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This is inspired by a recent popular question on Cooking.

Let's assume that I take some apples, cut them up, and place them in a hermetically sealed container. Then the container goes into the fridge. The apple pieces will start to get brown, because some of the apple molecules are reacting with oxygen (enzymatic browning). Obviously, since the container is now sealed, this reduces the total amount of oxygen in the container.

Now I had an interesting discussion in comments with another user - their intuition told them that this browning reaction will use up the oxygen so quickly that the apple will brown less than when held in a place with a normal atmosphere. My intuition went to the other direction - that so little oxygen will be used up, that the apple will brown as much as when exposed to unlimited quantities of air. I tried to look up some numbers, but didn't trust my rusty high-schoo-chemistry knowledge enough even for back-of-the-envelope calculations. So here my question: how much of the oxygen will be used up? Especially, will browning stop earlier than with unlimited air?

An interesting side question would be: if the browning does use up significant amounts of oxygen, which will stop the browning first, the system running out of oxygen, or the system running out of the necessary enzymes? But that's an optional question, since getting data on the enzymes may be too complicated.

I am aware that there are too many degrees of freedom for an exact answer. I am perfectly happy with an answer which describes the magnitude of the effect in a way that is easy to grasp, or gives a range for the expected oxygen concentration (even if it's a wide range). To make it more answerable, here are some assumptions:

  • let's define a container with 100 g of apple and 100 ml air
  • since I expect that only molecules on the apple's surface will react, I would be interested in a discussion of the two possible extremes - either an apple cut in half (let's assume that's 40 cm^2) or an apple hacked into many small pieces for maximum surface, but not pureed (I don't know how to calculate the surface, does chemistry offer a formula for the minimum particle size before air stops being able to flow through the particles?)
  • the container is held at 4 Celsius (I hope we can ignore the time in which it cools down from kitchen temperature - but it is filled at kitchen temperature, I don't know if the effect on the total amount of oxygen is significant)
  • we can keep the apple for a maximum of 5 days before we declare it inedible
  • we are not using any methods to slow down browning. Just cut the apple, close the container, let it sit undisturbed.
  • I found a source measuring the amount of phenolic compounds in apples: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4665438/#:~:text=In%20general%2C%20the%20polyphenolic%20contents,per%20apple)%20%5B22%5D. As far as I can tell, the relevant measurement is the 75.7 to 93.0 mg of total phenolic compounds per 100 g of apple flesh, so let's round to 80 (I'm somewhat puzzled by the abbreviation GAE, maybe you know what it is?). I am aware that it lists many different compounds, but I hope that the reactions they do use up a relatively similar number of oxygen atoms, up to a small numeric constant (so maybe compound A reacts with 2 atoms of oxygen and compound B with 3 atoms), so that should be enough for estimating a range.
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  • $\begingroup$ I think your intuition is OK - even so little air wouldn't be much problem. $\endgroup$
    – Mithoron
    Aug 11 '20 at 15:40
  • $\begingroup$ @Mithoron I hope you don't mind that I would like something more than an intuition, even though I admit that a chemist's intuition is much more valuable than mine. My nagging "but what if..." voice will be satisfied much better by somebody doing a quick-and-dirty calculation sketching out the magnitude, and besides, maybe there are effects here which I am overlooking completely. $\endgroup$
    – rumtscho
    Aug 11 '20 at 15:43
  • $\begingroup$ Sure, sure. BTW it's one of things that experiment would tell best and pretty easily ;) $\endgroup$
    – Mithoron
    Aug 11 '20 at 15:51
  • $\begingroup$ Good question that might serve as the basis for some experiments, and could even be done at home in safety by students! They might use the amount of air as a variable, going from ~none (e.g. heat-shrink plastic wrap) to 100 ml. Antioxidants, such as ascorbic acid, could also be a variable. And when they're done, they can even eat the somewhat-browned apples ;-) $\endgroup$ Aug 11 '20 at 18:04

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