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Are PAHs produced at the same rate when microwaving olive oil?

Answered on August 19, 2014
Created December 21, 2010 at 8:46 PM

I'm aware that olive oil makes a poor cooking oil due to the creation of toxic PAHs when it is heated. I was wondering if reheating foods in the microwave that had raw olive oil added after cooking will result in the production of PAHs.

If I take two samples of extra virgin olive oil, heat one on the stove and one in the microwave to the same temperature, will more PAHs exist in one of the samples?

35a9207254408c6907f7082640c7bfaa

(822)

on December 22, 2010
at 06:23 PM

In the study they heated oil to over 200 C in the microwave which is 392F. I'm sure you could get it hotter if you tried.

47a42b6be94caf700fce9509e38bb6a4

(9647)

on December 22, 2010
at 04:04 AM

How about stopping the microwave frequently to mix the food.

D30ff86ad2c1f3b43b99aed213bcf461

on December 21, 2010
at 08:55 PM

I like this question.

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2 Answers

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35a9207254408c6907f7082640c7bfaa

(822)

on December 22, 2010
at 02:32 AM

This paper seems to argue that it's mostly direct contact with flame that causes PAH contamination during cooking. It says that vegetable oils' primary source of contamination is the processing/deodorizing procedure, so cold-pressed olive oil might be safer.

For normal low-fat foods microwave is a low-temp cooking method since water absorbs most of the energy and it will evaporate at 212F. It's hard to heat the water beyond that point and a lot of it will just leak out of the microwave. Unfortunately fats and oils seem to be heated preferentially by microwaves (see http://www.cazv.cz/attachments/CJFS_23_230_239.pdf). That's bad because it means the oil will be getting hotter than the rest of the food and the oil will not evaporate at 212F like water does.

Microwaves don't heat evenly and so some of the oil might be in the oxidation danger zone while the rest of your food is still pretty cold. That paper actually observed more oxidation of olive oil in the microwave compared to a conventional oven under similar conditions. I think oxidation is a bigger concern than PAH formation in the microwave.

One way to microwave fats more safely might be to use a lower power setting, since it would give the oil more time to cool down by transferring heat to surrounding food mass that cannot be directly heated by the microwave radiation in between magnetron cycles. The maximum temperature of any oils in the food should be lower during the entire cook cycle that way, even if you cook for a somewhat longer period of time. Just a theory, though.

Another approach: only cook/heat low-fat foods in the microwave. Add fat after cooking or heating.

47a42b6be94caf700fce9509e38bb6a4

(9647)

on December 22, 2010
at 04:04 AM

How about stopping the microwave frequently to mix the food.

1
22937fffe2210014f24939becf23b1b3

on December 22, 2010
at 02:06 AM

I am only speculating... but, I think you're safe, the oil will not be hot enough for long enough for oxidization an to occur. Generally you want to stay away from the smoke point. The smoke point for olive oil varies depending on the source, but less 220F-350F is generally considered safe. The temp of your food would not likely be that hot. If you are that concerned, use alternative fat like coconut oil, lard, ghee, etc.

35a9207254408c6907f7082640c7bfaa

(822)

on December 22, 2010
at 06:23 PM

In the study they heated oil to over 200 C in the microwave which is 392F. I'm sure you could get it hotter if you tried.

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