Which Oils are best for frying?

There are many questions I am asked as a food scientist and among the many, ‘Can I use olive oil for frying? Is the most popular.

I used to start lecturing on saturated fats, smoke points, mono-unsaturation, and poly-unsaturation. Then, I used to dive into the world of minor components, bioactive compounds, antioxidants, and so forth.

There isn’t an answer that I can give that does not start with a description of the different sources of fats that we use for cooking so, have a seat, adjust your glasses to your noses, I will answer this question by taking my time.

Fats and oils are divided into solids and liquids. Solid fats are made mostly of saturated fatty acids and if you want examples they are butter and lard among the many. The presence of saturated fats makes them great plastic fats to work with, especially for bakery products. On the other hand, they are also associated with increasing low-density lipoprotein (LDL) cholesterol, which is a major risk factor for cardiovascular diseases (CVD).

Liquid oils are characterised by high percentages of unsaturated fatty acids (with one C=C or more) that notably make the liquid oils healthier sources of fats.

Frying with oils has been at the centre of a debate for a while. Indeed we need to use liquid oils as their smoking point is higher, thus making them more stable (liquid oils are also healthier). Each oil will then have its patter in terms of fatty acids that will more or less likely be susceptible to oxidation. Oxidation is one of the things that is boosted when oxygen, light and a source of heat are present alongside unsaturated fatty acids. We want to avoid this as much as we can.

One of the best characteristics an oil can have to be used especially for deep frying is to:

  • have high unsaturated fatty acids vs polyunsaturated fatty acids ratio
  • presence of bioactive compounds such as antioxidants to protect the oil from oxidation
  • having a high smoking point that will ensure oils’ stability during frying

Smoking Point

But let’s go back a little and let me explain what an oil smoking point is. Imagine heating some oil in a pan, what will happen if you leave it there for too long or if you forget about it (extremely dangerous) is that the triglycerides will eventually break down into glycerol and free fatty acids (glycerol will keep breaking down) and will produce a cloud of very thick smoke. Your oil might also catch fire so watch out.

The smoke point changes from oil to oil and depends mostly on the amount of free fatty acids present. The more FFA we have, the lower is the smoking point.

If you are looking into an oil for deep frying, you should choose one with a high smoke point!

Oxidation

Oxidation is also one enemy of oils (and foods in general). It is a chain reaction that is boosted by the presence of radicals, oxygen, light and heat, which is why oil bottles are in amber glass and should be kept away from heating sources, especially when you are cooking.

Oxidation is also dependant on the number of unsaturations (C=C) we have in our oils which means that monounsaturated oils will be more stable than other polyunsaturated ones. This is why we have commercially available high oleic sunflower oil vs the regular sunflower oil.

High oleic sunflower oil (HOSO) is characterised by having a high percentage of monounsaturated fatty acids (80% of oleic acid). Sunflower oil in general is also a natural source of Vit E which is a renowned antioxidant as well, something we can find in HOSO.

The presence of higher mono-unsaturation and the Vit E will make the high oleic sunflower oil a good and relatively cheap oil to use especially for deep frying.

High Oleic Sunflower Oil vs Olive Oil

Olive oil, on the other hand, is a highly monounsaturated oil and perhaps one of the best sources of fat we could find in nature. As I said, its high level of monounsaturated fatty acids and the presence of a powerhouse of antioxidant bioactive compounds will make this very stable and protect the matrix from oxidation phenomena or at least slow it down.

Of course, we have different types of olive oil: extra virgin olive oil, virgin olive oil and olive oil and they are classified based on the amount of free fatty acids present (read more in the specific EU regulation: EC 1234/2007).

Extra virgin olive oil is one of the best oils to be used crude to dress salads for example and is just too precious to be wasted for deep frying but this of course is my own opinion and nobody will stop you from frying with EVOO if you want to – it is still a great high-quality fat.

Olive oil contains 55 to 85% of monounsaturated oleic acid which is more resistant to oxidation than any other polyunsaturated fatty acids. Olive oil is also stable during frying if you look at its smoking point which is set around 210°C. High oleic sunflower is between 200 – 225°C very similar to olive oil.

In general, frying with olive oil might bring some benefits thanks to the composition of the oil itself, however, considering the amount of oil normally used for deep-frying, perhaps the use of olive oil might not be necessarily cost-effective and as an alternative, high oleic sunflower oil would work too.

References

De Souza, R., Mente, A., Maroleanu, A., Cozma, A., Ha, V., Kishibe, T., Uleryk, E., Budylowski, P., Schunemann, H., Beyene, J. and Anad, S. (2015) ‘Intake of saturated and trans unsaturated fatty acids and risk of all-cause mortality, cardiovascular disease, and type 2 diabetes: Systematic review and meta-analysis of observational studies’, BMJ (Online), 351, pp. 1–16.

Mensink, R. (2016) Effects of saturated fatty acids on serum lipids and lipoproteins: a systematic review and regression analysis. Geneva: World Health Organization.

World Health Organization (WHO) (2019) ‘REPLACE Trans Fat’, World Health Organization, pp. 1–8.

Fauziah, A & Razali, I & Aini, Nor. (2000). Frying Performance of Palm Olein and High Oleic Sunflower Oil During Batch Frying of Potato Crisps. Palm Oil Dev. 33.

Matthäus, Bertrand. (2006). Utilization of high-oleic rapeseed oil for deep-frying of French fries compared to other commonly used edible oils. European Journal of Lipid Science and Technology. 108. 200 – 211.

Council Regulation (EC) No 1234/2007.

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