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About Ethylene GasEthylene Gas C2H4 Ethylene gas (C2H4) is an odorless, colorless gas that exists in nature and is also created by man-made sources. Not easily detectable, it exists where produce is stored. In nature, the largest producers are plant and plant products (ie. fruits, vegetables and floral products) which produce ethylene within their tissues and release it into the surrounding atmosphere. It is also a by-product of man-made processes, such as combustion. As is often the case, the role of ethylene and its effects on produce was discovered by accident. Lemon growers would store newly harvested green lemons in sheds kept warm by kerosene heaters until they turned yellow and ripened enough to market. When new modern heating systems were tried, the lemons no longer turned yellow on time. Research soon found that the important factor in the ripening process was small amounts of ethylene gas given off by the burning kerosene in the heaters. Ethylene, also known as the 'death' or 'ripening hormone' plays a regulatory role in many processes of plant growth, development and eventually death. Fruits, vegetables and flowers contain receptors which serve as bonding sites to absorb free atmospheric ethylene molecules. The common practice of placing a tomato, avocado or banana in a paper bag to hasten ripening is an example of the action of ethylene on produce. Increased levels of ethylene contained within the bag, released by the produce itself, serves as a stimulant after reabsorption to initiate the production of more ethylene. The overall effect is to hasten ripening, aging and eventually spoilage. A refrigerator acts in much the same way. Kept closed to retain the desired temperature, it also enables an increased concentration of ethylene to accumulate. Any closed environment, such as a truck trailer, shipping container or warehouse, will have a similar effect. Storage of produce items is of economic importance to the food and floral industry. Storage allows producers, handlers and sellers to spread availability over periods of strong and weak demand, maintaining supply and stabilizing cost. Ethylene Sensitivity Chart N=None H=High L=Low M=Medium VH=Very High VL=Very Low Perishable Temperature Ethylene Ethylene Commodities C / F Production Sensitivity Fruits & Vegetables Apple (non-chilled) 1.1 / 30 VH H Apple (chilled) 4.4 / 40 VH H Apricot -0.5 / 31 H H Artichoke 0 / 32 VL L Asian Pear 1.1 / 34 H H Asparagus 2.2 / 36 VL M (Toughness) Avocado (California) 3.3 / 38 H H Avocado (Tropical) 10.0 / 50 H H Banana 14.4 / 58 M H Beans (Lima) 0 / 32 L M Beans (Snap/Green) 7.2 / 45 L M Belgian Endive 2.2 / 36 VL M Berries (Blackberry) -0.5 / 31 L L (Mold) Berries (Blueberry) -0.5 / 31 L L (Mold) Berries (Cranberry) 2.2 / 36 L L (Mold) Berries (Currants) -0.5 / 31 L L (Mold) Berries (Dewberry) -0.5 / 31 L L (Mold) Berries (Elderberry) -0.5 / 31 L L (Mold) Berries (Gooseberry) -0.5 / 31 L L (Mold) Berries (Loganberry) -0.5 / 31 L L (Mold) Berries (Raspberry) -0.5 / 31 L L (Mold) Berries (Strawberry) -0.5 / 31 L L (Mold) Breadfruit 13.3 / 56 M M Broccoli 0 / 32 VL H (Yellowing) Brussel Sprouts 0 / 32 VL H Cabbage 0 / 32 VL H Cantalope 4.4 / 40 H M Cape Gooseberry 12.2 / 54 L L Carrots (Topped) 0 / 32 VL L (Bitterness) Casaba Melon 10.0 / 50 L L Cauliflower 0 / 32 VL H Celery 0 / 32 VL M Chard 0 / 32 VL H Cherimoya 12.8 / 55 VH H Cherry (Sour) -0.5 / 31 VL L (Softening) Cherry (Sweet) -1.1 / 30 VL L (Softening) Chicory 0 / 32 VL H Chinese Gooseberry 0 / 32 L H Collards 0 / 32 VL M Crenshaw Melon 10.0 / 50 M H Cucumbers 10.0 / 50 L H (Yellowing) Eggplant 10.0 / 50 L L Endive (Escarole) 0 / 32 VL M Feijoa 5.0 / 41 M L Figs 0 / 32 M L Garlic 0 / 32 VL L (Odor) Ginger 13.3 / 56 VL L Grapefruit (AZ,CA,FL,TX) 13.3 / 56 VL M (Mold) Grapes -1.1 / 30 VL L (Mold) Greens (Leafy) 0 / 32 VL H (Russet Spotting) Guava 10 / 50 L M Honeydew 10 / 50 M H Horseradish 0 / 32 VL L Jack Fruit 13.3 / 56 M M Kale 0 / 32 VL M Kiwi Fruit 0 / 32 L H Kohlrabi 0 / 32 VL L Leeks 0 / 32 VL M Lemons 12.2 / 54 VL M (Mold) Lettuce (Butterhead) 0 / 32 L M (Russet Spotting) Lettuce (Head/Iceberg) 0 / 32 VL H (Russet Spotting) Lime 12.2 / 54 VL M (Mold Degreen) Lychee 1.7 /35 M M Mandarine 7.2 / 45 VL M Mango 13.3 / 56 M H Mangosteen 13.3 / 56 M H Mineola 3.3 / 38 L L Mushrooms 0 / 32 L M Nectarine -0.5 / 31 H H Okra 10.0 / 50 L M Olive 7.2 / 45 L M Onions (Dry) 0 / 32 VL L (Odor) Onions (Green) 0 / 32 VL M Orange (CA,AZ) 7.2 / 45 VL M Orange (FL,TX) 2.2 / 36 VL M Papaya 12.2 / 54 H H Paprika 10.0 / 50 L L Parsnip 0 / 32 VL L Parsley 0 / 32 VL H Passion Fruit 12.2 / 54 VH H Peach -0.5 / 31 H H Pear (Anjou,Bartlett/Bosc) 1.1 / 30 H H Pear (Prickley) 5.0 / 41 N L Peas 0 / 32 VL M Pepper (Bell) 10.0 / 50 L L Pepper (Chile) 10.0 / 50 L L Persian Melon 10.0 / 50 M H Persimmon (Fuyu) 10.0 / 50 L H Persimmon (Hachiya) 0.5 / 41 L H Pineapple 10.0 / 50 L L Pineapple (Guava) 5.0 / 41 M L Plantain 14.4 / 58 L H Plum/Prune -0.5 / 31 M H Pomegranate 5.0 / 41 L L Potato (Processing) 10.0 / 50 VL M (Sprouting) Potato (Seed) 4.4 / 40 VL M Potato (Table) 7.2 / 45 VL M Pumpkin 12.2 / 54 L L Quince -0.5 / 31 L H Radishes 0 / 32 VL L Red Beet 2.8 / 37 VL L Rambutan 12.2 / 54 H H Rhubard 0 / 32 VL L Rutabaga 0 / 32 VL L Sapota 12.2 / 54 VH H Spinach 0 / 32 VL H Squash (Hard Skin) 12.2 / 54 L L Squash (Soft Skin) 10.0 / 50 L M Squash (Summer) 7.2 / 45 L M Squash (Zucchini) 7.2 / 45 N N Star Fruit 8.9 / 48 L L Swede (Rhutabaga) 0 / 32 VL L Sweet Corn 0 / 32 VL L Sweet Potato 13.3 / 56 VL L Tamarillo 0 / 32 L M Tangerine 7.2 / 45 VL M Taro Root 7.2 / 45 N N Tomato (Mature/Green) 13.3 / 56 VL H Tomato (Brkr/Lt Pink) 10.0 / 50 M H Tree-Tomato 3.9 / 39 H M Turnip (Roots) 0 / 32 VL L Turnip (Greens) 0 / 32 VL H Watercress 0 / 32 VL H Watermelon 10,0 / 50 L H Yam 13.3 / 56 VL L Live Plants Cut Flowers (Carnations) 0 / 32 VL H (Sleepiness) Cut Flowers (Chrysanthemums) 0 / 32 VL H Cut Flowers (Gladioli) 2.2 / 36 VL H Cut Flowers (Roses) 0 / 32 VL H (Open Sooner) Potted Plants -2.8-18.3 / 27-65 VL H Nursery Stock -1.1-4.4 / 30-40 VL H (Slower Start) Christmas Trees 0 / 32 N N Flowers Bulbs (Bulbs/ 7.2-15 / 45-59 VL H Corms/Rhizomes/Tubers) 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 Discovery1901 Neljubow in St. Petersburg Russia:
1910 Oranges cause bananas to ripen prematurely (natural ethylene?) 1934 Ethylene is a natural product (plant hormone?) Forgotten for many years as possible hormone.... 1959 Burg & Thimann rediscover old research and begin studies showing ethylene as possible hormone EFFECTSFruit 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: 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. Ethylene CAS No. 74-85-1Synonym. Acetene; Elayl; Ethene. Properties. Colorless gas with a faint odor of ether. Solubility in water is 20 mg/1 (20°C) and 250 mg/l (0°C). Rapidly volatilizes from the open surface of water. Odor perception threshold is reported to be 0.039 mg/l,02 = 0.5 mg/l,010 or even 260 mg/l.010 Does not affect the color or clarity of water. Acute Toxicity. Mice tolerate administration of 0.5 ml of a solution with a concentration of 150 mg E./l without changes in their behavior. Repeated Exposure. Accumulation is impossible because of the rapid excretion of E. from the body. Short-term Toxicity. Mice were dosed by gavage with 3.75 mg/kg BW for 4 month. The treated animals displayed no changes in behavior or in BW gain and oxygen consumption. Gross pathological examination revealed no changes in the relative weights or in the histological structure of the visceral organs.1 Long-term Toxicity. Rats were given 0.05 mg/kg BW for 6 month. The treatment produced little abnormalities in behavior, BW gain, leukocyte phagocytic activity, or in cholinesterase anal conditioned reflex activity.' Genotoxicity and Carcinogenicity. Experiments proved E. to be converted in certain species notably mice and rats, into the carcinogenic and mutagenic ethylene oxide.2 Carcinogenic effect of E. of endogenous origin is suggested.3 Whether such an effect is possible with oral administration is not clear. No toxic or carcinogenic effects were found after inhalation of 300 to 3000 ppm.4 Carcinogenicity Classification. IARC: Group 3. Chemobiokinetics. It is unlikely that there is a direct chemical interaction between E. and bio logical media. 1:. is not broken down in the body. It seems to he rapidly excreted via the lungs Standards. Russia (1988) MAU and PML: 0.5 mg/l (organolept., odor). References:
source: Sheftel, VO. Handbook of Toxic Properties of Monomers and Additives. 1995 |
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