Wednesday, 19 April 2017

What is the gas inside a capsicum comprised of

Have you ever wondered what the gas inside a capsicum is comprised of?  Or the composition of the gas inside a pumpkin?  Or the composition of the gas inside any hollow fruits?  I have.  

When I was a child every time we would cut open a capsicum or pumpkin I would try to breathe in the gas.  I thought (because school teachers with a limited understanding of biology told me that "plants breathe out oxygen") that it would be almost pure oxygen.  I always wished I had some way to work out the composition of the gas inside a capsicum or pumpkin and be able to know for sure.

When I was in high school I thought if the gas was largely oxygen then I should be able to use the glowing splint test to prove it.  I tried several times, but never had any luck.  I was not sure if this was because the gas was not largely oxygen, or if the gasses mixed with the atmospheric air too much after cutting the fruit open rendering the test useless.  I always wanted to cut open a capsicum under water and capture the gas in an upturned test tube to try the glowing splint test, but I never did.

Now that I am older I still have no way of accurately measuring the components of the gas inside hollow fruits.  I could try to the glowing splint test, but the internet now exists which means that I have access to all kinds of information.  It is like having the world's greatest library.

So I did some research and found the answer.  There were a few forums and things where people made up the answer but mostly got it wrong, I even found a few books of 'facts' where they made up the answer and got it wrong.  None of this impressed me because I wanted to find someone who had measured the composition of the gas inside hollow fruit, not just guess the answer.

I eventually found a few places that actually measured the composition of the gasses inside hollow fruits.  It was strangely difficult to find the answer, so I thought I would share it here.
Hollow tomato fruit
Hollow pumpkin fruit

The gas inside a capsicum and pumpkin
The average concentration of oxygen and carbon dioxide in the atmosphere
20.95% O2    0.4% CO2

The average concentration of oxygen and carbon dioxide inside a capsicum
19% O2    3% CO2 
Oxygen ranged from 18% to 20% and Carbon Dioxide ranged from 0.5% to 3% depending on the stage of growth that the gas was measured.

The average concentration of oxygen and carbon dioxide inside pumpkins
Oxygen ranged from 4% to 16%   Carbon Dioxide ranged from 6% to 8%depending on the stage of growth that the gas was measured.


The results
The gas inside a capsicum or a pumpkin is not high in oxygen or low in carbon dioxide.   Who would have thought!

The oxygen content of the gas inside hollow fruits varies a bit but is always lower than in the surrounding air.  There are some theories that this is due to the seeds requiring oxygen for growth or to reduce the amount of internal fruit spoilage due to oxidation.  It appears that we don't know why it happens at this stage.

The carbon dioxide content of the gas inside hollow fruits varies, but it is significantly higher than in the surrounding air.  There appear to be a few theories about this, again it appears that we do not know for certain.


Further reading

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