The Role of Ethylene in Fruit Ripening
Most fruits produce a gaseous compound called ethylene that starts the ripening process. Its level in under-ripe fruit is very low, but as fruit develop, they produce larger amounts that speed up the ripening process or the stage of ripening known as the “climacteric.” The level of ethylene and rate of ripening is a variety-dependent process. Some apple varieties such as McIntosh, produce prodigious amounts of ethylene and are difficult to store once this occurs. When harvested after the rapid rise in ethylene, they quickly soften and senesce in storage. Other varieties have a slower rise in ethylene and slower ripening rate. For apples that will be stored longer than two months, it is imperative to harvest them before the level of ethylene begins its rapid increase.
Plums and peaches are also sensitive to ethylene and will continue to ripen after harvest in response to this hormone. Some varieties of plums, such as Shiro, ripen very slowly since ethylene production is suppressed. With these suppressed-climacteric types, fruit may remain under-ripe if harvested too early. Other plum varieties such as Early Golden ripen very rapidly. In this case, harvest should be timed more precisely so that fruit are not over-ripe when they reach the consumer.
To measure ethylene, expensive instruments are needed. This is often done by specialized labs and sometimes by Cooperative Extension to determine if fruit in a general region are still at a stage where they can be stored long-term. Cheaper methods can be used to measure stage of ripeness, but are not as precise as measuring the level of ethylene in fruit.
Methods of controlling ethylene in fruit include preharvest application of aminovinylglycine (ReTain), postharvest application of 1-methylcyclopropene (SmartFresh), cold storage, controlled atmosphere storage, and ethylene scubbing or removal.