What is Ethylene Gas & How is it Used?

What is Ethylene Gas?

Ethylene gas (C₂H₄) is a colorless gas that is naturally occurring as a plant growth regulator in fruits and vegetables. It is naturally occurring, but can also be added to help further along production practices, such as applying ethylene prior to harvest for walnuts to help with harvest, or applying ethlyene gas to unripe bananas that have already been harvested and will react with the ethylene to start their ripening process. 

Why is Ethylene Gas Used in Fruit Ripening?

Ethylene gas is used to jumpstart the fruit ripening process, or to move it farther along. When ethylene gas is used on climacteric fruit (fruit that continues ripening after harvest) that produce large amounts of ethylene gas naturally on their own, exogenous (external) ethylene stimulates the production of ethylene within the fruit itself. Thus, being exposed to ethylene gas results in the fruit producing more ethylene gas internally, and therefore, results in faster ripening of the fruit. 

At home, this relates back to the example of placing a piece of unripe fruit (e.g., a hard pear) in a bag with a banana to ripen it. The banana gives off ethylene gas to the pear and, in turn, the pear is able to ripen itself. But, what they also forget to mention is that the bananas are exposed to additional ethylene in the bag and it also furthers along their ripening process as well!

This same concept is used on a larger scale in fresh fruit handling. The most common example I think we are all familiar with is the banana.

Ethylene Gas Used on Bananas

The bananas consumed in the U.S., Europe, or anywhere outside of the banana growing regions are never harvested ripe. They are transported to the nearest warehouse distribution center, are placed in ethylene chambers for ripening and are sent off to the grocery store. Due to the ethylene exposure, the bananas are able to ripen on their own. Then, while on the display shelf, they continue ripening at an altered speed because they are in the presence of other bananas that are producing and giving off ethylene gas as well.

Some other common examples of fruit that are exposed to ethylene gas for ripening include:

• Avocado
• Mango
• Kiwifruit
• Plum

Other Uses for Ethylene Gas on Fruit

Ethylene De-Greening

Ethylene gas can be used to de-green citrus and other crops (e.g., pineapples). For these particular fruits, ethylene gas only alters their appearance and does not aid in their ripening process. Ethylene gas works to remove the overlying chlorophyll (green color) to unmask the color underneath. In the case of an orange, if it were kept on the tree longer prior to harvest, it would de-green on its own and the skin would be orange when harvested. However, if growers harvest the oranges early to get them to the market, they can apply ethylene gas to the harvested fruit to remove the remaining green from the skin to result in a more saleable product. You have seen this process before on the behind the scenes post on Cuties mandarins.

Ethylene Used Pre-Harvest

Ethylene can also be applied prior to harvest to aid in the harvesting process. One common example is walnuts. Ethephon is applied pre-harvest to aid in the shaking process of removing the nuts from the tree during harvest.

Harmful Effects of Ethylene

Although ethylene gas is strategically used to benefit certain produce items, it can also be harmful for others, especially since ethylene can affect all portions of the plant: the plant, leaves, flowers and fruit. Some examples include:

• Fruits ripen too quickly – If too much ethylene is applied, or it is not applied at the right frequency, then fruits can ripen too quickly. This can result in an unsaleable product.
• Yellowing of vegetables – Some ethylene-sensitive vegetables (e.g., broccoli, cabbage) yellow in the presence of ethylene. You might have seen this before in your local produce department, where the heads of broccoli are yellow, or the cabbage leaves are tinted yellow.
• Flower senescence/abscission – Flowers do not react well in the presence of ethylene. For flower growers, one of their main concerns is that their flowers do not come into contact with any climacteric fruit during shipping so that their flowers do not have any adverse reactions to ethylene. Common examples of ethylene contact with flowers results in leaf abscission on the stems of the flowers (where the leaves fall off) and increased senescence (aging) of the flowers.

If you enjoyed this post, you might also like:

• Stop Ripening Wrong: Climacteric vs. Non-Climacteric Fruit
• Why Don’t My Store-Bought Tomatoes Taste Good?
• Avocado Harvest & Packing