not predict an oil’s performance when heated
- oxidative stability and UV coefficients are better predictors when combined with total level of polyunsaturated fats
- of all the oils tested, EVOO produced the lowest level of polar compounds
- production of polar compounds was more pronounced for refined oils
- EVOO was the most stable oil when heated, followed closely by other virgin oils
What’s wrong with oxidation of oil?
A number of experiments have shown that oxidized vegetable oils can cause damage to brain cells, lead to inflammation, and increase the risk of diabetes and cardiovascular disease.
de Alzaa F, Guillaume C, Ravetti L. Evaluation of Chemical and Physical Changes in Different Commercial Oils during Heating. Acta Scientific. 2018;2(6):2-11.