UNIVERSITY PARK, Pa. -- Consumers perplexed as to why produce purchased days earlier seems to go bad too quickly may find the culprit is ethylene, an odorless, colorless gas released by fruits and vegetables, say two horticulture specialists in Penn State's College of Agricultural Sciences.

"Ethylene is a gaseous ripening agent released by most fruits and some vegetables," says Peter Ferretti, professor of vegetable crops. "Even in the reduced temperatures within a refrigerator, the gas can cause produce to wilt, spot or go bad."

Ferretti says the solution is fairly simple: separate produce that is sensitive to ethylene from the produce that emits large amounts of the gas.

Kathleen Brown, associate professor of postharvest physiology, says most tree fruits produce large amounts of ethylene, particularly apples and pears. Other high ethylene producers include apricots, avocados, cantaloupes, nectarines, papayas and peaches. Bananas, peppers and tomatoes also produce ethylene, but only when they reach full ripeness.

Produce that is sensitive to ethylene includes:

--Carrots and Parsnips. "Both of these vegetables get very bitter when exposed to ethylene," Ferretti warns.

--Broccoli, Brussels sprouts, cabbage, cauliflower, celery, collards, kale, lettuce and spinach. "These vegetables will turn yellow and go limp from too much ethylene," he says.

--Cucumbers. Ferretti says cucumbers will turn yellow, go soft and develop mushy spots.

--Asparagus. "Asparagus will turn tough or woody," Ferretti says.

--Iceberg Lettuce. "Ethylene causes rust-colored spotting, similar to the injury color you see on lettuce when you cut it with a knife," Ferretti says.

--Squash. All types of squash will develop soft spots and turn yellow from overexposure to ethylene. "Most people don't store winter squash -- like acorn squash -- in the refrigerator, but zucchini and summer squashes can go bad if stored with ethylene producers," Ferretti says.

--Herbs. Parsley, marjoram and mint are the most common herbs that are sensitive to ethylene.

--Apples. Although apples are one of the highest producers of ethylene, the fruit also is sensitive to the gas. Prolonged exposure to ethylene turns apples mealy or less crisp. "Low temperatures reduce sensitivity to ethylene," Brown says. "It's best to store apples in the refrigerator unless they are under-ripe."

"All you need to do is to put the ethylene-sensitive produce in paper bags, roll them shut, and place them in one crisper," Ferretti says. "Those items that produce large amounts of ethylene should be bagged and stored in a separate crisper."

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EDITORS: For more information, contact Peter Ferretti at 814-863-2313.

Contacts: John Wall jtw3@psu.edu 814-863-2719 814-865-1068 fax