Ethylene is a natural hormone, produced by plants, that triggers ripening in fruits. It makes them softer through the decomposition of the major components of the cell wall, such as pectins. It also makes fruits sweeter by converting starch to sugars. Then, flavors and aroma are developed by production of volatile organic compounds.
The technique of controlled ripening of fruits (such as banana, tomato, kiwi and mango) by using ethylene has been carried out commercially for years. You can also use ethylene in your kitchen when you want to accelerate ripening of fruits. To achieve it, place the unripe fruit in a paper bag and add a high ethylene fruit, such as ripe banana or apple, to it.