Ethylene gas, a naturally occurring plant hormone, acts as a crucial signal in the maturation process of various fruits. Understanding how ethylene functions helps explain why some fruits continue to ripen after being harvested, while others do not.
Ethylene’s Role in Fruit Ripening
Ethylene gas regulates fruit ripening. It triggers the breakdown of cell walls, leading to fruit softening. Simultaneously, ethylene promotes the conversion of starches into sugars, enhancing sweetness and flavor. The gas also influences the development of characteristic aromas and changes fruit color.
Fruits are categorized based on their ripening behavior in response to ethylene. Climacteric fruits are those that produce a burst of ethylene and experience a significant increase in their respiration rate as they ripen. This means they can continue to ripen even after being picked from the plant. Non-climacteric fruits, conversely, do not exhibit this surge in ethylene production or respiration and therefore will not ripen further once harvested.
Fruits That Produce Ethylene
Many common fruits are known to produce ethylene gas as they ripen, making them capable of continuing their maturation journey after harvest. These climacteric fruits include apples, bananas, avocados, and tomatoes. Other examples are peaches, pears, plums, mangoes, kiwis, and certain melons like cantaloupe and honeydew.
For these fruits, the ethylene they produce acts as an autocatalytic signal, meaning a small initial amount of the gas encourages the fruit to produce even more, accelerating the ripening process. This allows them to be picked when mature but still firm, facilitating transport, and then ripened later. In contrast, non-climacteric fruits, such as cherries, grapes, strawberries, blueberries, and citrus fruits like oranges and lemons, produce very little ethylene. These fruits must be harvested only when fully ripe, as their quality will not improve off the plant.
Managing Fruit Ripening with Ethylene
Knowing which fruits produce ethylene and which are sensitive to it offers practical advantages for storage and ripening. Ethylene-producing fruits, particularly those that are ripe, can accelerate the spoilage of ethylene-sensitive produce if stored together. For instance, keeping apples or ripe bananas next to leafy greens or broccoli can cause the latter to yellow and deteriorate more quickly.
To slow down ripening and extend shelf life, it is advisable to store ethylene-producing fruits separately from ethylene-sensitive vegetables and fruits. Conversely, if you wish to hasten the ripening of an unripe fruit, placing it in a paper bag with an ethylene-producing fruit like an apple or banana can be effective. The paper bag traps the ethylene gas, concentrating it around the unripe fruit and stimulating its maturation. Refrigeration can also slow down the production and effects of ethylene, helping to preserve ripe fruits longer.