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This is a question about the biology of microorganisms, not about food safety.

While most of our foods spoil quite quickly (it is recommended to throw food away after 2h in the danger zone), for some oils this is not the case: for example, opened olive oil may be kept for 18 or more months at room temperature.

This seems to indicate that while there are plenty of microorganisms around, pathogenic or otherwise, which readily feast on carbohydrates or proteins, there do not seem to be that many (or at least not in practically relevant amounts) that can metabolize our food oils, while our stomachs have no problem with that.

Why is this? Is it hard for microorganisms to break down the fatty acids (if so, for what reason), or do these oils usually have secondary constituents which are poisonous to microorganisms, but not to us?

Note that some bacteria can use fatty acids as energy source; that makes it even more interesting why it doesn't occur in our kitchens...

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  • $\begingroup$ Oil Rancidification is a good read: en.wikipedia.org/wiki/Rancidification $\endgroup$
    – Science123
    Jul 7, 2021 at 12:46
  • $\begingroup$ There are plenty of foods that conserve long time after being open - sugar, flour, cereals, water, etc. This is to say that one needs to narrow the class of foods in question - which may already contain the answer. $\endgroup$
    – Roger V.
    Jul 7, 2021 at 12:52
  • $\begingroup$ That was a very interesting read, thanks @Science123, though it looks at it more from the point of view of the oils themselves (ie., also processes like autoxidation which do not involve microorganisms). Like the link I have in the question it also mentions E.Coli, and that there are natural anti-oxidants like Vitamin E... now the question remains - are these oils so chok full of anti-oxidants/microorganism killers that those have no chance; or are there little no no microorganisms that can survive on oils in the first place (and if so - why)... $\endgroup$
    – AnoE
    Jul 7, 2021 at 14:08
  • $\begingroup$ True, @RogerVadim, but I fear if I open up the question for all kinds of stuff ("why do some kinds of foods not spoil") it may be a little too generic... $\endgroup$
    – AnoE
    Jul 7, 2021 at 14:09

1 Answer 1

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Bacteria and other Microorganisms are mostly water, and to replicate they will need more water. The water they need is not present in olive oil. Salts and other required elements are also not present in olive oil, at least not in sufficient quantities to support proliferation of microorganisms.

Our stomachs indeed have no problem metabolizing oil, but if you had nothing else to eat or drink, you would die in short order.

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  • $\begingroup$ Oh man, in hindsight the water aspect really seems quite trivial, and incidentally also answers why stuff doesn't grow on very dry stuff in general (pure sugar etc.). Thanks for opening my eyes! $\endgroup$
    – AnoE
    Jul 8, 2021 at 7:06

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