Only monosaturated fatty acids (such as butter) are stable compounds and therefore only suitable for heating. Olive oil would still be fairly stable (monosaturated fatty acid) and only suitable for stewing something a little (not too high temperatures), but the polysaturated fatty acids (corn oil, soybean oil, sunflower oil,…) would only be suitable for cold preparations. . They are labile chemical compounds. You should therefore not bake with olive oil at high temperatures because other compounds are then formed. What about all the oils they sell (even those from Becel Bakken and Braden)?
Answer
Dear Ms,
You’re right, but I’d narrow it down a bit.
The core idea is correct: the more unsaturated a fat/oil is, the more sensitive it is to oxidation and since oxidation is accelerated at high temperature, you can also say that the more unsaturated an oil is, the less suitable it is for heating.
However, we have to nuance something. Olive oil is especially rich in oleic acid which has one unsaturation (we call this a double bond, indicating the presence of a double bond between 2 carbon atoms; in a saturated fat, this is only a single bond). Oleic acid is actually quite stable. It is only when 2 and actually especially from 3 or more double bonds in the same fatty acid that an oil will become very sensitive to oxidation. That is why oils such as corn, sunflower, groundnut that mainly contain linoleic acid (2 double bonds) (50-60%) can still be used for heating applications. However, soy oil, which contains linolenic acid (8-10%, 3 double bonds) in addition to linoleic acid (55%) is not suitable for heating applications due to the greater presence of linolenic acid.
You can therefore perfectly heat in olive oil and corn oil, even in frying applications. Please note: unlike a deep-frying oil, you need to change a deep-frying oil fairly regularly. As a rule of thumb you can say that you can use a frying oil 6-8 times, depending on what you are frying: fries 8 times, brochettes, croquettes, fish sticks, etc., 6 times. This is because the latter matrices release more substances than French fries that accelerate the oxidation process. You can also see this: the oil gets thicker (at room temperature) and dark – the thickening is actually a polymerization of the oil (think of the old varnish that is based on linseed oil; linseed oil contains 50% linolenic acid and thus actually oxidizes spontaneously at room temperature causing it to form a film).
Butter in itself is sensitive to burning, because there is still a bit more in butter than fat: it also contains proteins and some lactose; ideally you should melt the oil and only work with the so-called butter oil (the fat above, without white watery mass at the bottom).
The fat or oil blends marketed specifically for heating will be suitable for heating. I don’t rule out the possibility that some contain limited amounts of linolenic acid (typical cooking oils that may not be heated repeatedly). This is not necessarily a problem, but I would strongly advise against repeatedly heating an oil with more than 5% linolenic acid. Rapeseed and soybean oil are the most common oils with linolenic acid in them, both about 10%. Walnut oil also contains the same amount, but this is more of a special oil that it would be a shame to heat because of the typical taste. Mixtures may contain typical rapeseed; especially eg salad oil.
Hoping this has given you some clarification.
Regards
Bruno De Meulenaer
Answered by
Prof. Dr. ir. Bruno De Meulenaer
Food Science Food Chemistry
http://www.ugent.be
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