Compound Accelerates Fruit Ripening, Slows Softening After Harvest

Nutritional experts are urging Americans to eat more fruits and vegetables. Some of us actually are following the advice. So wouldn’t it be great if there was a natural compound that caused fruit to ripen more quickly and last longer on grocers’ shelves and in our refrigerators?

UW–Madison horticulturists have identified just such a compound. The researchers found that it can be used on a wide variety of fruits and vegetables before or after harvest. They are now testing it on cranberries, peaches, tomatoes, grapes and even cut flowers.

“When applied before harvest this compound accelerates the development of fruit flavor and color,” says Jiwan Palta, a plant physiologist in the College of Agricultural and Life Sciences. This month, Palta and his colleagues published a paper in the Proceedings of the National Academy of Sciences describing how the compound extends shelf life by slowing the breakdown of plant membranes after harvest.

Known technically as lysophosphatidylethanolamine, or LPE, the compound can be found in many plant and animal tissues. The Wisconsin scientists are experimenting with LPE purified from egg yolks and soybeans.

When the scientists sprayed LPE on apple trees and cranberry vines two weeks before harvest, the apples and cranberries ripened more quickly and developed a redder color than fruit not sprayed with LPE. The fruit sprayed with LPE before harvest also remained crisp longer in storage.

Palta believes the compound may be especially important to Wisconsin cranberry growers. Cranberries that ripen sooner could translate into increased profits in Wisconsin, where early frosts often force growers to harvest the crop before the berries are completely ripe. Growers typically receive more money for berries that are fully ripened, Palta says.

Currently there is a compound called Ethrel that also speeds the ripening of many kinds of fruit, says Palta. He notes, however, that it is not cleared for use by cranberry growers and cannot be used by organic growers.

Ethrel also can burn plant leaves and cause overripening and softening of fruit, according to Palta. “LPE differs from Ethrel in this regard. Plant foliage remains healthy while LPE accelerates ripening,” he says. “In field tests with tomatoes, the leaf burn that occurs with Ethrel alone was reduced when LPE was added to the spray solution.” Therefore, Palta believes that growers may want to use a combination of the compounds in the future.

Palta and his colleagues have found that LPE not only accelerates ripening but also retards aging of plant tissue. In a recent article in the journal HortScience, Palta and research associate Navjot Kaur showed that immersing snapdragon flowers in an LPE solution overnight extends their life as cut flowers from about four days to about eight days.

“LPE is a common lipid found in plant and animal cell membranes,” Palta says. “We once thought that lipids only played an important role in plants as part of the structure of cell membranes and as an energy source. It’s now clear that they play an important role in regulating cell metabolism.”

In the Proceedings of the National Academy of Sciences, Palta and coworkers Stephen Ryu, Bjorn Karlsson, and Mustafa Ozgen showed that LPE can inhibit the action of phospholipase D by up to 91 percent depending on the concentration of LPE. Phospholipase D, which occurs in both plants and animals, appears to be a key enzyme that controls the breakdown of phospholipids in plant membranes during the early stages of plant aging.

“We know more about how phospholipase D works in animals than in plants,” says Palta. “Scientists have found several factors that speed up the action of phospholipase D. LPE is the first compound we know of from animals or plants that strongly inhibits this enzyme in a specific manner.”

The UW–Madison scientists tested individual parts of the LPE molecule and several forms of LPE before identifying the form of LPE that is the most potent inhibitor of phospholipase D. They also showed that that particular form was the most beneficial one in keeping cranberries from breaking down.

Palta has received patents on both the preharvest and postharvest use of LPE on crops through the Wisconsin Alumni Research Foundation. He has applied for an experimental-use permit from the Environmental Protection Agency.

“We hope to work with cooperators in several major agricultural states. These would be large-scale field trials that test LPE’s effectiveness on cranberries, apples, peaches, grapes, tomatoes and citrus,” he says.