Postharvest Ethylene Applications for Color Change

A citrus fruit’s color can provide the appearance that it is not ready to be harvested. But internally, it could be ready to eat.

To help convince consumers of the citrus crop’s readiness, Angelos Deltsidis, University of Georgia assistant professor and postharvest Extension specialist, is researching the use of ethylene to artificially degreen citrus after harvest.

“Naturally, citrus changes color when the temperatures drop below 55 degrees Fahrenheit. This can happen in the environment when we have such low temperatures in the fall. If we don’t have them, however, the fruit will not change to its characteristic external color, even if it is ready to be eaten inside,” said Deltsidis.

The color change can be achieved by using ethylene, a natural plant hormone that has the form of a colorless gas. When supplied at the appropriate temperature and concentration, it stresses the fruit and cause it to change color after harvest.

“When the conditions are such that the fruit doesn’t change color naturally, we can do that after harvest by putting the fruit in a room and supplying ethylene,” Deltsidis explained.

He emphasized that nothing changes with the internal quality of the citrus when this management tactic is implemented. The fruit still exhibits the same sweetness it is known for. Externally, it changes from a green to orange or yellow, depending on the fruit.

“You can have a great looking orange, but it’ll be green, and people will be like, ‘It’s not good.’ By doing the artificial degreening, you give them what they want,” Deltsidis said. “Unless it is lime, nobody would buy a green citrus. In our mind, citrus fruits have to be either orange or yellow. For grapefruit, we don’t have this problem as much, but for satsumas we have it. Different cultivars have different sensitivities and different requirements.”

The degreening process requires two to three days. Growers need a temperature-regulated room to gas their fruit with a tank of ethylene or ethylene generator. Be certain to pay attention to ethylene levels, as buildup of ethylene can be explosive in very high concentrations.