The Garden's Cure - View Single Post

**Lou Cypher** · 07-23-2008, 12:59 PM

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Ethylene is a plant hormone that differs from other plant hormones in being a gas. When fruits approach maturity, they release ethylene. Ethylene promotes the ripening of fruit. Among the many changes that ethylene causes is the destruction of chlorophyll. With the breakdown of chlorophyll, the red and/or yellow pigments in the cells of the fruit are unmasked and the fruit assumes its ripened color.

How the role of ethylene was discovered.

As is so often the case in science, the discovery of the role of ethylene was made by accident. When first harvested, lemons are often too green to be acceptable in the market. In order to hasten the development of a uniform yellow color, lemon growers used to store newly-harvested lemons in sheds kept warm with kerosene stoves. When one grower tried a more modern heating system, he found that his lemons no longer turned yellow on time. Following this clue, it was soon found that

EFFECTS
Fruit Ripening

Abscission; leaf flower fruits (thinning, harvesting)

Epinasty

Triple Resonses

Hook Closure Maintenance

Initiates Germination in Grains

Activates dormant buds (potatoes in storage)

Stem elongation in deep-water rice

Induces Flowering in Pineapple

Promotes Female Expression in Flowers

Flower and Leaf Senescence: Ag preventative (vase life)

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:
a) Carbon Dioxide (CO2,) levels: CO2, is produced by the ripening fruit in the room and levels increase over time, or
b) 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.

It will permeate through produce cardboard shipping boxes, wood and even concrete walls.

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: a) 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; b) Ventilate the storage area, preferably to the outside of the warehouse, on a continuous or regular basis to purge the air of any ethylene; c) 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. When using as directed, reaching the explosive level is not possible. The explosive level is about 200 times greater than that found in ripening rooms.

Ethylene was used historically as an important anesthetic until less flammable compounds were developed. It is a colorless gas with a sweet ether-like odor. As an anesthetic, it was used as a concentration of 85% with 15% oxygen. Ethylene is a hydrocarbon gas and quite flammable and explosive at concentrations above about 3%. Remember, a non-toxic anesthetic for humans at a concentration of 85% or higher, yet as a fruit ripening hormone, ethylene gas is effective at 0.1 to 1 ppm. One part of ethylene per million parts of air that's one cupful of ethylene gas in 62,000 gallons of air - is enough to promote the ripening process in fruits.

Using tomatoes as an example, the life of a tomato fruit begins with fertilization of the flower ovules. After fertilization, the young fruit goes through a short period of cell division which is then followed by a rapid period of growth as these cells enlarge. During the final stages of growth and development, the tomato fruit reaches its full size and is now mature. This period of growth and development, from fertilization to development of the mature fruit, requires about 45-55 days, depending on the cultivar and the season. During the growth and development period, there are many chemical and physical changes occurring that have an impact on fruit quality and ripening behavior after harvest. Ripening is the final stage of the maturation process when the fruit changes color, and develops the flavor, texture and aroma that makes up what we define as optimum eating quality. The biological agent that initiates this ripening process after the fruit is mature is naturally produced ethylene - this simple plant hormone described and understood over 40years ago. While there are other factors involved in this "triggering" of the ripening process by ethylene, it is essentially a universal ripening hormone. When this internal concentration of naturally produced ethylene increases to about 0.1 - 1.0 ppm, the ripening process is irreversibly initiated. The process may be slowed, but it cannot be reversed once it is truly under way. So, here is the key point: additional and externally applied ethylene, provided prior to the time that the naturally produced internal concentration reaches the required 0.1 - 1.0 ppm level, will trigger or initiate - "promote" if you will - this natural ripening process at an earlier time.

The additional externally applied ethylene (the "gassing" so frequently referred to in the popular press) 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.

For example, tomato fruit are not and cannot be "artificially reddened" by ethylene. The normal tomato ripening process, which includes pigment changes - the loss of green chlorophyll and conversion of carotenoids into red lycopene pigments - can be accelerated and brought about earlier by externally applied ethylene, but this is a normal process. In fact, some of the components of nutritional quality, such as Vitamin C content, benefit because of the fact that the fruits will be consumed after a shorter time interval from harvest as a result of ethylene treatments and hence, the initial level will not have degraded as far as the longer, unaccelcratcd process. Ethylene is actually used commercially on only a few crops, including: (a) bananas, (b) for removing the green color from citrus fruits, (e) almost all honeydew melons, and (d) to a limited extent, with tomatoes.

Although many factors could be listed, there are four which play the dominant role in determining the quality of tomato fruits presented to the customer in the retail store: (1) variety; (2) maturity at time of harvest; (3) storage temperature during shipping and handling, and (4) physical damage.

Source: California Fresh Market Advisory Board, Informational Bulletin No. 12, June 1, 1976.