Have questions about Ethylene? This is the place for answers!
Ethylene is a natural plant hormone.
It affects the growth, development, ripening, and senescence (aging) of all plants. It is normally produced in small quantities by most fruits and vegetables. Many fruits produce larger quantities of ethylene and respond with uniform ripening when exposed to an external source of ethylene. Ethylene can promote ripening in tomatoes, bananas, citrus, pineapples, dates, persimmons, pears, apples, melons, mangos, avocados, papayas and jujubes – a clear indication that the action of ethylene is general and widespread amongst a number of fruits. It is clear that ethylene is a ripening hormone – a chemical substance produced by fruits with the specific biological phenomenon of accelerating the normal process of fruit maturation and senescence.
Is Ethylene Application an ‘artificial’ process?
Absolutely not. The additional externally applied ethylene merely accelerates the normal ripening process. Numerous studies have shown that there are no important biochemical, chemical, or physiological differences between fruit ripened where the naturally produced ethylene has been the triggering mechanism or where additionally externally applied ethylene has triggered the process in the mature but unripe fruit.
Ethylene is Generally Recognized as Safe (GRAS); Calcium Carbide is NOT.
Given the numerous amounts of food substances, the The United States Food and Drug Administration (FDA) does not categorize every one. Salt, pepper and vinegar are examples. These, along with ethylene, all are within the category of food substances that, when used for the purposes indicated, in accordance with good manufacturing practice, are regarded by the FDA as generally recognized as safe (GRAS) for such uses.
Calcium Carbide is used in some countries as source of acetylene gas, which is an artificial ripening agent. However, acetylene is not nearly as effective as ethylene, and is not a natural plant hormone like ethylene. Also, calcium carbide may contain traces of arsenic and phosphorus, both highly toxic to humans, and the use of this chemical for ripening is illegal in most countries.
Ethylene has been found not harmful or toxic to humans in the concentrations found in ripening rooms.
In fact, ethylene was used medically as a anesthetic in concentrations significantly greater than that found in a ripening room. However, ethylene is often targeted as the reason for difficulty in breathing in ripening rooms; what can affect some people is usually either:
Carbon Dioxide (CO2,) levels: CO2, is produced by the ripening fruit in the room and levels increase over time, or
Oxygen levels: The oxygen in the room when loaded is taken in by the ripening fruit. This sometimes will make breathing in a ripening room difficult. The increased CO2, and decreased oxygen levels are the main reasons for venting the ripening room.
Ethylene action slows at lower temperatures.
At their minimum temperature levels, fruit is basically inactive and does not respond well to externally supplied ethylene.
Ethylene will penetrate most substances.
In fact, it will permeate through produce cardboard shipping boxes, wood and even concrete walls.
Ethylene is harmful to many fruits, vegetables, and floral items.
While ethylene is invaluable due to its ability to initiate the ripening process in several fruits, it can also be very harmful to many fruits, vegetables, flowers, and plants by accelerating the aging process and decreasing the product quality and shelf life. The degree of damage depends upon the concentration of ethylene, length of exposure time, and product temperature. One of the following methods should be used to ensure that ethylene-sensitive produce is not exposed:
Ethylene producing items (such as apples, avocados, bananas, melons, peaches, pears, and tomatoes) should be stored separately from ethylene-sensitive ones (broccoli, cabbage, cauliflower, leafy greens, lettuce, etc.). Also, ethylene is emitted by engines. Propane, diesel, and gasoline powered engines all produce ethylene in amounts large enough to cause damage to the ethylene-sensitive produce items mentioned;
Ventilate the storage area, preferably to the outside of the warehouse, on a continuous or regular basis to purge the air of any ethylene;
Remove ethylene with ethylene absorbing filters. These have been proven in reducing and maintaining low ethylene levels. If ethylene damage is suspected, a quick and easy way to detect ethylene levels is with hand held sensor tubes. This will indicate if the above steps should be followed.
Ethylene is explosive at high concentrations.
However, this occurs at 27,000 ppm; the amount used in ripening ranges from 5 - 150 ppm. When using catalytic generators as directed, it is not possible to create explosive levels of ethylene. There are several sources of ethylene application systems available; the safest form is ethylene generators and concentrate. In fact, the United Kingdom's HSE has stated in a document that "the use of cylinders of pure ethylene should be vigorously discouraged."
Ethylene is used to 'degreen' citrus.
This is a natural process that triggers pigment changes: the loss of green peel color by removing the chlorophyll, which allows the orange or yellow to fully cover the entire peel. No loss of flavor is caused; this is merely a continuation of the natural plant process. Extremely low leves of 1-10 ppm are required.
Does Ethrel or Ethephon work in ripening bananas and other fruits?
Ethephon is a plant growth regulator used to promote fruit ripening, abscission, flower induction, and other responses by releasing ethylene gas. Ethephon is registered for use by the US-EPA on a number of food, feed and nonfood crops, greenhouse nursery stock, and outdoor residential ornamental plants, but is used primarily on cotton. Formulations include formulation intermediates and soluble concentrates/liquids. Ethephon is applied to plant foliage by either ground or aerial equipment. It is not registered for use on bananas nor is it designed for post-harvest use. For commercial fruit ripening, the most effective and efficient ethylene application method is an ethylene generator.
How effective is "Banana Gas 32™", BANARG™ and other ethylene gas mixtures?
Since ethylene is explosive, these products contain an inert, non-flammable gas so that when released into an enclosed space like a ripening room, no explosive level of ethylene can be reached. The inert used is either Carbon Dioxide or Nitrogen. These mixtures will ripen fruit, but it does require large doses to reach 100 ppm of ethylene. Also, when applying ethylene in this manner, the fruit is also being exposed to large amounts of carbon dioxide or nitrogen; these are ripening inhibitors and will counteract the ethylene by causing the fruit to decrease respiration...or "sleep" and not receive the ethylene action. Better results are typically achieved using pure ethylene from generators or cylinders!
What is the best way to measure ethylene ppm levels?
There are several methods, and each has their advantage. What is best for one may not be for another, so the user would have to decide what is "best."
Air Sampling System / Tubes. These pass a measured amount of air from the area sampled through a filament that reacts with ethylene. After a few minutes, the filament changes color and the approximate ethylene level can be read on the tube. Accuracy is 25%. By far the most popular way to measure ethylene.
Digital Ethylene Detectors. Almost instant readings. Accuracy is approximately 2%, but unit must be in calibration!
Gas Chromatograph. By far the most accurate, into the part per billion (ppb) level, this method is also very time consuming and normally not performed on site.
*Some information taken from: California Fresh Market Advisory Board, Informational Bulletin No. 12, June 1, 1976.
"Banana Gas 32™" is a trademark of Praxair Tecnology Inc.; BANARG™is a trademark of Linde Gas.