Not nitrogen, plants turn that gas into proteins, and nitrogen is hard to get in an absorbable form for plants. A lot of fertilisers boost nitrogen. The gas involved in ripening fruit is ethylene. A main part of natural gas, burnt in BBQs and gas stoves and ovens. It is also (really) a ripening hormone for fruit and vegetables.
At least here is Australia, it used to be common to “gas” green oranges using piped town gas to turn them orange coloured for sale. Storing an unripe fruit with one producing ethylene will result in speeded-up ripening. A hard avocado, for example, will ripen quickly in a bag of bananas. Conversely, because the ethylene is being used up, the bananas will not over-ripen.
On sale here, and presumably many countries, are green coloured plastic bags, which absorb ethylene, thus preserving fruit and vegetables longer in a fridge.
Ethylene is also used to make poly-ethylene, the plastic.
When first proposed as a plant hormone, many scoffed that such a simple gas (two carbon atoms joined to four hydrogen atoms - nothing like the complexity of other hormones) could be a hormone, but this now fully verified.
You can stop the ripening process by refrigerating bananas. So instead of throwing away half the bunch because they all ripen on the same day you can put them in the fridge when they are just right, a little soft with brown spots, and they’ll stay that way. They will continue to darken in the fridge though. That will help anyone eating a lot of bananas, but I just use the simpler solution of only buying as many as we’ll consume here in a week which is just 2 or 3. And it works out well because my wife for reasons unknown to rational humans prefers unripe hard and still slightly green bananas leaving any that reach the stage of banana nirvana for me.
I remember hearing on NPR (Planet Money, I think) about how bananas became so popular in the US, that there was a massive advertising campaign when bananas were first introduced to US grocery stores, including a jingle with the Chiquita banana girl sternly warning that “You must never, ever, ever put your bananas/ in the refrigerator.”
It was explained in the story that refrigerated bananas stay fresh longer, but they look less appealing, and the banana companies preferred that your bananas go bad and you buy more than that they look unaesthetically black on the outside.
I’m a Chiquita banana, and I’m here to say:
Bananas have to ripen in a certain way.
When they are flecked with brown, and have a golden hue
Bananas taste the best and are the best for you.
You can put them in a salad
You can put them in a pie-ay!
Any way you want to eat them
It’s impossible to beat them!
But bananas like the climate of the tropical equator
So you should never put them in your refrigerator!
No, no, no, no. No no no!
That’s pretty close, I’m certain, to the jingle. Been singing that for 50+ years now.