Speaking of bananas.

The combination of green stalks and brown spots in a bunch of bananas is indicative of
chemical ripening; black stalks indicate a naturally ripened banana.

Can You Tell If a Banana Is “Chemically Ripened” by Looking at It?
If the banana you are looking at came from a supermarket, it’s almost certain to have
been ethylene treated anyway.
When calcium carbide is dissolved in water it produces acetylene which acts as the
artificial ripening agent but taints the fruit with arsenic . Many bananas and other
fruits are chemically ripened using ethylene gas. Bananas naturally produce ethylene
gas, which causes the fruit to ripen on its own.